Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 10/3/2003
Publication Date: 10/3/2003
Citation: Xu, W., Odvody, G., Williams, W.P. 2003. Progress toward developing stress-tolerant and low-aflatoxin corn hybrids for the southern states [abstract]. 16th Annual Aflatoxin Elimination Workshop Proceedings. p. 63.
Technical Abstract: Aflatoxin contamination of corn, caused by A. flavus, is a chronic problem in Texas and the southern United States. A hot and dry environment and corn earworm (Heliocoverpa zea) feeding increases the aflatoxin level. Drought and heat tolerant corn have less grain molds under drought stress. We believe that genetic improvement of drought tolerance, heat tolerance, and corn earworm resistance can reduce the aflatoxin risk in Southern environments. Experimental hybrids and commercial checks were grown at Corpus Christi and the High Plans in Texas. Aflatoxin was measured only at Corpus Christi. The Corpus Christi tests were planted late (early April) to encourage severe drought stress at later stages of maturity. The tests used a randomized complete block design with nine replications. When the first hybrid was at mid silk, corn kernels colonized by a high aflatoxin-producing isolate of A. flavus (NRRL3357) were distributed between all rows at 1 kg dry seed equivalent per 9.4 m. This provided the increased and uniform aerial dissemination of conidia, which favored greater infection by the high aflatoxin producing isolate but without any physical injury to ears and kernels. Ears from each plot were hand-harvested. All ears were threshed and agronomic data were recorded including grain yield. To reduce aflatoxin assay costs, grain from the original replications were systematically pooled to three composite replications and analyzed for aflatoxin content. Replications 1, 2, 3 were pooled to form composite rep 1, and reps 4-6 and 7-9 to form composite reps 2 and 3. All grain from each composite replicate was 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 differences among hybrids. Natural log transformation of aflatoxin data was made before data analysis. The average aflatoxin level was 398 ppb, 1276 ppb, and 849 ppb for the tests in 2000 (20 hybrids), 2001 (14 hybrids), and 2002 (12 hybrids), respectively. In the three years, our hybrid Tx202 x CML343 consistently had low aflatoxin contamination (120 - 207 ppb) which was 69% to 92% lower than the check Pioneer hybrid P31B13. In 2003, the aflatoxin at Corpus Christi ranged from 31 to 240 ppb with a mean of 97 ppb. Four experimental hybrids had significantly lower aflatoxin (31 to 54 ppb) than the check 31B13 (161 ppb). The experimental hybrids were developed by the corn-breeding program of the Texas Agricultural Experiment Station (TAES) in Lubbock. The low-aflatoxin TAES hybrids yielded equally or significantly higher in comparison to the checks at Corpus Christi and in the High Plains. For example, S1W x CML343 yielded 14,288 kg/ha while 31B13 produced 13,946 kg/ha under irrigated conditions at Halfway, TX. The TAES experimental hybrids and their parental lines were selected for drought and heat tolerance, CEW resistance and overall agronomic performance. They have tight husk, good ear tip coverage, significantly lower grain mold and less ear injuries by corn earworm. Results indicate that breeding for drought tolerance and earworm resistance is a promising approach to reduce aflatoxin contamination in corn grown in Southern environments.