Date of Award

1991

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Plant, Environmental Management and Soil Sciences

First Advisor

Manjit S. Kang

Abstract

Preharvest infection of maize (Zea mays L.) grain by Aspergillus flavus Link ex Fries and subsequent aflatoxin contamination is a serious problem, especially in the southeastern USA. Studies on the genetics of resistance to aflatoxin contamination in maize are quite limited, but a better understanding of this aspect is needed for developing resistant germplasm. The objective of the first field study was to determine the genetics of resistance to aflatoxin contamination in maize possessing the leafy (Lfy) gene. Seven Lfy synthetic genotypes were crossed in a diallel fashion, and the resulting 21 single crosses were evaluated for aflatoxin contamination in three Louisiana environments. Twenty-one days after mid-silk, ears were slash-inoculated with A. parasiticus Speare. Aflatoxin contamination differed significantly among the three environments. General combining ability mean squares were slightly greater than specific combining ability mean squares for aflatoxins B$\sb1$, B$\sb2$, G$\sb1$, and G$\sb2$. Crosses involving genotypes Wf9 and B73 had the lowest aflatoxin concentrations, indicating that these genotypes may have some resistance to aflatoxin contamination. High additive genetic correlations suggested that increasing genetic resistance to one toxin should lead to cross resistance to the other three toxins. A second field study was undertaken to determine the difference in aflatoxin production by A. flavus and A. parasiticus via silk inoculation. Seven maize synthetics containing the Lfy gene, grown in three environments, were inoculated twice, i.e., 14 and 21 days after mid-silk, by atomizing over silks a 2 ml suspension of conidia containing 20 $\times$ 10$\sp6$ spores ml$\sp{-1}$ of either A. flavus or A. parasiticus. Aflatoxin contamination of maize by A. flavus occurred in all three environments, but contamination by A. parasiticus was detected in samples from only one environment where moisture stress occurred. Aspergillus flavus produced significantly higher levels of aflatoxin B$\sb1$ and B$\sb2$ than did A. parasiticus, suggesting that A. flavus was a more aggressive invader of maize kernels via silks. Differentiation among genotypes for aflatoxin contamination was not possible with the silk inoculation.

Pages

83

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