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Looking for a Psa-related project or report? Select from the headings below to view all research material applicable to that subject matter.
None of the tank mixes showed reduced efficacy of the pest or disease control targeted. Prodigy (Brown Headed Leaf Roller), Luna Privilege (sclerotinia), Kocide Opti (Psa) and Actigard (Psa) were found to be compatible, as tank mixing of these products did not affect the efficacy of Prodigy against neonate Brown Headed Leaf Roller larvae or Luna Privilege against Sclerotinia.
The trial was established to determine the effects of an intensive autumn spray protection programme on Gold3 and Hort16A. It was difficult to separate treatment effects as the Gold3 site had little infection and the Hort16A site had too much infection. There was a trend for treatment programmes including a full programme with coppers, foliar applied elicitors and KeyStrepto™ to reduce the effects of Psa-V by comparison with other lesser treatment programmes.
This trial assessed the performance of a range of products on Hayward under very high infection pressure. The untreated control resulted in between 47% and 53% severity of spotting, and only achieved a mere 45% fruitset from available flowers due to Psa bud rot.
This was to created to test the efficacy of potential Psa control products, using Hort16A potted plants inoculated with Psa. Products were applied pre or post Psa inoculation, as recommended, and disease symptoms assessed over a four week period, including leaf spotting and secondary symptoms.
This final report is a summary of key activities and outcomes over the past 15 months on a project designed towards testing on a commercial scale, a comprehensive spray programme, developed from results of previous trials, to minimise the impacts of Psa-V on orchard productivity.
Zespri engaged HortEvaluation Ltd to evaluate products with demonstrated efficacy against Psa leaf spot over the leaf fall period. The trial was established at two sites with Gold3 and Hayward vines in the Bay of Plenty, within Psa recovery zones.
Psa product testing by Zespri/KVH started soon after Psa was first discovered. Initial testing was relatively ad hoc in an early attempt to find a quick win solution.
Treatments to limit the spread of Psa in orchards are required. Requested preliminary in vitro testing of products for activity against Psa.
With the arrival of Psa we have seen the rapid infection of male vines used in conjunction with all the commercial kiwifruit varieties. This leaves the industry with the possibility of being unable to ensure adequate pollination for the crop. In the case of Hort16A this shortfall was supplemented by artificial pollination using Chieftain pollen however Hayward males are also becoming infected more rapidly than females and we are left in the position of having inadequate pollen available on badly affected orchards. This, combined with finding Psa-V on pollen, has led to a demand to disinfect pollen from Psa-V contamination. Heat disinfection did not work for high Psa-V concentrations so this project was initiated to examine the possible use of ozone.
The key purpose of this project was to determine whether Psa-V could survive throughout the different stages of the commercial pollen milling process and remain viable in green kiwifruit pollen. While it was known that Psa-V would be present on flowers from infected orchards, there was less certainty around recovery of Psa-V from flowers collected from orchards with little or no disease. It was also unknown whether viable Psa-V colonies could be recovered from pollen after commercial milling and extraction, thus potentially providing a source of infection for the disease.
A study in 2011 demonstrated the ability of Psa to survive for several days in a beehive, but it was not known how much, if any, Psa-V (the virulent form of the disease) would be carried by honey bees foraging in an infected kiwifruit orchard. The aim of this project was to determine this, and secondarily to assess for how long Psa-V could be detected in these colonies once the hives were removed from a source of inoculum. The purpose of this research is to provide Zespri, growers and beekeepers with the information they need to determine what risk the introduction of beehives into their orchard has in relation to Psa-V contamination of their vines.
The aims were to repeat previous observations that honey bees redistribute dry pollen blown onto pistillate kiwifruit flowers and the effect of the amount of dry pollen applied on pollen redistribution; investigate the direct effect of increasing the rate of pollen blown on to flowers; and investigate the effectiveness of pollen dispensers used to dust honey bees with kiwifruit pollen as they leave their hives.
During this project 694 leaf and 676 pollen (extracted from closed male flowers) samples
from symptomatic and asymptomatic vines of Zespri Gold kiwifruit were collected and tested for the presence of Psa. Symptomatic vines were those male kiwifruit vines showing primary and/or secondary symptoms, or were adjacent to infected kiwifruit vines. Asymptomatic vines were vines with no visual evidence of disease on the vine or in the orchard block.
The key purpose of this project is to ensure growers have access to pollen with a known minimal risk of contamination of live Psa.
A series of physical and chemical treatments were tested for, firstly, removal of all contaminating bacteria from pollen, then for removing Psa from pollen that was artificially cleaned and then recontaminated with Psa.
We have found that at least one sample of pollen collected from Italy in an infected orchard contained some live cells of Psa. Presence of Psa on pollen has some important economic consequences knowing that most kiwifruit orchards are artificially pollinated and that Psa is a potential epiphytic bacterium. Results from Italy might not be extrapolated to New Zealand because of the differences in kiwifruit pollen collection methods used in Italy (vacuumed from open flowers in the field) and in New Zealand (pollen milled from flowers collected as closed flowers in the field). Therefore, the aim of this study was to determine whether Psa was associated with kiwifruit pollen collected in New Zealand, or with kiwifruit pollen collected overseas and present in New Zealand.
This project looked for differences in microbiome diversity between vines affected by Pseudomonas syringae pv.actinidiae (Psa) and those not affected, and between commercial and wild kiwifruit vines living in similar environments. This information could lead to the development of novel ways of reducing the incidence of Psa.
Work commissioned by Zespri and KVH to better understand the microbiome on New Zealand kiwifruit has provided the industry with reports and culture collections which may in the future help identify potential biological control agents for the industry.
This three year study by Plant and Food Research included review of historical (pre-Psa incursion) samples, and samples collected from across New Zealand in 2017 and 2018.
High-level outcomes have been made available from this study.
The efficacy of Emix against Psa is dose dependent, with results in this study showing that higher concentrations of Emix are required to control Psa in more complex environments. The combination of Aureo Gold (0.5g/L) + Emix (1 g/L) was more effective against Psa than the individual components alone.
This trial with Aureo Gold investigated the impact the applications have on components of yield and fruit quality. The results showed that Aureo Gold did not have negative impacts on components of yield or fruit quality parameters at harvest/post-harvest.
No significant differences in the sepal browning, fruitset, fruit weight and fruit shape were observed between the untreated control and any of the applied treatments in this study. None of the treatments had a negative impact on the pollination, or yield components of Hayward kiwifruit.
Zespri/KVH are seeking alternative products to control Psa in kiwifruit that can complement or substitute for the kiwifruit sector’s current reliance upon copper-based products, antibiotics and Actigard® for the control of Psa.
Zespri, with support from KVH, is coordinating the screening of the effectiveness of a wide range of products to control Psa-V. The screening programme has been developed to identify options for managing Psa-V.
To test the efficacy of various yeast mix (provided by Plant & Food Research) and trichoderma (provided by the Bioprotection Research Centre) treatments.
To test the efficacy of foliar applied treatments at protecting kiwifruit plants from Psa-V. Specifically, the following were studied: Biological Control Agents (BCAs) on G14; elicitors and Protectants on G9; elicitors on Chieftain.
Psa product testing by Zespri/KVH started soon after Psa was first discovered. Initial testing was relatively ad hoc in an early attempt to find a quick win solution.
The following report presents the findings of a desktop evaluation of biocontrol agents
with potential to control or suppress bacterial canker of kiwifruit caused by Psa. The review identifies the most likely candidates of locally available and overseas products based on a ranking approach and discusses their suitability.
Environmental samples of soil and leaf litter have been used for the isolation of bacteriophages that infect Psa. To date 51 bacteriophages have been isolated and lysate of each bacteriophage prepared and titrated. Based on the plaque morphology greater than 5 clearly distinct bacteriophages have been isolated. A more through characterisation of the bacteriophage isolates is likely to increase this number. Preliminary host-range analysis suggests that the phages may be useful as a typing/diagnostic toolkit.
Treatments to limit the spread of Psa in orchards are required. Requested preliminary in vitro testing of products for activity against Psa.
