VIEW ARTICLE

Resistance

Inheritance of Resistance to Tar Spot Complex in Maize. H. Ceballos, Maize Program, Centro Internacional de Mejoramiento de Maíz y Trigo (CIMMYT), Apdo. Postal 6-641, Mexico, D.F. 06600, Present address: c/o CIAT, Apdo. Aéreo 6713, Cali, Colombia; J. A. Deutsch, Maize Program, Centro Internacional de Mejoramiento de Maíz y Trigo (CIMMYT), Apdo. Postal 6-641, Mexico, D.F. 06600. Phytopathology 82:505-512. Accepted for publication 13 November 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-505.

Tar spot complex (TSC) of maize can cause serious yield losses in Latin American countries. Phyllachora maydis is the most important pathogen associated with TSC. Little is known about the genetics of resistance to this disease. This study was carried out to elucidate the inheritance of resistance to P. maydis found in S₂ lines from a CIMMYT (International Maize and Wheat Improvement Center) maize population. Segregation and diallel analyses were performed in three environments. In the segregation analysis, each of three resistant lines (P_R) was crossed with a susceptible one (P_s) and the following generations obtained: F₁, F₂, F₃, and the backcrosses of F₁ to P_R and P_S. Expected segregation ratios for resistance and susceptibility, based on hypothetical genetic models, were compared with experimental data through a chi-square test. A joint-scaling test also was performed on one set. Results indicated the presence of a single dominant gene controlling the resistance in at least two of the three parental lines evaluated. The diallel analysis evaluated the reaction to P. maydis in eight parental lines. Significant general and specific combining ability effects (P< 0.01) were associated with resistance. This is the first published study on the genetics of resistance to TSC.