Stalk Rot Diseases Impact Sweet Sorghum Biofuel Traits

Owing to its sugar-rich stalks and high biomass, sweet sorghum Sorghum bicolor (L.) Moench] has potential as a source of biofuel feedstock for juice and lignocellulosic-based bioethanol production. However, stalk rot-mediated lodging is an important concern. The potential impacts of disease on sweet sorghum biofuel traits are currently unknown. The objectives of this study were to test the effects of Fusarium stalk rot and charcoal rot on sweet sorghum biofuel traits and to assess the combining ability of the parental genotypes for resistance to the two diseases. Nineteen genotypes including 7 parents and 12 hybrids were tested in the field in 2014 (Ashland, Kansas) and 2015 (Manhattan, Kansas) against Fusarium thapsinum (FT) and Macrophomina phaseolina (MP). Fourteen days after flowering, plants were inoculated with FT and MP. Plants were harvested at 35 days after inoculation and measured for disease severity using stalk lesion length. Grain weight, juice weight, Brix (°Bx), and dried bagasse weight were also determined. Total soluble sugars per plant (TSSP) were determined using juice weight and °Bx. On average, FT and MP resulted in reduced grain weight and dried bagasse weight by 17.4 and 17.6 %, respectively, across genotypes. Depending on the genotype, pathogens reduced juice weight, °Bx, and TSSP in the ranges of 11.3 to 25.9, 0.2 to 16.7, and 21.2 to 33.3 %, respectively. Parental line general and specific combining abilities were found to be statistically insignificant. This study revealed the adverse effects of stalk rot diseases on harvestable biofuel traits and the need to breed sweet sorghum for stalk rot resistance.