Antibiosis and Tolerance Discovered in USDA-ARS Sorghums Resistant to the Sugarcane Aphid (Hemiptera: Aphididae)

The sugarcane aphid Melanaphis sacchari (Zehntner) was discovered infesting grain sorghum close to Beaumont, TX, near the Texas and Louisiana state line a few kilometers inland from the Gulf Coast in the late summer of 2013, and has been a perennial pest of grain, forage, and sweet sorghums. Our research was aimed at identifying sorghum germplasm that expresses host-plant resistance to the sugarcane aphid. We originally screened 36 lines including two known resistant sorghums (Tx2783 and DKS-37-07) and two known susceptible sources (WSH 117 and MORCH 858). From this screen, two pollinator lines (R. 11143 and R. 11259) developed by the USDA-ARS in Lubbock, TX, exhibited tolerance as indicated by damage ratings and growth characteristics, such as plant height, number of leaves, and chlorophyll content. Line R. 11143 had a slight net gain in chlorophyll content in the infested plants compared to the noninfested plants, indicating a highly tolerant sorghum. The R. 11143 and R. 11259 lines also expressed significant levels of antibiosis where net reproduction, number of nymphs produced in a day, intrinsic rate of increase, and the reproductive period in days were all significantly lower than all entries, with the exception of the known resistant controls DKS 37-07 and RTx2783. Pollinators R. 11143 and R. 11259 are recommended to be used in breeding programs for developing resistant sorghums threatened by the sugarcane aphid.