Our bacteriophage collection now contains roughly 100 bacteriophage. Redundancy (multiple isolations of the same phage) in the collection remains likely and furthermore we do not know which bacteriophage are likely to be the most effective as biocontrol agents. To establish the level of redundancy we are performing host range analysis, which will allow us to group the phage. Given that the bacterial hosts we are testing include potential beneficial microbes and biocontrol agents, this will also allow us to identify any phage that can infect and be amplified on carrier bacteria.
Tank mixing of Kocide Opti with Proclaim did not affect Psa control. Emamectin residues were increased in the Kocide Opti + Proclaim mix, suggesting a positive chemical interaction which increased the longevity of the emamectin residue. Copper and emamectin residues were reduced 2-4 fold with the addition of Duwett®, but this was a physical effect of spray application via a hand sprayer.
None of the tank mixes showed reduced efficacy of the pest or disease control targeted. Prodigy (Brown Headed Leaf Roller), Luna Privilege (sclerotinia), Kocide Opti (Psa) and Actigard (Psa) were found to be compatible, as tank mixing of these products did not affect the efficacy of Prodigy against neonate Brown Headed Leaf Roller larvae or Luna Privilege against Sclerotinia.
Inocbloc and copper paste confirmed to show efficacy for protecting wounds. However, neither product should be used on grafts (death of potted plants) or girdles. Abnormal swelling above the girdle was observed.
Horizontal gene transfer can precipitate rapid evolutionary change. In 2010 the global pandemic of kiwifruit canker disease caused by Psa reached New Zealand. At the time of introduction, the single clone responsible for the outbreak was sensitive to copper, however, analysis of a sample of isolates taken in 2015 and 2016 showed that a quarter were copper resistant.
Genome sequences of seven strains showed that copper resistance along with resistance to arsenic and cadmium, was acquired via uptake of integrative conjugative elements (ICEs), but also plasmids.
A number of products were tested. Citrox BioAlexin™ consistently increased the concentration of Cu2+ on plant leaf surfaces when applied after copper. Consistent reductions in Cu2+ release were observed when Acadian was applied prior to, as a tank mix, or post Nordox® and Kocide® applications.
Inocbloc and copper paste consistently protected pruning wounds on kiwifruit vines from infection by Psa-V, in both potted plant trials and in the field.
No significant differences in the sepal browning, fruitset, fruit weight and fruit shape were observed between the untreated control and any of the applied treatments in this study. None of the treatments had a negative impact on the pollination, or yield components of Hayward kiwifruit.
The trial was established to determine the effects of an intensive autumn spray protection programme on Gold3 and Hort16A. It was difficult to separate treatment effects as the Gold3 site had little infection and the Hort16A site had too much infection. There was a trend for treatment programmes including a full programme with coppers, foliar applied elicitors and KeyStrepto™ to reduce the effects of Psa-V by comparison with other lesser treatment programmes.
Optimising copper use for sustainable control of Psa in kiwifuit orchards. This study was undertaken to build on previous work to develop best practice recommendations for protective sprays for kiwifruit. In particular, it was to determine (1) for how long low-drift air inclusion (AI) nozzles could efficiently deliver protectant sprays to expanding spring canopies, and (2) to maximise the efficiency of spray delivery to flowering Hayward and fully expanded Gold3 canopies on wide row spacings.
HortEvaluation Ltd were engaged by Zespri to undertake a study to determine whether copper applied with a superspreader or a penetrant adjuvant at late leaf fall causes phytotoxicity to buds. A second objective of this project was to evaluate efficacy for Psa disease control.
This trial assessed the performance of a range of products on Hayward under very high infection pressure. The untreated control resulted in between 47% and 53% severity of spotting, and only achieved a mere 45% fruitset from available flowers due to Psa bud rot.
This was to created to test the efficacy of potential Psa control products, using Hort16A potted plants inoculated with Psa. Products were applied pre or post Psa inoculation, as recommended, and disease symptoms assessed over a four week period, including leaf spotting and secondary symptoms.
Copper spraying has become a significant component of the kiwifruit industries spray programme for providing protection against infection by Psa-V. The industry has made significant progress in its understanding of copper use over the 3 years since Psa-V was identified in New Zealand, through field trials and grower experience. However, there are still many questions around the optimising of efficacy and avoiding phytotoxicity that warrant developing a better understanding of how copper works once applied to plants.
This final report is a summary of key activities and outcomes over the past 15 months on a project designed towards testing on a commercial scale, a comprehensive spray programme, developed from results of previous trials, to minimise the impacts of Psa-V on orchard productivity.
This trial was established to determine the efficacy of three, previously untested copper products, (copper hydroxide, copper oxide and chelated copper), in reducing Psa infection in Bruno kiwifruit plants. Two products were tested at different concentrations to determine the most effective rate and one product, the chelated copper, was applied four times. Nordox was used as the positive control.
During the summer of 2012/13 two trials were established in a Gold 3 orchard located in Gisborne in the North Island of New Zealand. Trial objectives were to determine if there is a period post flowering when copper use should be avoided due to damage to fruit, which leads to an increase in fruit rejects; and to determine if rates of copper, addition of adjuvants or repeat applications of copper increase the risk of damage to fruit.
To test the efficacy of foliar applied treatments at protecting kiwifruit plants from Psa-V. Specifically, the following were studied: Biological Control Agents (BCAs) on G14; elicitors and Protectants on G9; elicitors on Chieftain.
Psa product testing by Zespri/KVH started soon after Psa was first discovered. Initial testing was relatively ad hoc in an early attempt to find a quick win solution.
A woody stem bioassay that enables the assessment of a cultivar’s tolerance to Psa has been developed by Plant & Food Research. The objective of this study was to determine the susceptibility of vines from two Hort16A orchards to Psa-V. The Roan Orchard received copper a application seven weeks prior to cane sampling and the Nola Orchard received a copper application nine weeks prior to cane sampling.
A preliminary trial was conducted in Opotiki during summer 2011-12 to determine whether Gold3 has a window of high sensitivity to copper damage. Nordox 750WG, a formulation of cuprous hydroxide, and Latron B-1956, a surfactant, were applied to vines.
Seventeen different copper treatments were applied to both Hayward and Hort16A canopies, from bud break to fruit set, to evaluate the effect of the treatments on leaf and fruit health, by comparison with an untreated control.
Two studies were undertaken to determine (1) how rainfall affects residues of commercial
copper sprays on Hort 16A and Hayward dormant canes (both old and replacement wood) and (2) how rainfall affects residues of organic copper + oil sprays on Hayward replacement canes.
Treatments to limit the spread of Psa in orchards are required. Requested preliminary in vitro testing of products for activity against Psa.
None of the tank mixes showed reduced efficacy of the pest or disease control targeted. Prodigy (Brown Headed Leaf Roller), Luna Privilege (sclerotinia), Kocide Opti (Psa) and Actigard (Psa) were found to be compatible, as tank mixing of these products did not affect the efficacy of Prodigy against neonate Brown Headed Leaf Roller larvae or Luna Privilege against Sclerotinia.
Mid, and early plus mid, treatments with Ambitious resulted in a significant reduction in Psa leaf spot on Hayward. In this trial, Ambitious was the only Psa disease control product applied between bud-break and flowering. There were no differences in % reject fruit versus untreated control.
Trials testing the efficacy of Ambitious for controlling Psa on mature Hayward vines showed Ambitious was effective in reducing the severity of leaf spotting and performed similar to Actigard. Ambitious did not appear to show any efficacy on reducing the levels of bud rot and bud loss.
Trials at two high inoculum sites in the Bay of Plenty showed application of Ambitious mid-season (between budbreak and flowering) significantly reduced Psa leaf spot on mature Hayward kiwifruit vines. No significant differences in percentage flowers retained, fruit set or reject fruit type was observed between trial and control plots.
Application of post-harvest Actigard® induced an upregulation of “defence marker“ genes in both Zesy002 (Gold3) and Hayward vines.
