NEW SOURCES OF RESISTANCE TO GREENBUG, BIOTYPE-I, IN SORGHUM

The greenbug [Schizaphis graminum (Rondani)] has been a major pest of sorghum [Sorghum bicolor (L.) Moench] since 1968, and several biotypes have evolved. Except for PI 266965 [S. halapense (L.) Pers., a tetraploid] and Cargill hybrid 607E, all previously reported sources of resistance to the widespread Biotype E are susceptible to Biotype I, a new biotype first reported in Kansas in 1990. Greenbug is a serious pest in Russia. To determine whether Russian sorghum contains resistance to Biotype I, 110 germplasm accessions obtained from Krasnodar Province in the fall of 1991 were assessed for their reaction to Biotype I greenbug. In two replicated growth chamber tests using individually caged plants, 10 accessions (3 grain sorghum and 7 sudangrass types) showed significantly higher (P = 0.05) levels of resistance than did the susceptible check when rated 13 to 14 d after infestation. The accession showing greatest resistance, PI 550610, a durra grain type originally from Syria, showed a level of resistance equal to that of the resistant hybrid check.