Improving Resistance to Fusarium Ear Rot and Fumonisin Contamination and Increasing Yield with Exotic Maize Germplasm.

Abstract

Exotic and unadapted varieties contribute advantageous alleles to crop species. Incorporating exotic germplasm into adapted lines has the additional advantage of broadening the genetic diversity within the common maize germplasm pool. I explore contributions of unadapted or exotic maize germplasm to improved resistance to Fusarium ear rot and fumonisin accumulation or topcross grain yield (quantitatively inherited traits) using different breeding approaches and population structures. Topcrosses of BC1F1:2 lines, developed by backcrossing GE440 FR1064 and selected for divergent levels of resistance to Fusarium ear rot and fumonisin contamination, were used to test the hypothesis that inbred lines with greater resistance to fumonisin contamination produce hybrids with greater ear rot resistance and greater resistance to yield loss under inoculation. Experimental results did not support the hypothesis, but this result may have been due to low levels of infection in the field trials. Selected BC4F1:3-derived lines representing advanced backcross generations of GE440 alleles into the FR1064 genetic background and their topcrossed hybrids were evaluated in field trials for disease resistance and yield potential. Experimental results demonstrate that advanced backcross generations produce lines comparable to FR1064 for grain yield but with better ear rot and fumonisin resistance, that indirect selection for reduced fumonisin content by selection for ear rot resistance was partially effective, but that selection for improved inbred disease resistance again did not result in improved topcross disease resistance. A random-mated, genetically broad-based population referred to as the Resistant to Fusarium population, was developed to combine alleles for Fusarium ear rot resistance and improved agronomic traits from diverse maize germplasm. One cycle of selection was conducted in this population to test the hypothesis that index selection for reduced Fusarium ear rot, reduced lodging, and increased yield results in reduced fumonisin contamination. Selected lines were not significantly different than the base population for ear rot percentage or fumonisin content. In topcrosses, however, selected lines showed significant improvement for ear rot resistance and fumonisin accumulation compared to the unselected Cycle 0 topcross control. Additional cycles are needed to increase favorable allele frequencies for each of the target traits. By genotyping a segregating F2:3 population from a cross between phenotypically distinct F4-derived sister lines I identified the genome region(s) conferring a topcross yield difference in a nearly-isogenic genetic background and determined that the tropical parent was the source of the favorable allele(s).