Mechanisms of resistance in three sorghum cultivars resistant to greenbug (Homoptera: Aphididae) biotype I

Three sorghum cultivars resistant to greenbug biotype I (Cargill 607E, PI550607, and PI550610) were evaluated to determine their mechanisms of resistance. Results indicated antibiosis and antixenosis were mechanisms of resistance in the 3 sorghum cultivars. PI550610 had the highest level of antibiosis, although this level was not significantly different from that in PI550607. Higher levels of tolerance in the biotype I-resistant cultivars, compared with the susceptible checks, were not detected. Proper use of these new sources of resistance will be important to reduce selection pressure for new greenbug biotypes. Sorghum cultivars exhibiting higher levels of tolerance should continue to be the focus of plant breeders because this mechanism may eliminate selection for new biotypes.