|Willcox, Martha - MISSISSIPPI STATE UNIV|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 1, 2004
Publication Date: January 1, 2005
Citation: Brooks, T.D., Williams, W.P., Windham, G.L., Willcox, M.C., Abbas, H.K. 2005. Quantitative trait loci contributing resistance to aflatoxin accumulation in the maize inbred Mp313E. Crop Science. 45:171-174. Interpretive Summary: Aflatoxin is a toxic compound produced by the fungus Aspergillus flavus and is a problem to mid-south corn producers. High levels of aflatoxin can build up in corn kernels while in the field thereby reducing its value and usefulness. Corn lines that tend to reduce the build up of aflatoxin have been identified. These lines, however, lack certain characteristics that seed companies and producers desire such as early maturity and high yield. Attempts to transfer the resistance to more favorable corn lines have been hindered by environmental interactions and related undesirable traits. As a result, all of the most common corn hybrids sold are highly susceptible to aflatoxin accumulation. This study was designed to utilize molecular techniques to help identify specific regions of the ten corn chromosomes associated with aflatoxin accumulation resistance and to aid in transfer of those regions to a more favorable corn line. Mp313E, a resistant corn line, and B73, a susceptible corn line, were used in our studies. Field tests were conducted at two locations over three years to study environmental effects on resistance. Five different chromosomal regions were identified in Mp313E that contributed to lower levels of aflatoxin accumulation. Only two of these regions, one on chromosome two and one on chromosome four, decreased aflatoxin accumulation in at least three environments. The region on chromosome two reduced aflatoxin accumulation from 7% to 18%, depending on environment, while the region on chromosome four reduced aflatoxin accumulation from 8% to 16% when present in the plant. These two regions contribute to significant reductions in susceptibility to aflatoxin accumulation and are being transferred to B73. Resulting corn lines should have the resistance from Mp313E while still retaining the agronomic characteristics of B73 and be useful to seed company breeding programs.
Technical Abstract: Aflatoxin is a carcinogenic and toxic compound produced by the fungus Aspergillus flavus that can be found at detrimentally high concentrations in maize grain. Screening has led to the discovery of sources of resistance to aflatoxin accumulation in maize, but poorly associated agronomic characteristics and complex inheritance have limited transfer of resistance to elite inbreds. A set of 210 F2:3 families derived from a cross between the resistant inbred Mp313E and the susceptible inbred B73 were evaluated in replicated trials in four environments for resistance to aflatoxin accumulation. Families were also genotyped using SSR markers to develop a genetic map for quantitative trait loci (QTL) analysis. Composite interval mapping was used to identify 2, 3, 5, and 3 QTL within the tests at Stoneville (2000) and Mississippi State (2000, 2001, 2002) respectively. QTL were primarily additive in nature with the Mp313E parent contributing to reduced aflatoxin concentration in all but one case. Two QTL regions were significant in at least three environments. Afl3, represented by marker bnlg371, was located on chromosome two and accounted for 7% to 18% of variation in aflatoxin levels depending on environment. Afl5, represented by marker bnlg2291, was located on chromosome four with explained variance ranging from 8% to 16%. This QTL has been noted in earlier studies while afl3 is new. Identified QTL confirm important regions influencing aflatoxin accumulation previously identified and present new ones of equal effect.