The nature of resistance to head smut Sphacelotheca reiliana (Kuhn) Clint in Sorghum bicolor Moench (L.)

Abstract

Seven sorghum inbred lines and 42 F1 hybrids from a set of diallel crosses among the lines were evaluated for reaction to head smut Sphacelotheca reiliana (Kuhn) Clint. Known vertical genes stacked into a single genotype to confer horizontal (general) resistance against the pathogen were also evaluated. The parental lines were first tested for reaction to six populations of head smut collected at Berclair, Corpus Christi, Gregory, Victoria, Halfway and Kress, Texas. The populations represented prevalent genotypes of the smut pathogen. Twenty 4-week old seedlings of each inbred were artificially inoculated in the greenhouse by a hypodermic technique and percentage of smut infection calculated. Differential reactions were observed for all populations. Three sources of resistance and four for susceptibility were identified for Berclair, Gregory and Victoria populations, whereas four sources of resistance and three for susceptibility were identified for Kress, Halfway and Corpus Christi populations. 'Spur Feterita' and 'White Kafir' were the only inbreds showing a high level of resistance, since they were immune to all populations. 'Standard White Milo' was susceptible to the Berclair and Gregory isolates, and resistant to all others. 'RTAM 428' exhibited resistance to all populations except the one from Victoria. The lines were crossed in all combinations to determine type of gene action involved in expression of resistance to head smut. Data were collected from progenies and parents inoculated with the Berclair population. In testing for horizontal resistance the Kress population represented the smut pathogen source. Analysis of variance of the diallel table using only six parents revealed significant additive and dominance effects and non-reciprocal differences. The slope of the regression line in the Wr - Vr graph was not significantly different from unity, indicating dominance and no complication of gene interaction. Lack of significance of the Wr - Vr analysis indicated that the assumptions of the biometrical model were valid...