Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2017
Publication Date: 11/15/2017
Citation: Bandara, Y., Tesso, T.T., Bean, S.R., Dowell, F.E., Little, C.R. 2017. Impacts of fungal stalk rot pathogens on physicochemical properties of sorghum grain. Plant Disease. 101(12):2059-2068. https://doi.org/10.1094/PDIS-02-17-0238-RE.
DOI: https://doi.org/10.1094/PDIS-02-17-0238-RE

Interpretive Summary: Stalk rot diseases are among the most ubiquitous and damaging fungal diseases of sorghum worldwide. The impact of stalk rot on yield is well known, but how stalk rot pathogens impact grain composition and physical properties is currently unknown. This study was conducted to determine if stalk rot diseases could alter grain mineral content, overall composition, and physical grain traits. The physical and chemical properties of sorghum grains are directly related end-use quality and directly impact utilization. Stalk rot pathogens did not impact grain hardness, did reduce macronutrients and most minerals. Specific high yielding hybrids were identified that resisted changes to macronutrients and minerals. This demonstrates that nutritionally stable hybrids and germplasm could be developed for use in areas where stalk rot is prevalent to prevent decreases in grain quality.

Technical Abstract: Stalk rot diseases are among the most ubiquitous and damaging fungal diseases of sorghum worldwide. Although reports of quantitative stalk rot yield losses are available, the impact of stalk rot on the physicochemical attributes of sorghum grain is currently unknown. This study was conducted to test whether stalk rot diseases could affect seed mineral content (N, P, K; Ca, Cu, Fe, Mg, Mn, Zn), macronutrients (protein, fat, starch), ash content, and physical traits (weight, hardness, diameter). Two field experiments were conducted with four sorghum genotypes (two hybrids and two lines). Plants from each genotype were inoculated with four stalk rot pathogens (Fusarium andiyazi, F. proliferatum, F. thapsinum, and Macrophomina phaseolina) and mock-inoculated control. Seeds collected from infected and control plants were analyzed for macronutrients and ash content using near-infrared reflectance spectroscopy (NIRS), seed physical traits using the single kernel characterization system (SKCS), and mineral content. Stalk rot pathogens did not significantly affect seed physical traits and therefore may not affect milling quality. Although stalk rot pathogens did not affect seed macronutrient and mineral contents when analyzed on a percent basis, effects became apparent when data were analyzed on a per unit grain and total seed weight per panicle basis. Pathogens significantly reduced all macronutrient and most mineral contents across genotypes and environments on a per unit grain basis with the exception of N and Mg, which were affected in a genotype- and environment-specific manner. Fe was not significantly affected. Most minerals tested were significantly and negatively correlated to disease severity (lesion length) and total seed weight per panicle. One of the high yielding hybrids, Pioneer 84G62, exhibited reduced mineral and macronutritional changes after stalk rot infection, providing insights into the possibility of producing high-yielding, nutritionally stable hybrids under stalk rot disease pressure through dedicated breeding efforts.