Submitted to: Journal of Agriculture and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/1/2004
Publication Date: 1/1/2005
Citation: Prom, L.K., Waniska, R.D., Kollo, A.I., Rooney, W.L., Bejosano, F.P. 2005. Role of chitinase and sormatin accumulation in the resistance of sorghum cultivars to grain mold. Journal of Agricultural and Food Chemistry. 53(14):5565-5570. Interpretive Summary: Grain mold of sorghum is most severe in areas with frequent rains close to harvest time. Seeds infected with grain mold have lower yield and quality. Fusarium thapsinum and Curvularia lunata are the two most common fungal species associated with moldy grain in the United States. The levels of antifungal proteins like chitinase and sormatin are said to affect the amount of disease in sorghum lines. In order to develop cost-effective control methods, it is important to know the relationship between resistance to grain mold as measured by the amount of infection, germination, and kernel weight, with the levels of chitinase and sormatin in seeds of different sorghum cultivars. Eight sorghum cultivars were tested with each fungus and a mixture of the two fungi. The amount of chitinase and sormatin were obtained from seed samples collected at 30 and 50 days after the sorghum heads were sprayed with the pathogens. In both years, levels of chitinase increased in cultivar 98LB723 and decreased in Dorado. Generally, the levels of sormatin decreased in all cultivars tested. This study showed no definite relationship between resistance to grain mold and the amount of these antifungal proteins in sorghum seeds.
Technical Abstract: Experiments were conducted to determine the association between resistance to grain mold and the accumulations of chitinase and sormatin. Eight sorghum lines were treated at 50% bloom with Fusarium thapsinum, Curvularia lunata, a mixture of the two fungi, and a water-sprayed control. At maturity, percent disease severity, seed germination rates, and kernel weight were recorded. Chitinase and sormatin content (mg/g dry weight) were measured in seed samples taken at 30 and 50 days after treatment (DAT). Seed chitinase content was moderately affected by sorghum line (P= 0.10), and significantly affected by the developmental stage of the kernels (P= 0.05). Sureno, a grain mold moderately resistant sorghum line and the moderately susceptible lines 98LB650, and 98LB723 exhibited a larger negative change in chitinase content at 50 DAT, over water-sprayed control treatment at 30 DAT, seed germination and sormatin content at 50 DAT, and between seed germination and kernel weight. There also was a significant positive correlation between germination and chitinase content at 30 DAT. No association between disease severity and changes in chitinase content at 50 DAT was observed. Sormatin content also was significantly affected by the stage of kernel development. Sorghum cultivars inoculated with fungal pathogens responded differently as indicated by the significant sorghum line x treatment interaction for sormatin content in 2000. In both years, larger increases in sormatin content over the water-sprayed control treatments were observed on moderately susceptible to susceptible cultivars such as 98LB650, 98LB723, 98LB789, RTx430, and RTx2536 than on Sureno. Except for percent disease severity and germination, there was no significant association between all the other parameters measured in 2001. The results of this study did not clearly demonstrate a strong association between resistance to grain mold and the accumulation of sormatin and chitinase.