Genetics and Associations of Carotenoid Concentrations and Aspergillus flavus Resistance in Maize (Zea mays)

Aflatoxin is a toxin produced by the fungus Aspergillus flavus, which infects and contaminates seed crops including maize. Aflatoxin contamination in maize grain causes economic losses and health hazards. Inhibition of fungal growth and aflatoxin biosynthesis by provitamin A (proVA) carotenoids at concentrations greater than currently found in maize have been reported from in vitro studies. Characterization of resistance to Aspergillus ear rot and aflatoxin accumulation is inconclusive, and estimations of gene action are needed. Therefore, diallel analysis was carried out for 36 F1 hybrids obtained by crossing 9 maize inbred lines from CIMMYT using Griffing's method 4. Hybrids were planted in four environments with four replications in Mexico (i. e. Agua Fria and Tlaltizapan) during 2012 and 2013, and one environment with three replications in Mississippi, USA during 2012. The primary ear of each plant was inoculated with A. flavus 14-17 days after silking and percent ear rot (pER), percent bright greenish yellow fluorescence (pFL) and aflatoxin concentration (AFT) were evaluated at or shortly after harvest. Combining ability analyses indicated greater importance of additive relative to non-additive gene effects for all three traits. A second experiment studied the association of carotenoids with Aspergillus ear rot and aflatoxin accumulation in grain. One hundred twenty F1 hybrids obtained from a North Carolina Design II mating of 20 CIMMYT orange or yellow lines (10 high and 10 low for proVA) with 6 white inbred lines (resistant or susceptible to Aspergillus ear rot and aflatoxin accumulation) were evaluated for pER, pFL and AFT in the same environments as for the diallel experiment. ProVA, beta-carotene, beta-cryptoxanthin and zeaxanthin showed significant negative correlations (r = -0.23 to -0.35, P<0.01) with aflatoxin concentrations in grain. Reciprocal effects were not significant for A. flavus-related traits, pER, pFL and AFT. Three yellow lines with high carotenoid concentrations had favorable GCA effects for aflatoxin and Aspergillus ear rot, and are potentially valuable lines for use in breeding efforts to simultaneously address proVA biofortification and reduction of aflatoxin concentration in grain.