Submitted to: Cereal Research Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/1999
Publication Date: N/A
Interpretive Summary: Stem and root diseases caused by the fungus Macrophomina phaseolina are serious and can reduce yields in many crops including bean, sorghum, cotton and over 400 other crop species. In sorghum, the disease is most common in regions where high temperatures and drought stress are encounter- ed during the end of the growing season. The best method for controlling the disease is the use of resistant varieties, since other approaches, suc as the use of chemical fungicides or supplemental irrigation are generally not economically viable alternatives for commercial sorghum production. The work reported here concerned an analysis of the genetic basis of resistance in sorghum to the fungus. Nine elite sorghum breeding lines were crossed in all possible combinations (36) and the nine parents and 36 hybrid families were evaluated in two different field locations in Mexico for two years. Differences were observed between parents and between hybrids for resistance levels. In both locations for both years, the hybrids were never significantly more resistant than their parents. These results indicated that it is possible to breed for enhanced resis- tance to the fungus, but that it is not necessary to make hybrids. This is of significant interest to governmental agencies and private companies involved in the production of sorghum seed, since producing hybrids requires the control of pollination, and this is a very laborious and costly process. These results will assist in reducing costs associated with the development of resistant varieties.
Technical Abstract: Charcoal rot of sorghum, caused by the fungus Macrophomina phaseolina, is a severe disease in regions where sorghum encounters post-anthesis drought stress. Previous reports disagree with respect to the nature of the genetic factors that condition resistance to charcoal rot. A diallel cross was made using nine genetically diverse sorghum lines. Parental lines and F1 progenies were evaluated in the field in 1997 and 1998 at two locations. Lines were significantly more resistant than F1s, indicating that heterosis was not affecting resistance. General combining ability (GCA) and specific combining ability (SCA) effects were significant for both locations over both years. However, the magnitudes of SCA effects were much smaller than GCA effects. These observations indicate that resistance to charcoal rot is conditioned by both additive and non-additive effects.