Resistance To Aflatoxin Accumulation In Maize

Abstract

Aflatoxins are carcinogenic compounds produced by the fungal pathogen Aspergillus flavus and other Aspergillus spp. A. flavus infects maize (Zea mays L.) and other agricultural commodities. Regulation in developed countries permits only extremely low levels of aflatoxin in food, and as a result farmers are exposed to significant economic losses. In developing countries, where A. flavus populations are more prevalent and regulations are rarely enforced, aflatoxins cause significant health burdens for human populations. Management with the use of maize lines that are resistant to aflatoxin accumulation could benefit farmers around the world. Little is known about the factors contributing to resistance and its interaction with the environment. The objective of this dissertation was to better understand resistance to aflatoxin accumulation in maize so that this resistance can be incorporated into maize hybrids. A new technique for the evaluation of A. flavus colonization using quantitative real-time PCR (qPCR) was developed and validated. There was a strong correlation between colonization of A. flavus, as measured by qPCR, and aflatoxin levels. In addition to resistance to aflatoxin accumulation, variation was detected in maize for susceptibility to silk and kernel colonization. Resistance to aflatoxin accumulation was correlated with flowering time, and with kernel physical traits, such as fiber, ash, carbohydrate and seed weight. An analysis of the inheritance of resistance was conducted in the CML322 x B73 population. Moderate levels of heritability (63%) suggested that significant gains could be obtained from breeding with this population. Thirteen quantitative trait loci (QTL) for resistance to aflatoxin accumulation and other silk and kernel traits were found in three years of experiments. iii One QTL with moderate effect in maize bin 4.08 was confirmed using near isogenic lines. A meta-analysis of QTL was conducted with all the reported QTL found in the literature including QTL for resistance to other ear rots. This meta-analysis indicated that QTL for multiple ear rot diseases co-localize. The analysis resulted in reduced confidence intervals, presumably increasing the feasibility of breeding strategies that utilize molecular markers. iv