Location: Corn Host Plant Resistance Research2010 Annual Report
1a. Objectives (from AD-416)
The objectives of this proposal are: (1) to evaluate aflatoxin, yield, and agronomic traits of the new high yielding TAES experimental hybrids for a second year; (2) to conduct large scale strip tests of S2B73BC x BC300 and S1W x CML343 for yield, aflatoxin level, and agronomic traits in TX; (3) to develop and advance new lines toward producing low-aflatoxin corn hybrids; and (4) to participate in SERAT tests. The results from this research will help the seed industry to commercialize the new germplasm and lead to the release of new inbred lines and hybrids with multiple stress tolerance and adaptation to Texas and southern states.
1b. Approach (from AD-416)
Corn hybrids developed by Texas Agricultural Experiment Station and other widely grown hybrids will be grown at locations in Texas and Mississippi under different degrees of drought stress. At some locations the hybrids will be inoculated with Aspergillus flavus. Data will be recorded on flowering date, plant height, lodging, and other agronomic traits. Mature ears will be hand harvested and rated for ear mold and insect damage. Grain will be analyzed for aflatoxin contamination. The proposed research will help to identify multiple stress resistant corn and provide the germplasm and information needed by the seed industry to develop and commercialize hybrids with resistance to aflatoxin contamination.
3. Progress Report
Contamination of corn grain with aflatoxin, which is produced by the fungus Aspergillus (A.) flavus, is a chronic problem in the southern United States. Hot, dry environments stress corn plants and increase the accumulation of aflatoxin. Producers need corn hybrids with resistance to aflatoxin contamination. Our strategy for breeding corn with resistance to aflatoxin contamination is to improve drought and heat tolerance, increase resistance to corn earworm damage, and stack genes from known sources of resistance such as Mp715 developed and released by ARS at Mississippi State (6406-21000-011-00D) into germplasm adapted to the southern states. Experimental hybrids were developed, 28 from a breeding cross containing Mp715, and evaluated in a randomized complete block design with three replications. The Lubbock and Halfway, TX, locations had optimum and limited irrigation treatments. Plants in Lubbock, TX, and Starkville, MS, were inoculated one week after silking by injecting 3-ml conidia solution of Aspergillus flavus NRRL3357 (1.5 x 106 conidia/ml) into silk channels. Ears from each plot were hand-harvested, rated for corn earworm feeding damages and ear traits, and then threshed for grain yield. Grains were initially ground in a Romer mill at the coarse grind setting. After thoroughly mixing the ground kernels, a 200 g sub-sample was ground again at the finest grind setting on the mill. Aflatoxin B1 assay was done on 50 g sub-samples of the finely ground material for each composite replication using the Vicam immunoassay/fluorometer system. Standard ANOVA was performed to test the difference among hybrids. Natural log transformation of aflatoxin data was made before data analysis. The aflatoxin was significantly different among the hybrids. A susceptible check hybrid exhibited high aflatoxin (416 ppb). Commercial hybrid checks were also susceptible with 1155 and 456 ppb. All crosses of Mp715-derived lines with C2A554-4 generally had low aflatoxin as compared to the crosses with Tx205 and a proprietary line with Bt gene. C2A554-4 is a drought tolerant line. This result indicates that stacking aflatoxin resistant QTLs with drought tolerance can effectively reduce aflatoxin accumulation. The low-aflatoxin hybrids also produced grain yields comparable to the commercial checks across test locations. We are preparing to release these new aflatoxin resistant inbred lines. An association mapping panel consisting of the single-cross testcrosses from 300 diverse corn inbred lines was planted in Lubbock, TX, April 10, 2009, in a randomized complete block design with three replications. The plants were well watered in the entire season with a sub-surface drip irrigation. Detailed data were collected on plants per plot, plant and ear height, pollen shed and silking date, husk coverage, ear length, corn earworm feeding damage, percentage of molded kernels, and grain weight of 10 harvested ears. Activities were monitored through a meeting of cooperating scientists, administrators, producers, and scientists from commercial companies held at Mississippi State, conference calls, e-mails, written reports, and phone calls.