Analysis of stalk rot resistance and genetic diversity among drought tolerant sorghum genotypes

Forty-five drought tolerant sorghum [Sorghum bicolor (L.) Moench] genotypes were screened for stalk rot resistance by artificial inoculation with Fusarium proliferatum in field trials near Manhattan, KS, in 2000. Four lines, SC134, SC1154, SC1039, and SC564, were identified with lesions that were smaller than the standard resistant check, SC599. These lines and four other checks were intercrossed in a Design II mating scheme with 'A Wheatland' and 'A Redlan' to produce hybrids for further testing. The inbred parent lines and corresponding hybrids were evaluated for resistance to four major stalk rot pathogens, F. proliferatum, F. thapsinum, F. andiyazi, and Macrophomina phaseolina, using randomized complete block designs in field trials near Manhattan and Hesston, KS, in 2001. Significant differences in lesion length were detected among the inbred parent lines and their corresponding hybrids. Comparisons among entries indicated that crosses of SC701 and SC564 were susceptible and produced very large lesions following inoculation with each of the stalk rot pathogens evaluated in this study. Only small lesions were produced in SC599 and its hybrids following inoculation with either Fusarium species or M. phaseolina. SC134 also exhibited high levels of resistance to Fusarium species and SC35 to M. phaseolina. Comparisons among pathogens showed that inoculations with M. phaseolina produced larger lesions than the Fusarium species in most sorghum genotypes. The most resistant accessions in these studies were all from East Africa; therefore, an analysis of genetic diversity was conducted to evaluate the pattern of genetic relationships among the full set of drought tolerant lines. DNA fingerprinting followed by cluster analyses grouped the entries into five distinct clusters, mainly according to geographical origin. Three, of the resistant lines grouped together in a cluster that contained mostly Ethiopian landraces while SC599 grouped in another cluster.