Abstract

Sporisorium ehrenbergii Vánky is the causal agent of long smut (LS) on sorghum in several African and Asian countries. For effective breeding programs to evolve LS resistant varieties to control this important disease, information on the current status of physiological races of S. ehrenbergii is most essential. In this study, when teliospores of 22 collected isolates were cultured on PDA medium at 30°C for 15 days, three distinct and frequent morphological colonies were observed and they were designated as form No. 1, 2, and 3. Virulence of these isolates and their forms was tested on certain sorghum genotypes/varieties which could serve as a set of differentials for evaluating resistance to LS in field experiments to characterize the putative virulent races. All 7 isolates of the form No. 2 were highly virulent (HV) on all 13 tested sorghum genotypes/varieties, and they were designated race No. 2. In contrast, all 6 isolates of the form No. 1 were only HV on 3 tested sorghum genotypes/varieties (race No. 1) and all 9 isolates of the form No. 3 were HV on 9 tested sorghum genotypes/varieties (race No. 3). Following in vitro screening test, water extracts of rheum (Rheum rhabarbarum) and common walnut (Juglans regia) at 1% exhibited full inhibition of teliospore germination of S. ehrenbergii. Moreover, spraying inoculated sorghum plants with 1% rheum and common walnut extracts twice during panicle emergence significantly reduced the incidence of LS compared with untreated control plants.

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