A quantitative genetic study on the inheritance of the resistance to head smut (Sporisorium reilianum (Kuhn) Langdon and Fullerton) in maize (Zea mays L.)

Abstract

Two groups of susceptible and resistant inbred lines of maize, their crosses, and other derived generations within each group were evaluated under field and greenhouse for resistance to head smut caused by Sporisorium reilianum (KOhn) Langdon and Fullerton. The experiments were conducted to determine i) the type of gene action involved in the resistance, ii) the inheritance and heritability of the resistance, iii) the genetic components among various agronomic traits most influenced by the effect of the disease, iv) the efficiency of the traditional diallel analysis vs. the generation means analysis of Gardner and Eberhart and v) the stability of the resistance to head smut in maize over time based on the genetic control. The three genetic analyses coincided to determine that additive gene effects had a greater contribution to the resistance to head smut. Additive effects accounted for the majority of the variation but dominant and epistatic effects were also significant. According to the generation means analysis, additive effects accounted for 73% and 43%, heterotic effects 10% and 20 for the Texas and Corn Belt groups respectively. Additionally, the model accounted for the contribution of epistatic effects of the additive and dominant type. Broad sense heritability estimated on F. families was low for the field evaluation, contrasted with a H2 = 73% for the greenhouse evaluation. It was found that the disease has a greater impact on the heterotic component of the variation. This observation was consistent over genetic analysis and over agronomic traits evaluated. The stability that head smut has displayed over time and over geographical distribution can be attributed to combinations of several genes contributing to the resistance in an additive mode. Also contributions from dominant genes acting independently or jointly, depending on the hybrid combination. This represents a genetic combination that the pathogen is less likely to overcome as compared with the sorghum model where single dominant genes have allowed pathogen variation to overcome the resistance mechanism. The level of resistance in inbred lines have not changed over time and probably will not support a major shift to pathogenicity by S. reilianum.