| Gray leaf spot (GLS) caused by Cercospora zeae-maydis (Tehon and Daniels) and southern corn leaf blight (SCLB) caused by Bipolaris maydis (Nisik.) are fungal diseases of maize (Zea mays L.).; In 1985 and 1986, over 1,000 experimental and public maize lines were screened for GLS resistance. From these lines, eight different maize lines were chosen which had high levels of GLS resistance and which had 0% to 100% tropical germplasm. These lines were used as the basis for conducting four different studies: (1) identification of quantitative trait loci (QTLs) controlling resistance to GLS, (2) identification of QTLs controlling resistance to SCLB, (3) diallel analysis of resistance to GLS, and (4) restriction fragment length polymorphism (RFLP) based genetic distance.; The primary objective of the first two studies was to identify QTLs for GLS and SCLB resistance in three single-cross populations of maize using RFLPs as molecular markers. In addition, we attempted to determine the consistency of QTLs over environments and populations, and type of gene action closely linked to individual marker loci. Based on single-factor ANOVA, detectible individual markers accounted for 2% to 27% of the phenotypic variation. QTLs for both traits were variable over environments and over populations. Additive gene action was the predominant type of gene action displayed for GLS and SCLB resistance.; The objective of the third study was to evaluate general and specific combining ability and reciprocal effects in a diallel design which included nine parents, F{dollar}sb1{dollar}s, F{dollar}sb2{dollar}s, and most reciprocals. The parent, GCA, and SCA effects were highly significant in both the F{dollar}sb1{dollar} and the F{dollar}sb2{dollar} analyses.; The primary objective of the fourth study was to determine the genetic relatedness of 13 very diverse maize lines based on 229 RFLP probe-enzyme combinations. In addition, correlations between RFLP-based genetic distances (GDs), GLS ratings, and grain yield were calculated. GDs based on all 229 probe-enzyme combinations ranged from 0.49 to 0.82, with an average GD of 0.70 over all possible pairs. |
