Elicitation of defense response genes in sorghum floral tissues infected by Fusarium thapsinum and Curvularia lunata at anthesis
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Grain mold of Sorghum bicolor is one of the leading constraints for the production of optimum quality sorghum grain worldwide. Differences in mold levels among different varieties grown in the same environment imply that genes play a role in controlling mold severity. In order to determine if genes that function in active defense responses also affect molding, panicles of resistant and susceptible cultivars were inoculated at anthesis with conidial suspensions of Fusarium thapsinum and Curvularia lunata, the fungi most often found in naturally infected grain. RNA was extracted from the immature floral tissues at various times following inoculation. Levels of mRNA for four known defense-response genes, phenylalanine ammonia lyase (PAL1-1), chalcone synthase (CHS2G), -1,3-glucanase (GLUC2-1) and chitinase (CHIT25-1) were examined by hybridization to PCR generated clones of the respective genes. Expression of each gene increased rapidly following inoculation with either fungus. Although differences were seen in response to the two pathogens, the general pattern was similar in resistant and susceptible cultivars. The results imply that factors other than the level or timing of active defense responses account for the cultivar differences seen when the plants are challenged at the time of flowering. 2004 Elsevier Ltd. All rights reserved.
