Sorghum (Sorghum bicolor) is one of the most important monocot crops cultivated worldwide and known for its versatility as a food, forage, and bioenergy crop. Sugarcane aphid (SCA; Melanaphis sacchari Zehntner) is considered a major threat to sorghum production, which severely damages the plant by sucking sap from leaves, thereby reducing its photosynthetic ability. Although several studies have been focused on identification of sorghum resistant/tolerant varieties to SCA, very little is known about molecular mechanisms underlying sorghum resistance/tolerance to SCA. In the current study, we screened a panel of sorghum nested association mapping (NAM) founder lines to identify and characterize sorghum resistance/tolerance mechanisms to SCA utilizing a blend of electrophysiological, biochemical, and molecular techniques. We identified sorghum genotype SC35 as the aphid-tolerant line among the different sorghum genotypes that displayed minimal plant biomass loss and a robust photosynthetic machinery, despite supporting higher aphid population. Phytohormone analysis revealed the well-coordinated interplay of phytohormones in SC35 plants which facilitate sorghum tolerance to SCA. Next, we found SC265 genotype demonstrates a combination of antibiosis- and antixenosis-mediated resistance mechanisms to SCA. SC265 had the higher constitutive and SCA feeding-induced levels of salicylic acid. Proteome profiling of SC265 after SCA infestation at days 1 and 7 revealed the suppression of plant defense-related proteins and upregulation of plant defense and signaling-related proteins, respectively. Overall, results from this work help us to better understand the mechanisms underlying sorghum resource allocation into tolerating aphid attack and defense signaling mechanisms against aphids.
