Combining ability for resistance to field aflatoxin accumulation in maize grain

In this study general (GCA) and specific combining abilities (SCA) for resistance to preharvest aflatoxin accumulation in grain of maize was determined, utilizing A619 Lfy syn, A632 Lfy syn, B73 Lfy syn, Hy Lfy syn, Mo17 Lfy syn, Wf9 Lfy syn, and 914 Lfy syn. 21 F1 crosses from a diallel were evaluated for aflatoxin accumulation in grain in three environments. 21 days after mid- silk, ears were slash-inoculated with Aspergillus parasiticus. Samples were analyzed for aflatoxins B1, B2, G1, and G2. Significant differences for aflatoxin accumulation were detected among environments, with the drought stress environment showing the highest concentration for all four aflatoxins. The GCA and crosses mean squares were not significant for any aflatoxin and the SCA mean square was significant only for aflatoxin G2. Relatively small quantities of aflatoxin accumulation on, and nonsignificant differences among the 21 F1 crosses might be indicative of their inherently high resistance levels. The SCA sums of squares constituted 2/3 or more of crosses sums of squares, which indicated preponderance of dominance and/or epistatic effects for aflatoxin accumulation. The Hy Lfy syn GCA effect tended to increase B1, and Wf9 Lfy syn tended to reduce G1 accumulation. For B2, a significant environments (E) x crosses (C) interaction was largely due to E x GCA interaction, which was due to an interaction of the B73 Lfy syn GCA effect with E. This interaction effect tended to reduce B2. The E x C interaction for G2 was due to both E x GCA and E x SCA interactions. B73 Lfy syn GCA x E tended to reduce G2 and Mo17 Lfy syn GCA x E tended to increase G2. Additive genetic correlations based on GCA effects among the four aflatoxins were significant, except the correlation between aflatoxins B1 and G2, suggesting that, in general, increasing resistance to one toxin may lead to resistance to the other three toxins.