Submitted to: Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2009
Publication Date: N/A
Citation: N/A Interpretive Summary: Sorghum grain mold, a fungal disease, is a major problem in areas where frequent rains occur late in the season. The primary fungal species that cause mold in sorghum grain are Fusarium thapsinum and Curvularia lunata. Seeds infected with grain mold have lower yield and quality. In this study, 12 sorghum cultivars were sprayed with a mixture of F. thapsinum and C. lunata in the field and in the greenhouse. Cultivars Tx2911, Sureno, SC719-11E and SC650-11E were shown to have high levels of resistance to grain mold. Levels of PR-10 mRNA (a protein with anti-fungal properties) were measured in both resistant and susceptible sorghum lines to determine whether this protein contributes to resistance response to grain mold. The results showed that the high levels of PR-10 to sorghum grain mold may be a factor useful in breeding programs designed to combine multiple factors for resistance.
Technical Abstract: Differences in grain mold levels among different sorghum varieties grown in the same environment imply that genes play a role in controlling mold severity. The fungi most often recovered from naturally infected sorghum grain, Fusarium thapsinum and Curvularia lunata, were inoculated on a set of resistant and susceptible cultivars at anthesis and in both field and green house trials. In the field, 12 cultivars were inoculated with a mixture of F. thapsinum and C. lunata and in the greenhouse individual panicles from selected four cultivars were inoculated with spore suspensions of C. lunata, F. thapsinum or a mixture (a control of water (no spores) was also included). Based on grain mold severity (GMS) ratings and germination tests on the seed from the field trial, Tx2911, Sureno, SC719-11E and SC650-11E displayed a high level of resistance to grain mold. To determine if resistant and susceptible lines differed in active genetic response to the pathogens, PR-10 mRNA levels were measured using real time reverse transcriptase PCR, PR-10 is a protein with anti-fungal properties associated with a pathogen response product in sorghum. In field tests, most but not all cultivars showed significant induction of normalized relative quantities (NRQs) of PR-10 after dual inoculation with spores of both C. lunata and F. thapsinum. Under greenhouse controlled conditions, glumes of inoculated plants showed clear induction of PR-10 mRNA and the response was greater in resistant (Tx2911 and Sureno) than in susceptible (RTx430 and SC170-6-17) cultivars. Inoculation with spores from a single mold-inducing pathogen generally induced greater responses than when spores were combined. For RTx430, SC170-6-17 and Sureno, response to Curvularia lunata was greater and while Tx2911 showed a stronger response to F. thapsinum. The results indicate that induction of PR-10 in sorghum glumes may be a factor useful in breeding programs designed to combine multiple factors for resistance.