Gene expression patterns varied over time and differed between sites and cultivars. These patterns were consistent with Actigard® operating by upregulation of the salicylic acid defence pathway. This supports the value of applying Actigard® or copper plus Actigard® in the post-harvest window to help vines fight Psa infection.
Leaf health and integrity determined the level of vine response rather than the date of Actigard® application.
There was no evidence that the effects of post-harvest Actigard® application are carried over into the following spring.
Responsiveness of Actinidia chinensis var.deliciosa Hayward and Actinidia chinensis var.chinensis Zesy002 (Gold3) vines to post-harvest Actigard was investigated by comparing gene expression of eight defence marker genes following application to early and late harvest orchards.
Results showed early-harvest and late-harvest Hayward vines both responded to Actigard, with patterns of defence gene up-regulation similar.
Gold3 samples were lost through equipment (freezer) failure so this data is not available.
Evidence for a carry-over response into the following spring was not conclusive.
The efficacy of Emix against Psa is dose dependent, with results in this study showing that higher concentrations of Emix are required to control Psa in more complex environments. The combination of Aureo Gold (0.5g/L) + Emix (1 g/L) was more effective against Psa than the individual components alone.
This trial was established to investigate the field efficacy of a number of promising elicitors, as identified in potted plant trials, to control Psa.
However, the trial was not able to demonstrate efficacy of any of the products tested, including the positive control Actigard, in providing additional control of Psa disease symptoms, on both Hayward and Gold3 mature vines.
Actigard was observed to have an impact on floralness in Gold3 (reduced), however it also had an impact on improving dry matter, fresh weight and other maturity parameters.
None of the tank mixes showed reduced efficacy of the pest or disease control targeted. Prodigy (Brown Headed Leaf Roller), Luna Privilege (sclerotinia), Kocide Opti (Psa) and Actigard (Psa) were found to be compatible, as tank mixing of these products did not affect the efficacy of Prodigy against neonate Brown Headed Leaf Roller larvae or Luna Privilege against Sclerotinia.
Mid, and early plus mid, treatments with Ambitious resulted in a significant reduction in Psa leaf spot on Hayward. In this trial, Ambitious was the only Psa disease control product applied between bud-break and flowering. There were no differences in % reject fruit versus untreated control.
Increased concentrations of procyanidin polyphenol metabolites were found in leaves from root pruned vines taken 2 days after root pruning but not at subsequent sampling times. This response was associated with root pruning. We found no evidence for an effect of Actigard™ on the procyanidin metabolism in leaves. The procyanidin response to root pruning is similar to that observed by us in previous trunk girdling experiments with Hort16A Actinidia chinensis var. chinensis Hort16A and A. chinensis var. deliciosa Hayward vines, and by others studying metabolic responses of plants to stress. This work has helped elucidate a key metabolic response to wounding in kiwifruit that may be implicated in disease response. Further work is underway.
The novel elicitor Estim, showed promise in controlling Psa in Bruno potted plant trials. Efficacy on Gold varieties also cannot be discounted.
No significant differences in the sepal browning, fruitset, fruit weight and fruit shape were observed between the untreated control and any of the applied treatments in this study. None of the treatments had a negative impact on the pollination, or yield components of Hayward kiwifruit.
Field trials on potted Gold3 plants tested efficacy of a range of elicitors in inducing a plant immune response to Psa. TNL3454 (at higher concentrations) and AB48414 showed a level of Psa control comparable to Actigard™ for up to six weeks post-Psa inoculation. Citrox BioAlexin showed some significant Psa control four weeks post inoculation. This product could offer organic growers an elicitor option. However, further trials to prove consistent efficacy would be advisable. ProAct and Silver combined and Luna Care did not show efficacy.
Trials testing the efficacy of Ambitious for controlling Psa on mature Hayward vines showed Ambitious was effective in reducing the severity of leaf spotting and performed similar to Actigard. Ambitious did not appear to show any efficacy on reducing the levels of bud rot and bud loss.
The trial was established to determine the effects of an intensive autumn spray protection programme on Gold3 and Hort16A. It was difficult to separate treatment effects as the Gold3 site had little infection and the Hort16A site had too much infection. There was a trend for treatment programmes including a full programme with coppers, foliar applied elicitors and KeyStrepto™ to reduce the effects of Psa-V by comparison with other lesser treatment programmes.
Trials at two high inoculum sites in the Bay of Plenty showed application of Ambitious mid-season (between budbreak and flowering) significantly reduced Psa leaf spot on mature Hayward kiwifruit vines. No significant differences in percentage flowers retained, fruit set or reject fruit type was observed between trial and control plots.
This trial assessed the performance of a range of products on Hayward under very high infection pressure. The untreated control resulted in between 47% and 53% severity of spotting, and only achieved a mere 45% fruitset from available flowers due to Psa bud rot.
This final report is a summary of key activities and outcomes over the past 15 months on a project designed towards testing on a commercial scale, a comprehensive spray programme, developed from results of previous trials, to minimise the impacts of Psa-V on orchard productivity.
To test the efficacy of foliar applied treatments at protecting kiwifruit plants from Psa-V. Specifically, the following were studied: Biological Control Agents (BCAs) on G14; elicitors and Protectants on G9; elicitors on Chieftain.
Zespri engaged HortEvaluation Ltd to evaluate products with demonstrated efficacy against Psa leaf spot over the leaf fall period. The trial was established at two sites with Gold3 and Hayward vines in the Bay of Plenty, within Psa recovery zones.
Psa product testing by Zespri/KVH started soon after Psa was first discovered. Initial testing was relatively ad hoc in an early attempt to find a quick win solution.
Tank mixing of Kocide Opti with Proclaim did not affect Psa control. Emamectin residues were increased in the Kocide Opti + Proclaim mix, suggesting a positive chemical interaction which increased the longevity of the emamectin residue. Copper and emamectin residues were reduced 2-4 fold with the addition of Duwett®, but this was a physical effect of spray application via a hand sprayer.
The efficacy of Emix against Psa is dose dependent, with results in this study showing that higher concentrations of Emix are required to control Psa in more complex environments. The combination of Aureo Gold (0.5g/L) + Emix (1 g/L) was more effective against Psa than the individual components alone.
None of the tank mixes showed reduced efficacy of the pest or disease control targeted. Prodigy (Brown Headed Leaf Roller), Luna Privilege (sclerotinia), Kocide Opti (Psa) and Actigard (Psa) were found to be compatible, as tank mixing of these products did not affect the efficacy of Prodigy against neonate Brown Headed Leaf Roller larvae or Luna Privilege against Sclerotinia.
The novel elicitor Estim, showed promise in controlling Psa in Bruno potted plant trials. Efficacy on Gold varieties also cannot be discounted.
Field trials on potted Gold3 plants tested efficacy of a range of elicitors in inducing a plant immune response to Psa. TNL3454 (at higher concentrations) and AB48414 showed a level of Psa control comparable to Actigard™ for up to six weeks post-Psa inoculation. Citrox BioAlexin showed some significant Psa control four weeks post inoculation. This product could offer organic growers an elicitor option. However, further trials to prove consistent efficacy would be advisable. ProAct and Silver combined and Luna Care did not show efficacy.
Field trials on potted Bruno plants further tested the efficacy of a range of potential Psa protectants. At the recommended concentration, Nanospada significantly decreased leaf spotting for up to three weeks post Psa inoculation. When diluted, Nanospada had no significant effect, supporting the use of the recommended rate. Another product, TNL3214, significantly reduced leaf spotting throughout the trial. KOF products only provided control when combined with Streptomycin.
This was to created to test the efficacy of potential Psa control products, using Hort16A potted plants inoculated with Psa. Products were applied pre or post Psa inoculation, as recommended, and disease symptoms assessed over a four week period, including leaf spotting and secondary symptoms.
Zespri, with support from KVH, is coordinating the screening of the effectiveness of a wide range of products to control Psa-V. The screening programme has been developed to identify options for managing Psa-V.
