Identifying quantitative trait loci (QTLs) for fumonisin accumulation and ear rot resistance in maize (Zea mays L.)

Fusarium verticillioides and F. proliferatum are fungal pathogens of maize that cause ear rot and contaminate maize with fumonisin. The first objective was to investigate the relationship between Fusarium ear rot and fumonisin contamination. Two populations, BC 1F1:2 families created from the cross of GE440 x FR1064 (GEFR population) and recombinant inbred lines created from the cross of NC300 x B104 (NCB population) were studied. Moderate to high heritabilities and strong genetic correlations between ear rot and fumonisin concentration were estimated and suggest that selection for reduced ear rot should frequently identify low fumonisin lines. Quantitative trait loci (QTL) mapping was then used to study genetic relationships between the two traits and to investigate consistency of QTL across populations. Eight QTL in the GEFR population and five QTLs in the NCB population affected both traits. At least three ear rot and two fumonisin contamination QTLs mapped to similar positions in the two populations. Two QTL appeared to be consistent for both traits across both populations. To investigate the relationship between resistance and agronomic utility in the GEFR population, yield and agronomic performance were measured in line testcrosses. Correlation and QTL analyses were employed to study these relationships. QTLs identified included 7 yield, 5 grain moisture, 8 plant height, 6 ear height, 3 silk date, and 4 tassel date QTLs. If backcrossing were utilized to move fumonisin contamination resistance alleles into the FR1064 background, our correlation results suggest that correlated responses would include an increase in grain moisture and a decrease in stalk lodging. Our QTL mapping results suggest that only a small reduction in grain yield and a small increase in plant height would be expected from backcrossing fumonisin resistance alleles into FR1064. However, marker-assisted selection may facilitate breaking linkages between resistance alleles and alleles reducing agronomic performance. The second objective was to investigate the resistances to Fusarium and Aspergillus ear rots and fumonisin and aflatoxin contamination in selected lines. Based on the NCB study, the 24 highest and 24 lowest mean fumonisin concentration lines were selected. The low fumonisin group had significantly lower levels of both mycotoxins and ear rots. All four traits were significantly correlated, suggesting that at least some of the genes involved in resistance to ear rots and mycotoxin contamination by these fungal species are identical or genetically linked.