Combining Ability Analysis of Recombinant Inbred Lines Developed from YML32 × Q11 Cross for Grain Yield and Resistance to Gray Leaf Spot.

Developing resistant lines and hybrids is an economical way to control diseases for improving yield stability and grain yield in maize (Zea mays L.). The objectives of this study were to 1) investigate if differences with respect to grain yield (GY) and resistance to gray leaf spot scores (GLS) caused by Cercospora zeina existed among recombinant inbred lines (RILs) with and without the GZ204/IDP5 DNA segment that offers resistance to GLS (RDNAS); and 2) evaluate general combining ability (GCA) and specific combining ability (SCA) effects expressed in distinct genetic backgrounds. Four RILs (three containing RDNAS) were developed via marker-assisted selection (MAS) from a cross between a line carrying the RDNAS and an elite line susceptible to GLS (Q11). The four RILs and the susceptible parent (Q11) were used as testers to cross with 13 maize lines of known heterotic groups. The three RILs with the RDNAS showed reduced gray leaf spot scores (GLSS) and small GCA effects for GLSS, but they did not differ in GY. RL2_1 was the best RIL for improving GLS resistance. All RILs with the RDNAS did not have the same level of resistance to GLS. The RILs with the RDNAS had lower GLSS in crosses with lines from the Suwan1 heterotic group than those from Reid and non-Reid heterotic groups, suggesting additional resistance genes or quantitative trait loci (QTL) besides the RDNAS may be present in Suwan1. Thus, use of lines related to Suwan1 could be highly effective in enhancing resistance to GLS.