To test the efficacy of various yeast mix (provided by Plant & Food Research) and trichoderma (provided by the Bioprotection Research Centre) treatments.
Kiwifruit plants can often be infected with Psa but without symptoms. The time between infection and symptom development is known as the ‘latency’ phase. During that phase, infected plants are symptomless carriers.
It is extremely difficult to identify plants that are in a latency phase and to know how long the phenomenon can last. Understanding why an infected plant does not express symptoms and what are the triggers to break the latency phase (i.e. the triggers that will lead to the plant expressing symptoms) are important pieces of information that are needed to put in place strategies to prevent or manage outbreaks. A cover note summarising the report and results is available here.
Inocbloc and copper paste confirmed to show efficacy for protecting wounds. However, neither product should be used on grafts (death of potted plants) or girdles. Abnormal swelling above the girdle was observed.
Molecular analyses of microbial populations on diseased buds showed that Psa was the dominant species and that Psa was most likely the cause of bud rot. Girdling vines 30 days before flowering resulted in significantly less bud rot than in non-girdled vines. The effect was observed in both Hayward and Green14. The results suggest that girdling 30 days before bud break triggered a physiological response in the vine that limited the severity of bud rot.
Recurring epidemics of kiwifruit bleeding canker disease are caused by Psa. In order to strengthen understanding of population structure, phylogeography, and evolutionary dynamics, this project isolated Pseudomonas from cultivated and wild kiwifruit across six provinces in China.
Based on the analysis of 80 sequenced Psa genomes, we show that China is the origin of the pandemic lineage but that strain diversity in China is confined to just a single clade. Distinct independent transmission events marked introduction of the pandemic lineage into New Zealand.
The results of this work showed that Psa is present on both the outside of winter buds and within the buds themselves as they were expanding in the spring. The overall amount of Psa detected was low, however Psa was found more frequently from juvenile tissues from inside the buds (10.3%) than from the outside (5.1%). Consequently it appears that leaf spotting on the first expanding young leaves in the spring could be caused by either Psa from within the bud or Psa arriving on the expanding leaves.
A trial was undertaken by Kawerau-based Plateau Bark to see if compost could be made using reject fruit (and associated debris) mixed with pulp waste from the Norske Skog Tasman Ltd pulp and paper mill.
Optimising copper use for sustainable control of Psa in kiwifuit orchards. This study was undertaken to build on previous work to develop best practice recommendations for protective sprays for kiwifruit. In particular, it was to determine (1) for how long low-drift air inclusion (AI) nozzles could efficiently deliver protectant sprays to expanding spring canopies, and (2) to maximise the efficiency of spray delivery to flowering Hayward and fully expanded Gold3 canopies on wide row spacings.
Many kiwifruit vines in Psa infected orchards have leaves with Psa spots. In some Hayward orchards more than 50% of leaves have spots caused by Psa. If these lesions are producing Psa bacteria, these are potentially massive inoculum sources.
A study in 2011 demonstrated the ability of Psa to survive for several days in a beehive, but it was not known how much, if any, Psa-V (the virulent form of the disease) would be carried by honey bees foraging in an infected kiwifruit orchard. The aim of this project was to determine this, and secondarily to assess for how long Psa-V could be detected in these colonies once the hives were removed from a source of inoculum. The purpose of this research is to provide Zespri, growers and beekeepers with the information they need to determine what risk the introduction of beehives into their orchard has in relation to Psa-V contamination of their vines.
Previous work has shown that Psa survives in kiwifruit plant debris on the orchard floor at least until spring, but it is not known if this material poses a risk for re-infection of kiwifruit vines. This study used trap plates and trap plants to determine the importance of fallen leaves and winter prunings on the orchard floor as inoculum sources.
The influence of leaf age on infection by Psa was investigated using potted Hayward and Hort16A kiwifruit plants. Leaves were spray inoculated with an isolate of Psa (haplotype NZ-V) at a rate of 6.9 x 108 cfu/ml. Plants were maintained in a saturated environment in a plastic hot house within the confines of a containment laboratory at Plant & Food Research's Mt Albert Research Centre, Auckland.
Plant & Food Research has developed a preliminary predictive model (Beresford 2011) to identify weather conditions conducive to infection of kiwifruit plants with Psa that causes bacterial canker. The Psa Risk Model uses hourly wetness (or relative humidity), temperature and rainfall to calculate a daily risk index, R, which aims to identify days with weather conditions suitable for multiplication and infection of the Psa bacterium. The model is intended for use by NIWA to implement a web based information system to deliver the model to the kiwifruit industry.
Treatments to limit the spread of Psa in orchards are required. Etec have requested preliminary in vitro testing of three products for activity against Psa.
Twenty-one potential loci that might be able to distinguish the virulent isolate of Psa present in New Zealand (Psa-V) from other isolates of Psa present in New Zealand (Psa-LV), from other closely related pathovars of P. syringae and from other related pseudomonads were identified and tested by genome comparisons, in various PCR assays, and sequenced in order to identify a set of loci that best suited the characteristics required for developing a highly specific and rapid PCR-based assay for Psa-V.
The bacterial pathogen Psa was first detected in New Zealand kiwifruit vines in November 2010, and a virulent strain of this bacterium is causing serious vine losses. Knowledge of the biology and ecology of this pathogen is limited. In order to develop effective orchard management strategies to minimise disease incidence and spread, it is important to understand how the pathogen responds to the environment and its kiwifruit host, and gain a full understanding of the biology and life cycle in New Zealand orchards.
The current programme focused on where the Psa bacterium survives in the orchard,
particularly over the winter period. Various components of the kiwifruit orchard environment were investigated, including internal and external vine tissues, leaf litter and prunings, shelterbelts and weeds, soil and water.
Treatments to limit the spread of Psa in orchards are required. Etec have requested preliminary in vitro testing of three products for activity against Psa. This document reports on the growth rate testing of two of those products.
The bacterial plant disease Psa is a damaging bacterial pathogen in a number of countries around the world. Psa was provisionally identified in New Zealand on 5 November 2010 from a kiwifruit orchard in Te Puke. Subsequently the identification was confirmed and further infected orchards have been identified across the country, with a more virulent form of the disease being identified in the Bay of Plenty region. Unfortunately, the disease has continued to develop and progress rapidly and is now a very serious threat to the New Zealand kiwifruit industry. Significant effort is being invested to address the problem and there is now a considerable international research effort focused on Psa including a dedicated Plant & Food Research Psa research programme. The suite of projects reported here were established shortly after the Psa incursion occurred and were aimed at addressing immediate research needs. This report provides a summary of the research completed under the cap-stone project VI1175. Much of the information presented in this report has previously been reported to Zespri and provided to the industry.
Develop and implement an assay to asses if kiwifruit cambium tissue is living or dead, and apply this to kiwifruit tissue which has been heat treated.
Results from the bi-annual survey to look for genetic evidence of Psa adaption to Gold3 detected no significant changes in genes associated with Psa pathogenicity. An increase in new genetic elements that aid in conferring resistance to copper was observed.
Horizontal gene transfer can precipitate rapid evolutionary change. In 2010 the global pandemic of kiwifruit canker disease caused by Psa reached New Zealand. At the time of introduction, the single clone responsible for the outbreak was sensitive to copper, however, analysis of a sample of isolates taken in 2015 and 2016 showed that a quarter were copper resistant.
Genome sequences of seven strains showed that copper resistance along with resistance to arsenic and cadmium, was acquired via uptake of integrative conjugative elements (ICEs), but also plasmids.
Recurring epidemics of kiwifruit bleeding canker disease are caused by Psa. In order to strengthen understanding of population structure, phylogeography, and evolutionary dynamics, this project isolated Pseudomonas from cultivated and wild kiwifruit across six provinces in China.
Based on the analysis of 80 sequenced Psa genomes, we show that China is the origin of the pandemic lineage but that strain diversity in China is confined to just a single clade. Distinct independent transmission events marked introduction of the pandemic lineage into New Zealand.
