- Nuts: general nuts
- Education and Training: on-farm/ranch research
- Pest Management: biological control
This project consisted of three activities. 1) A biocontrol yeast, developed by USDA-ARS (WRL-076) was tested to determine whether it could survive in the field long enough to serve as a control agent for Alternaria alternata. 2) The ability of the yeast to control A. alternata in the field was evaluated with a replicated test against a water control. Efficacy was evaluated from counts of damaged fruit clusters and marketable yield. The effect of the yeast on other nut micro-organisms was also evaluated. 3) Additional yeast strains were tested using a plate challenge test followed by scratch tests in the greenhouse.
Two years of sampling (in-husk nuts were evaluated) were conducted to determine whether the yeast would persist in the field for a sufficient time period to provide protection against A. alternata infection. Adequate levels of residual yeast remained on the nuts after 17 days throughout the growing season.
Commercial scale yield trials were conducted over 4 years. Significant A. alternata epiphytotics were observed in 2006 and 2009, but environmental conditions prevented A. alternata development in 2007 and 2008. The yeast produced about 14% higher marketable yield in 2006 and 2009 and no detectable difference in 2007 and 2008. However, these difference were not statistically significant due to high levels of uncontrollable variation. Nut cluster damage was also evaluated and treatment effects for this measure of A. alternata infection was highly significant (P=0.001), due to the large number of error df for this study. Cluster damage was also moderately correlated (r=0.47, P=0.002) with yield differences.
Two additional yeasts strains were selected for controlled greenhouse testing against both A. alternata and A. solani. A. alternata was evaluated on pistachio while A. solani was evaluated initially on tomato and later on potato using leaf scratch tests. High levels of uncontrolled variation were present and significant differences from water controls or from WRL-076 were not established.
The WRL-076 yeast was found to be an effective control measure on a waterborne bacterium, Burkholderia cepacia, a contaminant in the spray feedwater in 2007.
Project objectives:div style="margin-left:1em;">
1. Evaluate biocontrol yeast that has been released by USDA-ARS.
2. Test additional biocontrol yeast strains that have shown particular efficacy against multiple A. alternaria strains found on pistachio.
3. Test promising strains from objective 2 in the greenhouse and field.
Objective 1 was the major focus of the project Our central objective has been to test the efficacy of a specific strain (WRL-076) of Pichia anomala that was isolated from the natural environment (a pistachio orchard) for control of Alternaria alternata at a field scale in an organic production environment where possible interaction effects from prior pesticide sprays are absent. Four years of data were collected for yield and fruit cluster survival. Additional strains were screened for ability to inhibit A. alternata on culture plates and the best 2 were selected for greenhouse tests with pistachio (A. aternata) and potato and tomato (A. solani). Additional data was collected to determine the effect of the field sprayed yeast on other micro-organisms found on the nuts.