Fusarium Stalk Rot and Charcoal Rot Diseases Affect Nutritive Qualities of Grain Sorghum.

Stalk rots are among the most prevalent sorghum diseases worldwide. Although their impacts on quantitative yield losses are well documented, no experimental evidence has been reported on their potential effects on grain quality. We hypothesized that these diseases can have serious implications in terms nutritive qualities when grain sorghum is used in the feed and food industries. Hence, the objective of this study was to test the effects of Fusarium stalk rot and charcoal rot upon total grain protein, macro- (N, P, K), and micronutrients (Ca, Mg, Zn, Fe, Cu, Mn) content. Four genotypes were tested in the greenhouse and field against three Fusarium spp. (F. thapsinum, F. proliferatum, F. andiyazi) and Macrophomina phaseolina. Plants were inoculated at 14 d after flowering via injection. Panicles harvested at physiological maturity were measured for total seed weight (TSW). Ground and homogenized grain samples were used for nutrient analysis. Nitrogen was analyzed by sulfuric peroxide digest, while perchloric digests were used for other elements. Nutrients were statistically analyzed on a TSW basis. ANOVA revealed significant pathogen main effects on K, Ca, and Zn under greenhouse and field conditions, Cu and Mn under field conditions, and Fe under greenhouse conditions. Pathogen × genotype interaction effects were significant with significant pathogen simple effects on total protein, P, and Mg under both conditions, and Cu and Mn under greenhouse conditions. For most of the nutrients, pathogens had inconsistent effects across greenhouse and field conditions, revealing the effect of environment on the ability of different pathogens to manifest disease. However, most pathogens significantly and consistently reduced most of the nutrients analyzed in comparison to their counterpart controls (mock-inoculated with phosphate-buffered saline) under both conditions, demonstrating the general capability of the pathogens to reduce the nutritive value of grains despite the environment.