Charcoal rot and Fusarium stalk rot diseases influence sweet sorghum sugar attributes

Abstract

Sweet sorghum [Sorghum bicolor (L.) Moench] is a prospective feedstock for the growing sugar-based bioethanol industry. Charcoal rot (Macrophomina phaseolina, MP) and Fusarium stalk rot (Fusarium thapsinum, FT) are fungal diseases of sorghum that reduce sweet sorghum sugar yields. The objective of this study was to investigate the impacts of MP and FT on sweet sorghum sugar concentration and yield. Field experiments were conducted with seven parental lines and 12 hybrids in 2014 and 2015. Plants inoculated with MP, FT, and phosphate-buffered saline (control) at 14 d after anthesis were harvested at 35 d after inoculation. Disease severity was measured using the number of nodes crossed by the lesion. Juice extracted from stalks was measured for volume. Juice sugar concentration (mg/mL) of sucrose, glucose, and fructose were quantified using HPLC and sugar yield (g/plant) was computed using juice volume and sugar concentrations. Treatment effects on sucrose concentration and yield, and total sugar yield (i.e., sucrose, glucose, and fructose) were genotype-specific while the effect of treatment on the yield of total and individual sugars was environment-specific. However, the environment×treatment effect was not significant for individual sugar concentrations. Stalk rot inoculations reduced sucrose concentrations to a significantly greater degree than glucose or fructose. Reduced sucrose concentrations and yields in the hybrids after inoculation were significantly and negatively correlated with the decrease of fructose. This suggested the enhanced conversion of sucrose to fructose after MP and FT inoculation. Overall, this study provided evidence for the adverse impacts of Fusarium stalk rot and charcoal rot diseases on sweet sorghum sugar attributes. These findings emphasize the importance of breeding sweet sorghum for enhanced stalk rot tolerance.