2012 Annual Report
1a.Objectives (from AD-416):
To identify corn germplasm with resistance to Aspergillus flavus infection and aflatoxin accumulation and to identify genes associated with resistance.
1b.Approach (from AD-416):
A panel of 300 corn inbred lines have been crossed with a common tester line. The resulting testcrosses will be evaluated for aflatoxin accumulation at locations in Texas and Mississippi. An association mapping analysis of genotypic and phenotypic data will be conducted to identify alleles associated with resistance to Aspergillus flavus infection and aflatoxin accumulation.
Aflatoxin contamination in maize (Zea mays L.) grain is caused by the fungus Aspergillus (A.) flavus Link:Fries. Because aflatoxin is a carcinogenic mycotoxin with severe risk to animal and human health it is federally regulated in the United States. This important regulation limits marketability and causes disproportionate economic losses to southern maize producers. Plant breeding for decreased susceptibility is the most economic and practical method of reduction, however, no reported elite germplasm carries full resistance to aflatoxin accumulations. Furthermore, most commercial varieties are highly susceptible to A. flavus infection and toxin accumulation. Our primary objectives were to breed several different germplasm sources (including both developing new lines and corresponding hybrids for testing) for aflatoxin accumulation in multiple environments and to evaluate yield of these hybrids which is the single largest barrier to adaptation of aflatoxin resistant material. Yield and agronomic data were collected on over 1,215 hybrids in Texas. In College Station, Weslaco, and Ganado, TX, these tests were planted at the standard time, under standard well watered conditions and included multiple tests, two replicates of either two row or one row plots (primarily based on seed availability). In Corpus Christi, these hybrids were planted late and under dryland conditions to induce aflatoxin and drought stress as one row plots with three replications. The tests included both new hybrids in their first season (~788-CS; 338-WE; 14-GA) as well as hybrids being tested for a second year and inoculated with A. flavus (~277-CS; 99-WE; 39-CC; 26-GA) - numbers may not sum to total because of difficulty in categorizing material and various fill and check plots. Corn kernels colonized by toxigenic A. flavus were spread between rows at silking for all second year yield trials (CS, WE, CC). Although similar to delivery of atoxigenic strains by growers, this method differs in that conidial inoculum is immediately available for colonization of silks. Subsamples of grain were collected at maturity for agronomic and aflatoxin evaluation of each hybrid into barcoded bags. Quantification of aflatoxin was conducted with monoclonal antibody affinity columns and fluorescence determination (Vicam AflatestTM). Seven experimental Texas A&M University (TAMU) entries were included in a Southern East Regional Aflatoxin Test (SERAT) trial of 31 hybrids and checks planted at eight locations including College Station, Ganado and Halfway, TX; Tifton, GA; Alexandria, LA; Mississippi State, MS; Lewiston, NC; and South Carolina, for yield and/or aflatoxin evaluation. Cooperators included several entries in order to obtain better analyses of the environmental interactions among their best germplasm. Three of these hybrids accumulated less aflatoxin than the mean of the test at College Station 786 parts per billion (ppb), with three accumulating less than 200 ppb. In addition, a smaller aflatoxin only cooperative trial was also planted. For breeding material, in the summer College Station, TX, nursery and the winter Weslaco, TX, nursery a total of 210 Texas AgriLife lines proven in past yield trials were crossed to any of 14 new elite commercial and three ex-Plant Variety Protection testers. We created sufficient seed from 446 new unique hybrids between different TAMU elite lines to test in the next growing season. There should be many outstanding hybrids identified from this objective. This objective is foundational to the success of getting TAMU germplasm into commercial hybrids, and thus grower’s fields as quickly as possible. Additionally over 1,000 other plots were planted for advancement, increase and testcrosses for future testing. This coming year we plan to continue collaboration with SERAT, a USDA aflatoxin study, and with many different collaborators for hybrid yield trials. In addition we will continue our own breeding activities for high yielding aflatoxin resistant material.