Optimising copper use for sustainable control of Psa in kiwifuit orchards. This study was undertaken to build on previous work to develop best practice recommendations for protective sprays for kiwifruit. In particular, it was to determine (1) for how long low-drift air inclusion (AI) nozzles could efficiently deliver protectant sprays to expanding spring canopies, and (2) to maximise the efficiency of spray delivery to flowering Hayward and fully expanded Gold3 canopies on wide row spacings.
The advent of Psa in kiwifruit orchards has radically changed the way we need to think about kiwifruit growing practices to enable vines a greater chance of survival when challenged with the virulent strain of Psa (Psa-V). Vine structures in New Zealand have usually had a single trunk with one or two leaders as the primary framework upon which to carry the fruiting structure. Secondary infections of Psa-V in a leader, however, can have a major effect on vine productivity, with substantial loss of fruiting canopy beyond the canker if leaders need to be removed. In order to prevent catastrophic loss of productive canopy area when establishing top-worked kiwifruit vines exposed to Psa-V, we tested two methods of producing four-leader vines. Multi-leader trials with the new cultivars Actinidia chinensis Zesy002 (commonly known as Gold3), Zesy003 (commonly known as Gold9), A. deliciosa x A. chinensis Zesh004 (commonly known as Green14), an A. chinensis breeding selection, an A. deliciosa breeding selection, and the standard cultivar A. deliciosa Hayward, grafted to mature A. delicosa Bruno seedling stumps, have been established.
This project determined whether plant nutrition can influence the susceptibility of kiwifruit to Psa-V. By assessing the effect of soil nutrition and composition on the susceptibility of both Hayward and Hort 16A seedlings to Psa-V infection we were able to demonstrate that soil nutrition and co mposition can have a role in the susceptibility of seedlings to this pathogen.
A proof-of-concept study has been undertaken to assess the ability of the woody stem bioassay, a test developed by Plant & Food Research, to detect differences in response to Psa-V inoculation within Hort16A and Hayward kiwifruit vines from different orchards. Whilst the bioassay has been shown to detect differences in Psa-V resistance between genotypes and cultivars, it has yet to be tested as a determinant of varying resistance within a cultivar. Several orchards have been identified as part of this study that are free of Psa-V symptoms. The primary objective of this study was to determine if orchard-specific resistance to Psa-V can be detected using the woody stem bioassay.
The purpose of this trial was to determine the efficacy of Active Clean B used for sanitisation of surfaces.
The purpose of this trial was to determine the efficacy of Aussan L-44 used for sanitisation of surface.
In 2012, VLS undertook testing of various sanitisers on fruit contact and non-fruit contact
surfaces including wooden bin, plastic bin and metal and rubber etc to provide the industry with a measure of efficacy against Psa-V. This harvest season, 4 more products including two bio-gro certified products were tested to provide more sanitiser options effective against Psa-V to growers.
This trial tested 12 products for their efficacy as disinfectants against Psa. The aim was to provide practical advice to the industry for use where tools or equipment needs to be free from live Psa. It looks at the efficacy associated with both spraying and dipping (shallow immersion) for times from 10 seconds through to 2 minutes on 4 surfaces common within the industry.
Application of post-harvest Actigard® induced an upregulation of “defence marker“ genes in both Zesy002 (Gold3) and Hayward vines.
Gene expression patterns varied over time and differed between sites and cultivars. These patterns were consistent with Actigard® operating by upregulation of the salicylic acid defence pathway. This supports the value of applying Actigard® or copper plus Actigard® in the post-harvest window to help vines fight Psa infection.
Leaf health and integrity determined the level of vine response rather than the date of Actigard® application.
There was no evidence that the effects of post-harvest Actigard® application are carried over into the following spring.
This three-year project identified the Hayward flower bud growth stage(s) most susceptible to bud rot infection in the field, and the environmental conditions associated with these infections.
Infection ‘windows’ were created by covering vines to protect flower buds from rainfall and associated Psa inoculum and opening the covers for week-long ‘windows’ during sequential bud growth stages to allow natural infection to occur.
Early flower buds, which had just emerged in leaf axils and were still closed (approximately 3 weeks after budbreak), were the most susceptible to Psa infection. These buds remained susceptible to infection for 1-2 weeks after they first emerged.
Rainfall and the presence of orchard inoculum were identified as the key drivers of flower bud infection.
Psa is causal of Gold3 bud rot with flower buds susceptible to infection from a very early development stage i.e. from when flower buds have just emerged from the leaf axils are still closed and have yet to develop stalks. As for Hayward, infection appears to start on the outside of the flower bud and move in.
Surveys found significantly higher levels of bud rot for Gold3 on Bounty 71 rootstock (2-35%) vs Gold3 on Bruno rootstock (less than 1%). Bud rot incidence differed between sites and seasons with rainfall, site inoculum levels and timing of protectant sprays factors determining incidence.
Tank mixing of Kocide Opti with Proclaim did not affect Psa control. Emamectin residues were increased in the Kocide Opti + Proclaim mix, suggesting a positive chemical interaction which increased the longevity of the emamectin residue. Copper and emamectin residues were reduced 2-4 fold with the addition of Duwett®, but this was a physical effect of spray application via a hand sprayer.
None of the tank mixes showed reduced efficacy of the pest or disease control targeted. Prodigy (Brown Headed Leaf Roller), Luna Privilege (sclerotinia), Kocide Opti (Psa) and Actigard (Psa) were found to be compatible, as tank mixing of these products did not affect the efficacy of Prodigy against neonate Brown Headed Leaf Roller larvae or Luna Privilege against Sclerotinia.
It is not possible to protect strung vines from Psa with traditional airblast spray applications delivered from beneath the main pergola canopy. However, all three of the overhead spray delivery systems tested in these experiments, including the use of drones, could deliver higher deposits to the strung canopies than a standard airblast application.
The trial was established to determine the effects of an intensive autumn spray protection programme on Gold3 and Hort16A. It was difficult to separate treatment effects as the Gold3 site had little infection and the Hort16A site had too much infection. There was a trend for treatment programmes including a full programme with coppers, foliar applied elicitors and KeyStrepto™ to reduce the effects of Psa-V by comparison with other lesser treatment programmes.
Optimising copper use for sustainable control of Psa in kiwifuit orchards. This study was undertaken to build on previous work to develop best practice recommendations for protective sprays for kiwifruit. In particular, it was to determine (1) for how long low-drift air inclusion (AI) nozzles could efficiently deliver protectant sprays to expanding spring canopies, and (2) to maximise the efficiency of spray delivery to flowering Hayward and fully expanded Gold3 canopies on wide row spacings.
The project aimed to identify the primary cause of bud rot in green kiwifruit from orchards involved in a Psa spray programme trial. It is concluded that the majority of bud rot symptoms observed in this trial were the result of Psa infection.
This project was to assess the efficacy of Psa sprays against pre-flowering bud rot. To determine whether the recently observed bud rot was caused by Psa or other bacteria. To record any plant effects of the new Psa spray Ambitious.
This final report is a summary of key activities and outcomes over the past 15 months on a project designed towards testing on a commercial scale, a comprehensive spray programme, developed from results of previous trials, to minimise the impacts of Psa-V on orchard productivity.
There is a large range of products that have demonstrated some efficacy against Psa and are
now being widely used to protect kiwifruit vines. This study was undertaken to evaluate the
potential for such products to be tank mixed with products listed in the Zespri CPP. The
research reported here was carried out in two phases:
(1) a laboratory test to determine the physical compatibility of prioritised mixes
(2) a study on potted plants to evaluate potential phytotoxic effects resulting from tank
mixing products that were judged compatible in (1).
Chemical compatibility: 22 different spray mixes were tested as advised by Zespri. Each spray mix was shaken vigorously for 30 seconds, then photographed and the pH measured. The solution was observed for foaming, heat production, precipitates or phase separation of solution. After 30 minutes standing the solution was re-photographed, the pH remeasured and solution characteristics noted. Where any precipitates existed, the solution was shaken for a further 30 seconds to determine if the precipitate could be re-suspended. All spray mixes, except that of Nordox + KeyStrepto + Actigard, were deemed sufficiently physically stable to be further tested for phytotoxicity on kiwifruit foliage. It should be noted that physical stability does not necessarily mean that the products mixed are chemically compatible or chemically stable.
Zespri engaged HortEvaluation Ltd to undertake a trial to identify best practice agrichemical use for the autumn/winter period to protect kiwifruit vines from Psa infection and/or re-infection. In addition the trial explored whether forcing leaf fall by the application of copper sulphate, to shorten the leaf fall period, reduced the risk of infection during leaf fall compared with natural leaf drop.
The purpose of this trial was to investigate the efficacy of the stabilised chlorine
dioxide product Oxyspray 3000 for reduction in Psa-V inoculum, on Hort16A kiwifruit
leaves, using a standard orchard sprayer.
The effect of kiwifruit leaf expansion on protectant sprays has not been quantified to date. A project was undertaken to visualise how spray coverage changes on a leaf over a period of growth expansion, after application to newly emerged leaves. Because of the project timing (late autumn), rapidly expanding new foliage was not available on kiwifruit vines and so the rapidly-growing broadleaf, cotton (Gossypium hirsutum), was also investigated as a substitute leaf surface. Both kiwifruit and cotton leaves have similar moderately-easy-to-wet adaxial (upper) leaf surfaces.
This study was undertaken to compare three novel sprayer units (low volume Electrostatic, Silvan split air boom and Quantum Mist multi-headed axial fan) against an industry standard, axial fan, airblast sprayer (Atom), to determine if any of the novel sprayers could provide an incremental improvement in coverage of kiwifruit canopies with protectant sprays. The performance of the sprayers, with respect to spray coverage on foliage and spray distribution throughout the canopy, was compared on a pruned Hayward canopy containing dense, un-pruned male vines and a pruned Hort 16A pergola orchard, in early summer of 2011.
This study was undertaken to provide prescriptions for airblast application of protectant
sprays to kiwifruit at the spring canopy stage.
This study was undertaken to provide prescriptions for airblast application of protectant
sprays to kiwifruit at the dormant cane stage.
This study was undertaken to provide prescriptions for the aerial application of
protectant sprays to kiwifruit. In particular, to determine guidelines for low volume
aerial spray applications, using organosilicone superspreader adjuvants.
This three-year project identified the Hayward flower bud growth stage(s) most susceptible to bud rot infection in the field, and the environmental conditions associated with these infections.
Infection ‘windows’ were created by covering vines to protect flower buds from rainfall and associated Psa inoculum and opening the covers for week-long ‘windows’ during sequential bud growth stages to allow natural infection to occur.
Early flower buds, which had just emerged in leaf axils and were still closed (approximately 3 weeks after budbreak), were the most susceptible to Psa infection. These buds remained susceptible to infection for 1-2 weeks after they first emerged.
Rainfall and the presence of orchard inoculum were identified as the key drivers of flower bud infection.
Kiwifruit plants can often be infected with Psa but without symptoms. The time between infection and symptom development is known as the ‘latency’ phase. During that phase, infected plants are symptomless carriers.
It is extremely difficult to identify plants that are in a latency phase and to know how long the phenomenon can last. Understanding why an infected plant does not express symptoms and what are the triggers to break the latency phase (i.e. the triggers that will lead to the plant expressing symptoms) are important pieces of information that are needed to put in place strategies to prevent or manage outbreaks. A cover note summarising the report and results is available here.
Psa is causal of Gold3 bud rot with flower buds susceptible to infection from a very early development stage i.e. from when flower buds have just emerged from the leaf axils are still closed and have yet to develop stalks. As for Hayward, infection appears to start on the outside of the flower bud and move in.
Surveys found significantly higher levels of bud rot for Gold3 on Bounty 71 rootstock (2-35%) vs Gold3 on Bruno rootstock (less than 1%). Bud rot incidence differed between sites and seasons with rainfall, site inoculum levels and timing of protectant sprays factors determining incidence.
This three year project investigated the role of cold temperature and frosts in exacerbating Psa infection in New Zealand kiwifruit orchards. Observations included pre and post frost inoculation of detached canes (Hayward and Gold3), potted plants exposed to natural frost (Hayward and Gold3), and potted plants exposed to simulated frost (Gold3 only).
The study showed that severe winter frosts (below -6 degrees) can damage cold-hardened cane tissues and indicated the threshold for frost damage (which leads to greater Psa development) is around 24 frost degree hours (e.g. -6 degrees for 4 hours). Frost temperatures above -6 degrees did not damage dormant canes, but -10 degrees did cause damage. Psa lesion lengths were generally greater for Gold3 than Hayward, reflecting Gold3’s greater susceptibility to Psa cane infection and perhaps indicating lower frost tolerance than Hayward. Frost occurrence on already-infected canes, versus on canes infected immediately after frost, showed both had the same Psa development.
Findings from the work suggest that protecting dormant canes in response to mild frosts (for example by frost protection and/or copper applications) is not necessary, but for frosts below -6 degrees, copper application might reduce Psa infection and it doesn’t matter whether the copper is applied just before or just after a frost event.
The results of this work showed that Psa is present on both the outside of winter buds and within the buds themselves as they were expanding in the spring. The overall amount of Psa detected was low, however Psa was found more frequently from juvenile tissues from inside the buds (10.3%) than from the outside (5.1%). Consequently it appears that leaf spotting on the first expanding young leaves in the spring could be caused by either Psa from within the bud or Psa arriving on the expanding leaves.
A trial was undertaken by Kawerau-based Plateau Bark to see if compost could be made using reject fruit (and associated debris) mixed with pulp waste from the Norske Skog Tasman Ltd pulp and paper mill.
This project aimed to investigate orchard and management factors that may have been
associated with the level of bud rot experienced by kiwifruit growers, particularly growers of Green14, in the spring of 2012.
The objectives of the study were to describe the temporal, spatial and spatio-temporal spread of the bacteria Psa in kiwifruit during the outbreak in New Zealand.
To determine the risk of spreading Psa-V between kiwifruit vines via wound protectants or application tools used during grafting and pruning.
This project aims to determine long-term symptom progression and determine whether practices such as cauterising and partial cutting reduce the long-term impact of Psa.
Initial results from infected mature vines placed under plastic, breathable covering structures, indicated there is little to no reduction in the expression of disease relative to that observed in vines in uncovered areas. The trend observed in Canon Rd and Tuapiro Rd suggests that at this stage, the symptoms that are being exhibited in the vines undercover are still from the infections that occurred before the covers being erected. It will be critical to continue monitoring these plants to determine whether the symptoms of Psa infection will decline with potentially reduced inoculum levels likely to occur in the presence of the covers.
Pruning wounds probably provide multiple infection points for Psa-V and it is possible that some pruning methods pose greater risk of infection and canker development than others. The objective of this project was to confirm the degree of risk associated with a range of shoot pruning techniques normally applied in spring to ‘Hort16A’ and Hayward vines in the Bay of Plenty.
This project set out to try and quantify the levels of Psa-V in mulched plant material originating from heavily infected Hort16A vines. PCR employed a so-called third generation Taqman test and for plating we employed a new selective media which proved excellent under the difficult conditions i.e. high levels of non-target micro-fauna.
There is strong indication that the Psa bacteria can enter plants by colonising fresh pruning wounds. At this stage, there is little indication as to how long pruning wounds, or other sites of mechanical injury, remain susceptible to infection. Determination of the importance of pruning wounds as infection sites will affect a number of management decisions, such as timing of pruning, and necessity to protect cuts. This interim report describes an experiment carried out at Ruakura and Te Puke over the summer of 2011–2012 to assess the risks of summer pruning on Hort16A vines.
This study follows previous laboratory inoculation work that showed cicada egg-nests are a potential entry site for Psa infection. In this study, Psa infection of cicada egg-nests in canes of Actinidia cultivars Hort16A and Hayward was compared with adjacent, non-wounded canes to determine the potential role of egg-nest wounds in infection by Psa.
