Quantitative trait loci for resistance to Stenocarpella maydis and Fusarium graminearum cob rots in tropical maize

Stenocarpella maydis and Fusarium graminearum are the predominant species causing maize (Zea mays L.) cob rots in the tropics and sub-Saharan Africa. Developing varieties resistant to cob rots is an alternative strategy that is practical and provides better insurance for small-scale farmers. The subjectivity of scoring and the varying virulence responses of these pathogens to environmental conditions make selection for resistance difficult. The objectives of this study were to map quantitative trait loci (QTL) associated with resistance to S. maydis and F. graminearum and to analyze the possibilities of utilizing these QTL for marker-assisted selection (MAS). Stable QTL mapped were Fg_4,2 (r2 = 0.22) and Sm_4,1 (r2 = 0.16) associated with resistance to F. graminearum and S. maydis, respectively, on chromosome 4. Another QTL associated with resistance to F. graminearum was Fg_5 (r2 = 0.30) on chromosome 5. A QTL with pleiotropic effect was detected on chromosome 1, 22 cM from umc1269 marker (r2 values of 13% and 22% for resistance to S. maydis and F. graminearum, respectively). Additive effects ranged from -0.14 to -0.35 for associated QTL of both pathogens, and all mapped QTL were more than 5 cM from the nearest molecular marker utilized in the study. Therefore, there is need to utilize the maize genomic map to identify and test several markers, < 5 cM, near the detected QTL, in order to locate more reliable molecular markers for utilization in MAS.