Improving basil downy mildew control with cultural and biological methods

Improving basil downy mildew control with cultural and biological methods

Summary

The goal of this research is to approach basil downy mildew disease control by defining the pathogen biology for effective and precise cultural control, as well as testing a biological control treatment. Basil downy mildew is caused by the pathogen Peronospora belbahrii, which results in devastating crop losses for basil growers. Basil downy mildew is not effectively controlled with organic fungicide spray programs, and conventional fungicides are limited and can risk increased pathogen resistance. We are working toward determining how long the basil downy mildew pathogen remains viable and infective so that we can develop a recommendation regarding how soon crops may be re-established in a greenhouse following a disease episode. We are also investigating the biological control efficacy of Pseudozyma aphidis, a filamentous yeast closely related to biological control agent Pseudozyma flocculosa. In order to determine this organism’s capability of reducing basil downy mildew infection and spread, we are using disease scoring methods, microscopic examination of the extent of P. belbahrii hyphal infection in sweet basil, and quantitative real-time polymerase chain reaction (qRT-PCR) of basil downy mildew biomass reduction resulting from treatment with P. aphidis.

Objectives/Performance Targets

There are two main experimental objectives for this research, as follows:

• Determine the length of time that Peronospora belbahrii sporangia remain viable in order to establish a safe time interval at which time greenhouse basil production can be re-established after a disease episode has occurred.
• Determine the efficacy of Pseudozyma aphidis applied as a biological control to reduce basil downy mildew infection.

As of December 2016, we have established our inoculation system for producing consistent infection. After trialing the use of a tween surfactant mixed with the inoculum, as proposed in the grant application, we did not find significantly different infection results, and so we will be using sporangial suspensions in sterile deionized water for all inoculations moving forward. We are currently optimizing our protocols for collection of P. belbahrii sporangia, application of Pseudozyma aphidis, and molecular quantification of P. belbahrii in infected plant tissue in order to assess disease severity. We will begin the first P. aphidis efficacy trials in early January 2017, and collect tissue from this inoculated batch to utilize for molecular quantification. The P. belbahrii sporangia viability assays will begin in mid-January 2017.

Accomplishments/Milestones

     During the Fall of 2016, we have established a reliable and consistent inoculation protocol, identified and set-up our experimental design and materials, and have identified candidate genes for quantitative molecular assessment of P. belbahrii in infected basil tissue. The initial work on identification of candidate genes for assessing basil downy mildew infection was presented during the Northeastern Division of the American Phytopathological Society Annual meeting in Ithaca, NY, in October. We were also able to discuss experimental methods with other plant pathologists and gain some new insight into handling of the pathogen infective structures in order to fulfill objective one in the event that we need to troubleshoot the experimental design.

     This winter we are beginning the disease rating of plants treated with P. aphidis to determine biological control activity, and we are optimizing the collection of P. belbahrii sporangia for objective one. We had an interruption in our work timeline this Fall due to an unforeseen shortage in plant material following a pest outbreak in a shared propagation greenhouse, but we have since been able to control the problem and generate new plant material to start working with in January. So far, we have been able to troubleshoot any problems that arise with the experiments, and we anticipate being able to produce our first sets of quantitative data for the biological control trial based on disease scoring by mid-January.

Impacts and Contributions/Outcomes

Once our aims are completed, we intend to report the results in one or two UMass Extension publications, and the research will be directly communicated with growers during a UMass Extension Field Day and a Basil Workshop held at the 2017 New Jersey Agricultural Convention & Trade Show. If the data is promising for either or both objectives, we will work toward publishing the research in a peer-reviewed journal so that other researchers may build upon it if so inclined. Our work with objective one, the assessment of P. belbahrii sporangia viability, is particularly important for sustainable agriculture practices in controlling basil downy mildew because our results will reveal a piece of information regarding cultural control of the pathogen that is yet unknown. This data can be used by growers to inform their re-entry period for re-establishing basil crops in greenhouses with previous downy mildew outbreaks. If the data for objective two suggests that P. aphidis is effective as a biological control against P. belbahrii, then this organism can be developed as a marketed treatment.

Collaborators: