2008 Annual Report
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.
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, Penicilum spp, Botrytis spp in lab assays.
Formulation of biocontrol yeast is very important for prolonging the shelf-life of the yeast product and enhancing biocontrol activity in field application. A wet formulation to store the yeast cell pastes at 40C in saline and glycerol solution has been used for field experiments. Additives such as lactose, glycerol, and trehalose were demonstrated to prolong the shelf life of yeast cells in wet paste. Encapsulation of the yeast cells in bio-polymer is in progress.
Yeast cells suspended in tank water were monitored for viability by determine the CFU (colony forming unit) on nutrient agar. The viability of yeast cells was not affected at 300C for several hours in water suspension. There was slight decline in viability when the tank water temperature was 350C in 2 hours.
Field trials are ongoing to control Alternaria disease in pistachio orchard. Air samples were taken after yeast spray in orchard. Preliminary results showed the sprayed yeast cells were not detected in the surrounding air. Green-house experiments are being set up at UC Davis to control Alternaria spp infecting pistachio, potato and tomato by Pichia anomala. The ADODR monitored this project through site visits, emails and phone calls.