Evaluation of commercial sorghum hybrids for resistance to Melanaphis sacchari

During the 2015 season through field and growth chamber studies, grain sorghum, Sorghum bicolor, was evaluated for resistance to sugarcane aphid, Melanaphis sacchari (Zehntner), at three locations in Louisiana.  Hybrids included a known resistant ATx2752/RTx2783, a known susceptible ATx2752/RTx430, and 14 hybrids with suspected resistance. The objective of this study was to determine the degree of resistance among the hybrids. The field study was a split-plot design with hybrids being the main plot.  One sub-plot was protected from aphid infestation by means of insecticide Transform (sulfoxaflor), while the other was left untreated.  In addition to the field study, a seedling susceptibility screening was conducted with the same hybrids in a growth chamber.  Hybrid were planted in 8-inch pots, with five seedlings per pot.  At the 2 to 3 leaf stage, seedlings were infested with ~50 aphids per plant.  Each plot was rated on a 1-9 injury scale at 17 days after infestation.  In field trials under light to moderate aphid pressure, hybrids that appeared susceptible (demonstrated a yield benefit from sulfoxaflor applications) included: ATx2752/RTx430 and DG M756B39. Hybrids that exhibited possible tolerance (high aphid days but no yield benefit from spraying included: DG M77GB52, DG 765B, and R94153. Hybrids that exhibited possible antibiosis (low aphid days and no benefit from sulfoxaflor applications included: ATx2752/RTx2783, R84353, R9813, SP6929, SPX17514, SP7715, NKX760, P-83P17, W-844-E, and DKS37-07. Additionally, ATx2752/RTx2783, DKS37-07, R9813, R84353, SP7715, SPX17414, SPX17514, NKX760 and W-844-E exhibited significantly less aphid feeding injury than ATx2752/RTx430 in the seedling susceptibility screening.