Selection of Superior Biological Control Agents with Genetic and Cultural Criteria
U.S. Arid Land Agricultural Research Center
2012 Annual Report
1a.Objectives (from AD-416):
Determine selection criteria for next generation atoxigenic biological control agents through development of laboratory and population based assays and criteria. Delineate both association of specific fungal groups with target crops and genetic characteristics of value in monitoring fungi of interest and in selecting elite biocontrol fungi.
1b.Approach (from AD-416):
Apply genetic methods to identify unique biological control agents and to associate specific fungal genetic groups with target crops and regions. Develop pyrosequencing assays to monitor specific fungi in the environment and during host infection. Utilize genomic approaches to identify traits of potential value in selecting next generation biological control agents for aflatoxin mitigation. Use crop based assays to rank relative desirability of atoxigenic strains for use in target agroecosystems.
Both laboratory and field studies aimed at selecting next-generation atoxigenic biocontrol strains were conducted. Pyrosequencing assays were developed to detect and measure frequencies of specific genotypes in host tissues and environmental samples (i.e. soil). Pyrosequencing assays were used to monitor responses of different Aspergillus (A.) flavus genotypes to a variety of biological (i.e. host) and environmental (i.e. temperature, nutrients) parameters. Influences of crop host species on competitive success of diverse A. flavus genotypes were detected and hosts were found to differentially influence sporulation by competing isolates during host infection. This influence resulted in skewed distributions of isolates within the pools of spores produced on infected crops. Such influences on sporulation are one mechanism through which hosts shape the populations of associated fungi. Another mechanism is direct influences on the extent to which mycelia of infection isolates invade host tissues. Isolates clearly differed in ability to ramify through hosts and these differences varied for corn, soybean, cottonseed, and sorghum. Data obtained from laboratory studies is currently being used to develop criteria for screening and selection of elite atoxigenic biocontrol strains for diverse agroecosystems. Specific selection criteria developed from these studies include superior competitive ability on both target and rotation crops and superior ability to sporulate during infection of target crops. The utility of laboratory assays in screening for premier atoxigenics will be validated in field studies. Genomic approaches for identification of traits of potential value in selection of next generation biological control agents have not yet been utilized, but it is anticipated that whole genome sequencing of multiple atoxigenic isolates of A. flavus will be undertaken in the near future. The overall project is making significant contributions to understanding and optimizing biological control with atoxigenic strains. This project directly contributes to Objective 1, Advance biocontrol technologies through strain selection, formulation, and adaptation to agronomic practices, and Objective 2, Characterize adaptive differences among Vegetative Compatibility Groups and strains of Aspergillus flavus including adaptation to host, environment, and ecosystem, of the parent CRIS.