1a. Objectives (from AD-416)
1. To explore improvements to formulation of biocontrol yeast for field application by growers. Types of formulations are wet formulations with additives (preservatives, nutritional supplements, surfactants for spreading) and dry formulations for delivery of viable yeast as a dry powder for tank mixing. 2. Evaluation of yeast longevity under different storage and application conditions: time and temperature. 3. Application for controlling l of other microbial pathogens: plant pathogenic fungi, microbial contaminants of crops (Salmonella, E. Coli)
1b. Approach (from AD-416)
Objective 1. Protective additives will be added to wet and dry yeast formulations and evaluated for improved shelf-life under lab conditions. Spray trials in the field will be used to evaluate effects on durability on plant leaves and fruits. Surfactants will be in the tank mix for even spreading. Objective 2. Yeast durability in a fully diluted mixture will be evaluated through time and temperatures series in lab so the upper threshold that might be expected under grower conditions. Objective 3. Ability to control fungi on agricultural crops. evaluations will be done using greenhouse tests on plants and pathogens of significance in tree fruit-nut and vegetable crops. Salmonella is a particular problem on almond. Initial experiments will involve field sprays on almond followed by collection of nuts and inoculation with Salmonella in lab-greenhouse and monitor Salmonella population. Non-pathogenic E. Coli strains applied to lettuce and spinach in the greenhouse followed by yeast spray applications to determine whether potential control is possible. The effectiveness of the yeast against additional fungi of agricultural importance will initially be evaluated on tomato and potato. Documents SCA with UC-Davis.
3. Progress Report
Saprophytic yeast, Pichia anomala has been demonstrated to inhibit the growth of Aspergillus flavus as well as aflatoxin production by this fungus. It was also shown to inhibit Alternaria spp, Penicillium spp, Botrytis spp in lab assays. A stable liquid formulation is highly desirable because most of the bicontrol yeast products are dispersed in water and delivered by spraying or dipping to the agricultural and horticultural crops. A wet formulation to store the yeast cell in refrigerator for prolonged shelf life is in progress. The growth medium can produce 5 to 10 billions of cells per ml in a matter of three day. This amount of yeast cells can be diluted 100 to 1,000 fold for field sprays. Field trials are ongoing to control Alternaria disease in pistachio orchard. Because disease potential of Alternaria was low in 2008, the effect of Pichia anomala on Alternaria disease control could not be evaluated. A new strategy to flood the orchard floor will be adapted to create a humid environment in favor of Alternaria disease development. Two sprays of yeast cells were applied on June 11 and June 25, 2009, and two more sprays were planned for August, 2009. Pistachio nuts will be harvested in early September to evaluate nut yield. Alternaria disease symptom on pistachio trees will be examined. Pichia anomala was tested as a biocontrol agent to reduce the survival and growth of E. coli. Attenuated E. Coli 015:H7 strain was applied to spinach plants kept in a quarantined greenhouse. Preliminary results indicate that Pichia anomala reduced the number of E. coli on the spinach. Additional experiments are planned. The ADODR monitored this project through site visits, emails and phone calls.