SFF Project Summary
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| Quarterly Update: | October 2006 |
| Updated: | 08 December 2006 |
The goal of this project is to determine whether bacteriophages can be used to control: Xanthomonas campestris pv. juglandis (X. c. juglandis) the causal agent of bacterial blight on walnut.
Previous studies carried out in New Zealand indicate a high level of variability between strains of X. c. juglandis as regards to their susceptibility to bacteriophages. This variability means that it is necessary to establish a collection of strains of the pathogen that are present in New Zealand. Such a collection has been established. It comprises strains previously isolated by Lincoln University and 15 new strains isolated from samples of walnut fruits from different cultivars showing symptoms of bacterial blight that were sent from five different regions of New Zealand.
Of the collection held by Lincoln University, a total of 72 strains tentatively identified as Xanthomonas sp. by their morphology on selective agar plates, have been recovered.
Bacteriophages isolated previously and held by Lincoln University were also received. Ninety per cent (19 out of 21) of the tubes harbouring phages yielded live bacteriophages that could produce plaques on X. c. juglandis strain 134 or X. c. juglandis strain 80. The ability of these bacteriophages to lyse the new strains of X. c. juglandis isolated from New Zealand will be tested next.
Quarterly Update: October 2006
In the 4 months to 30 Oct 2006, experiments have been conducted on cabbages to ‘screen’ a range of possible substitutes for mankcoide, or alternative chelators to mancozeb to add to copper hydroxide. The plans are described in the document entitled “ cabbage as a model system” and the results in “Cabbage as a Model System Write Up” both of which are appended.
In summary, it was found that methionine and aminofit were potential substitutes and worthy of inclusion in the walnut spraying trial. During the course of conducting this experiment it was also discovered that the proprietary copper hydroxide + mancozeb mixture is not formulated to provide an equal number of moles of the two compounds. Since we believe the success of the mixture lies in the chelation of the CuOH by the mancozeb, a mole of mancozeb is required for each mole of CuOH. Thus, experiments will be conducted with the mancozeb fraction increased to provide a mole of mancozeb for each mole of CuOH.
Experimental plans have also been written for the spraying trails. There are appended. The experiments have commenced, this has included budburst spraying and initial in-season sprays of walnut trees in the major objectives (Objectives 1 and 2) and the preparation of seedlings and bacterial cultures for the cabbage as a model system experiments (Objective 3). The experiments investigate the effectiveness of climate indices for predicting optimal spray timing and the use of alternatives and additives for copper spray types.
Experimental plans have also been written for the in-vivo trials with phages, these are appeneded. These experiments start in mid Nov 06.
There will be a field day on 26-11-06 on spraying technologies where David Manktelow will describe appropriate rates and concentrations to use. How to tune and monitor sprayers and other practical necessities for effective spraying. There nwill also be a demonstration of spray application by helicopter to compare with spray application from ground-based rigs.
Also appended to this report is an overall report against milestones for the project to date.
June 2006
In the quarter to 30 June 2006, the results from the spraying trials for the 2005-2006 season have been further analysed and an updated report is appended. Trails have commenced with inoculating cabbages and then testing a range of chelators which we hope will be able to replace the “somewhat nasty” ditiocarbamate which is added to the (not very effective) Copper Hydroxide to make the (much more effective) Mankocide. Initial report appended.
We held a field day on 28-5-06 where this season’s results were presented to the Industry Group. The session was well attended and good discussion of blight management followed.
For the phage work, it appears that hortresearch now have a bioassay technique which involves using walnut leaves. They will be in a position to do extensive phage testing next season once walnut leaves are available.
March 2006
In the quarter to 31 Mar 2006, the measurements for the spraying experiments have been completed and analysed. Levels of kernel damage correlate well with disease symptoms visible on husks in January. The results show a clear ordering of levels of disease control with fortnightly spraying>climate triggered sprays>no spraying. The results also demonstrate the importance of budburst spraying.
In the forthcoming quarter, trials will be conducted to try to find a replacement for the dithiocarbamate (mancozeb) which is used as an additive to Copper Hydroxide (Kocide) to make mankocide. Our trial work (and that of our collaborators in Tasmania) has shown mankocide to be significantly more effective than kocide. The essential difference is that mankocide contains a dithiocarbamate which acts as a chelator and makes the copper more bio-available for pathogen control. However, the dithiocarbamate has several environmental and customer-perspective downsides and so the search for a more suitable replacement is motivated.