This project aims to map carefully and follow progress of Psa disease development within selected kiwifruit orchards and to provide answers to questions about the pattern and timing of spread within the canopy, and progression from leaf to secondary symptoms. Data collected could also be used to develop the relationship between weather events/environmental conditions and disease incidence and severity, and help to guide chemical control strategies.
Does Psa inoculum lodge on clothing, tools and vehicles? The aim was to identify key human/material vectors, to aid minimisation of orchard to orchard, and within-orchard, spread of Psa.
Canes of vines infected with Psa are becoming systemically infected and showing signs of dieback and other secondary symptoms. Canes are used for propagating new varieties of kiwifruit, and existing varieties. It is essential to find a method to ensure that propagating material is free of Psa, especially if a valuable irreplaceable new variety becomes infected by Psa.
There is evidence that canes of vines infected with Psa become systemically infected. Canes are used for propagating new varieties of kiwifruit, and existing varieties. It would be useful to find a method to ensure that propagating material is free of Psa, especially if a valuable irreplaceable new variety becomes infected by Psa. This research note reports on the first step (phase 1), which is to identify the thermal death point of the bacterial cells. Phase 2 will identify the thermal death point of the bacterial cells in budwood and the survival of budwood at temperatures that are lethal to bacterial cells.
Is Psa present in an historic collection of bacteria isolated from macerated kiwifruit buds, flowers and fruitlets from the Kumeu research orchard during spring 1991 (Everett & Henshall 1994)?
Results from the bi-annual survey to look for genetic evidence of Psa adaption to Gold3 detected no significant changes in genes associated with Psa pathogenicity. An increase in new genetic elements that aid in conferring resistance to copper was observed.
Previous research showed flower budrot loss due to Psa was more likely to occur and to a greater degree, on Gold3 grafted to Bounty 71 rootstock (Gold3-Bounty) than on Gold3 grafted to Bruno rootstock (Gold3-Bruno).
In this case study, the research results were used to model production and financial implications of three Gold3-Bounty Psa budrot scenarios versus the Gold3-Bruno result. “Moderate” (9%) and “least”(2%) Gold3-Bounty budrot scenarios achieved better returns than Gold3-Bruno.
Returns for the “worst” (35%) Gold3-Bounty scenario fell well below the Gold3-Bruno result. This suggests Gold3-Bounty can deliver improved returns, but results can be badly affected if Psa is not well managed.
This three-year project identified the Hayward flower bud growth stage(s) most susceptible to bud rot infection in the field, and the environmental conditions associated with these infections.
Infection ‘windows’ were created by covering vines to protect flower buds from rainfall and associated Psa inoculum and opening the covers for week-long ‘windows’ during sequential bud growth stages to allow natural infection to occur.
Early flower buds, which had just emerged in leaf axils and were still closed (approximately 3 weeks after budbreak), were the most susceptible to Psa infection. These buds remained susceptible to infection for 1-2 weeks after they first emerged.
Rainfall and the presence of orchard inoculum were identified as the key drivers of flower bud infection.
Psa is causal of Gold3 bud rot with flower buds susceptible to infection from a very early development stage i.e. from when flower buds have just emerged from the leaf axils are still closed and have yet to develop stalks. As for Hayward, infection appears to start on the outside of the flower bud and move in.
Surveys found significantly higher levels of bud rot for Gold3 on Bounty 71 rootstock (2-35%) vs Gold3 on Bruno rootstock (less than 1%). Bud rot incidence differed between sites and seasons with rainfall, site inoculum levels and timing of protectant sprays factors determining incidence.
Molecular analyses of microbial populations on diseased buds showed that Psa was the dominant species and that Psa was most likely the cause of bud rot. Girdling vines 30 days before flowering resulted in significantly less bud rot than in non-girdled vines. The effect was observed in both Hayward and Green14. The results suggest that girdling 30 days before bud break triggered a physiological response in the vine that limited the severity of bud rot.
The advent of Psa in kiwifruit orchards has radically changed the way we need to think about kiwifruit growing practices to enable vines a greater chance of survival when challenged with the virulent strain of Psa (Psa-V). Vine structures in New Zealand have usually had a single trunk with one or two leaders as the primary framework upon which to carry the fruiting structure. Secondary infections of Psa-V in a leader, however, can have a major effect on vine productivity, with substantial loss of fruiting canopy beyond the canker if leaders need to be removed. In order to prevent catastrophic loss of productive canopy area when establishing top-worked kiwifruit vines exposed to Psa-V, we tested two methods of producing four-leader vines. Multi-leader trials with the new cultivars Actinidia chinensis Zesy002 (commonly known as Gold3), Zesy003 (commonly known as Gold9), A. deliciosa x A. chinensis Zesh004 (commonly known as Green14), an A. chinensis breeding selection, an A. deliciosa breeding selection, and the standard cultivar A. deliciosa Hayward, grafted to mature A. delicosa Bruno seedling stumps, have been established.
Previous research showed flower budrot loss due to Psa was more likely to occur and to a greater degree, on Gold3 grafted to Bounty 71 rootstock (Gold3-Bounty) than on Gold3 grafted to Bruno rootstock (Gold3-Bruno).
In this case study, the research results were used to model production and financial implications of three Gold3-Bounty Psa budrot scenarios versus the Gold3-Bruno result. “Moderate” (9%) and “least”(2%) Gold3-Bounty budrot scenarios achieved better returns than Gold3-Bruno.
Returns for the “worst” (35%) Gold3-Bounty scenario fell well below the Gold3-Bruno result. This suggests Gold3-Bounty can deliver improved returns, but results can be badly affected if Psa is not well managed.
This three-year project identified the Hayward flower bud growth stage(s) most susceptible to bud rot infection in the field, and the environmental conditions associated with these infections.
Infection ‘windows’ were created by covering vines to protect flower buds from rainfall and associated Psa inoculum and opening the covers for week-long ‘windows’ during sequential bud growth stages to allow natural infection to occur.
Early flower buds, which had just emerged in leaf axils and were still closed (approximately 3 weeks after budbreak), were the most susceptible to Psa infection. These buds remained susceptible to infection for 1-2 weeks after they first emerged.
Rainfall and the presence of orchard inoculum were identified as the key drivers of flower bud infection.
Psa is causal of Gold3 bud rot with flower buds susceptible to infection from a very early development stage i.e. from when flower buds have just emerged from the leaf axils are still closed and have yet to develop stalks. As for Hayward, infection appears to start on the outside of the flower bud and move in.
Surveys found significantly higher levels of bud rot for Gold3 on Bounty 71 rootstock (2-35%) vs Gold3 on Bruno rootstock (less than 1%). Bud rot incidence differed between sites and seasons with rainfall, site inoculum levels and timing of protectant sprays factors determining incidence.
This three year project investigated the role of cold temperature and frosts in exacerbating Psa infection in New Zealand kiwifruit orchards. Observations included pre and post frost inoculation of detached canes (Hayward and Gold3), potted plants exposed to natural frost (Hayward and Gold3), and potted plants exposed to simulated frost (Gold3 only).
The study showed that severe winter frosts (below -6 degrees) can damage cold-hardened cane tissues and indicated the threshold for frost damage (which leads to greater Psa development) is around 24 frost degree hours (e.g. -6 degrees for 4 hours). Frost temperatures above -6 degrees did not damage dormant canes, but -10 degrees did cause damage. Psa lesion lengths were generally greater for Gold3 than Hayward, reflecting Gold3’s greater susceptibility to Psa cane infection and perhaps indicating lower frost tolerance than Hayward. Frost occurrence on already-infected canes, versus on canes infected immediately after frost, showed both had the same Psa development.
Findings from the work suggest that protecting dormant canes in response to mild frosts (for example by frost protection and/or copper applications) is not necessary, but for frosts below -6 degrees, copper application might reduce Psa infection and it doesn’t matter whether the copper is applied just before or just after a frost event.
Inocbloc and copper paste confirmed to show efficacy for protecting wounds. However, neither product should be used on grafts (death of potted plants) or girdles. Abnormal swelling above the girdle was observed.