Representatives from the team visited our collaborators in Tasmania in February. Experimental conditions and results were compared which was a valuable exercise. Representatives from Tasmania will visit New Zealand in the forthcoming quarter.
The phage research has progressed during the quarter with HortResearch making good progress in developing a bioassay for walnut blight. Walnut leaflets were inoculated with the pathogen and the disease developed. We need to be confident that this bioassay is sufficiently representative of the biological processes that occur in-vivo before proceeding to use it as a testbed for phage-based control methods of the pathogen.
The field day to disseminate recent results was deferred from March until our AGM day in May. This will enable a complete set of results for the season to be presented and is more efficient for NZWIG members to be able to learn about the research results whilst attending the AGM.
September 2005
In the quarter to 30 Sept 2005, the results from last year’s trials have been fully analysed and disseminated to growers through newsletter articles etc. We have prepared a set of experimental plans for the forthcoming season which have already started as we have had bud burst at the trial sites.
We will be experimenting with timing of bud burst sprays and the value of repeated sprays at bud burst. This will be measured both by blight in nuts later in the season but also in blight bacteria population counts taken after bud burst going into the main part of spring.
We will again focus on smart timing of the sprays during the season and believe we have ‘learned’ what modifications may be needed to the Californian climate based decision support model. We will be trialling the use of Aminofit to help manage blight, this has shown some promise in previous work.
The phage team are currently focused on finding a suitable ‘bioassay’ on which the first non-lab trials of phages can be conducted. To date, all trials have been done in laboratory environments such as Petri dishes where the phages have been able to deactivate the bacteria. The next phase is to move to an environment which more closely resembles a walnut orchard. Options being considered include small walnut trees in a glasshouse and branches off walnut trees kept alive under controlled conditions.
During the forthcoming quarter, much of the experimental work will be undertaken. A ‘Spraying technologies’ field day is also planned to provide growers more insight into the equipment most suited for blight management.
to June 2005
In the quarter to 30 June 2005 we have been harvest-time assessments of the treatments for the season and have been reviewing and analysis the data for the 04/05 season. We are preparing an article for Walnut Growers describing what we believe to be best practice and what we think the likely effects of deviations for this are… e.g. if you spray 6 times instead of 3 then it will cost you this much more and have this environmental impact for this much more revenue ..etc). This article will be timed to coincide with the start of the new season, spraying starts in late Sept so we will probably put this article out in late Aug.
We have been communicating regularly and constructively with our collaborators in Tasmania and have been having phone conferences every 6 weeks or so through the off season when most of the work is office-based analysis and planning.
The transfer of the phage and bacteria (pathogen) collection from Lincoln University to Hort Research has taken place and the Hort Research team are now confirming that we have an effective taxonomy for the strains of the pathogen and phages and will move on to confirm the matrix of which of the phages kill which of the bacteria.
The results currently available from the contractors are appended along with a progress report on the phage work.
31 March 2005
In the quarter to 31 March 2005 we have been making observations on the blight levels in the trial trees following the treatments which were substantially applied in the previous quarter with a few sprays still applied in early January. We held a field day for the WIG research committee in mid January when Tim Jenkins taught us the ‘standard’ method he has developed for estimating what proportion of nuts are affected by blight. This was a very useful session and we now have a team of people who can make a ‘standardised’ assessment of blight incidence. Mid January is the best time to assess blight as most of the symptoms which are gong to appear have appeared by then and few of the blighted nuts which are going to abort have aborted by then. So, earlier assessments can give low scores as some symptoms have not yet appeared and later assessments can give low scores as some blighted nuts have aborted. Our intention is to teach persons involved in the benchmarking programme this method so we can get a broad set of data showing blight incidence and we can compare this to management inputs/decisions etc. We will do this teaching just prior to mid January next season in time for benchmarking assessments.
A visit was made to Tasmania by members of the WIG research committee and Tim Jenkins to meet our collaborators in February. We visited their trial sites and discussed the experiments being conducted there. We also met up with their contractor form TIAR to discuss the epidemiology work. A return visit was made by members of the Tasmanian team in early march and a field day was held to discuss the results with growers.