Molecular analyses of microbial populations on diseased buds showed that Psa was the dominant species and that Psa was most likely the cause of bud rot. Girdling vines 30 days before flowering resulted in significantly less bud rot than in non-girdled vines. The effect was observed in both Hayward and Green14. The results suggest that girdling 30 days before bud break triggered a physiological response in the vine that limited the severity of bud rot.
Increased concentrations of procyanidin polyphenol metabolites were found in leaves from root pruned vines taken 2 days after root pruning but not at subsequent sampling times. This response was associated with root pruning. We found no evidence for an effect of Actigard™ on the procyanidin metabolism in leaves. The procyanidin response to root pruning is similar to that observed by us in previous trunk girdling experiments with Hort16A Actinidia chinensis var. chinensis Hort16A and A. chinensis var. deliciosa Hayward vines, and by others studying metabolic responses of plants to stress. This work has helped elucidate a key metabolic response to wounding in kiwifruit that may be implicated in disease response. Further work is underway.
The results of this work showed that Psa is present on both the outside of winter buds and within the buds themselves as they were expanding in the spring. The overall amount of Psa detected was low, however Psa was found more frequently from juvenile tissues from inside the buds (10.3%) than from the outside (5.1%). Consequently it appears that leaf spotting on the first expanding young leaves in the spring could be caused by either Psa from within the bud or Psa arriving on the expanding leaves.
Trials were set up in the kiwifruit growing season of 2012–13 on three orchards to test whether plastic, breathable covers erected over existing kiwifruit vines could reduce the incidence, progression and severity of Psa infections. These structures had been erected in an attempt to slow the progression of Psa. Vines were already infected with Psa, with varying levels of symptoms expressed. Across the three sites the varieties Actinidia chinensis Zesy002 (Gold3), A. chinensis Zesy003 (Gold9), A. deliciosa Zesh004 (Green14) and A. chinensis Hort16A were assessed, along with Gold3 scions that had been notch grafted onto existing rootstocks. Grafted seedlings were planted out at each site and used as trap plants that would indicate infection from Psa.
Green orchards, male vigour, management techniques.
Girdling of Hayward and Zesy002 (commonly known as Gold3) orchards was undertaken in the season of 2012-13. Girdling treatments were imposed on these vines and observations were made for leaf and secondary symptoms caused by Psa-V on the vine. At the time of girdling, cores were taken from a subset of the vines treated to establish a baseline incidence of Psa within the vines in the experimental area. At the conclusion of the trial, vines were cored for DNA analysis to determine whether Psa was present. A Zesy003 (Gold9) orchard was also observed, however, no baseline Psa incidence was recorded. Girdling was undertaken by the orchardist and assessments for the presence of Psa were performed post-girdling. Results for this work indicate the vines in which the girdles heal are less likely to be infected by Psa than vines where girdling has been too deep and the wounds have not healed. In non-healed girdles, Psa was generally present. Care in the course of girdling is important so the wounds heal rapidly and Psa infection via this entry point is minimised.
This project aimed to investigate orchard and management factors that may have been
associated with the level of bud rot experienced by kiwifruit growers, particularly growers of Green14, in the spring of 2012.
Zespri engaged HortEvaluation Ltd to evaluate products with demonstrated efficacy against Psa leaf spot over the leaf fall period. The trial was established at two sites with Gold3 and Hayward vines in the Bay of Plenty, within Psa recovery zones.
This project aims to determine long-term symptom progression and determine whether practices such as cauterising and partial cutting reduce the long-term impact of Psa.
Girdling techniques are used extensively in the kiwifruit industry and are fundamental to achieving high productivity (yield and high dry matter) in both Hayward and Hort16A orchards. However, girdling results in significant wounds either on the trunk or on the canes. Based on knowledge of other Pseudomonas species infecting perennial fruit crops, it was anticipated that the wound sites created by girdling of kiwifruit vines may present a significant point of infection for Psa.
This project aims to map carefully and follow progress of Psa disease development within selected kiwifruit orchards and to provide answers to questions about the pattern and timing of spread within the canopy, and progression from leaf to secondary symptoms. Data collected could also be used to develop the relationship between weather events/environmental conditions and disease incidence and severity, and help to guide chemical control strategies.
Systemic application of antibiotics, elicitors and other compounds into kiwifruit vines is seen as one possible method of combating Psa. This poses the question, “which is the most effective trunk delivery method?”
Treatments to limit the spread of Psa in orchards are required. Etec have requested preliminary in vitro testing of three products for activity against Psa.
Treatments to limit the spread of Psa in orchards are required. Etec have requested preliminary in vitro testing of three products for activity against Psa. This document reports on the growth rate testing of two of those products.
Growers urgently require information relating to the relative risk of infection that key orchard/vine management techniques create. One example of this is girdling. Anecdotal observations from offshore and New Zealand have suggested that the practice of girdling does not increase the risk of Psa-V infection. In-fact the expression of internal staining symptoms has been inhibited at the point of cane girdles.
The bacterial plant disease Psa is a damaging bacterial pathogen in a number of countries around the world. Psa was provisionally identified in New Zealand on 5 November 2010 from a kiwifruit orchard in Te Puke. Subsequently the identification was confirmed and further infected orchards have been identified across the country, with a more virulent form of the disease being identified in the Bay of Plenty region. Unfortunately, the disease has continued to develop and progress rapidly and is now a very serious threat to the New Zealand kiwifruit industry. Significant effort is being invested to address the problem and there is now a considerable international research effort focused on Psa including a dedicated Plant & Food Research Psa research programme. The suite of projects reported here were established shortly after the Psa incursion occurred and were aimed at addressing immediate research needs. This report provides a summary of the research completed under the cap-stone project VI1175. Much of the information presented in this report has previously been reported to Zespri and provided to the industry.
Two studies were undertaken to determine (1) how rainfall affects residues of commercial
copper sprays on Hort 16A and Hayward dormant canes (both old and replacement wood) and (2) how rainfall affects residues of organic copper + oil sprays on Hayward replacement canes.
Inocbloc and copper paste confirmed to show efficacy for protecting wounds. However, neither product should be used on grafts (death of potted plants) or girdles. Abnormal swelling above the girdle was observed.
Inocbloc and copper paste consistently protected pruning wounds on kiwifruit vines from infection by Psa-V, in both potted plant trials and in the field.
The purpose of this trial was to carry out an invitro study of Psa survival in wound protectant (PruneTec).
Wound protection continues to be a challenge for kiwifruit growers since the incursion of a virulent strain of Psa in New Zealand in November 2010. When several products were tested in the field as wound protectants against natural infection by Psa, there were no significant differences between treatments (Miller et al. 2012). Therefore, there is demand in the kiwifruit sector for a wound protectant suitable for pruning wounds. This project evaluates a range of registered treatments not previously tested for protecting pruning wounds against Psa and explores the use of a penetrant for driving the product into the wound to provide protection in the case of bacteria entering the plant during the cutting process.
This study examined the efficacy of a number of wound protectants alone and in combination with other bactericides.
To determine the risk of spreading Psa-V between kiwifruit vines via wound protectants or application tools used during grafting and pruning.
Zespri engaged HortEvaluation Ltd to evaluate a number of elicitor and copper products that may reduce Psa infection over the leaf fall period.
The trial was established at two sites with suitable Gold3 and Hayward vines in the Bay of Plenty, within Psa recovery zones.
The elicitor products included single applications of Actigard, BioAlexin and Spotless prior to leaf fall. The copper products included Nordox or Cuprofix Disperss, each applied twice over the leaf fall period.
The trial was carried out as intended, except that air frosts voided the opportunity to include copper sulphate to force leaf fall on some treatments. No other leaf fall protectant products were applied by the respective growers over the leaf fall period.
Buds and leaf scars were excised at the end of leaf fall, laboratory plated and cultured to detect Psa presence. Treated vines were assessed while dormant in late winter; and in spring after bud break, for presence of Psa symptoms ooze, cankers and cane dieback.