A NEW GREENBUG VIRULENT TO E-BIOTYPE RESISTANT SORGHUM

Sorghum [Sorghum bicolor (L.) Moench] hybrids resistant to Biotype E greenbug [Schizaphis graminum (Rondani)] had more damage than expected when heavily infested with greenbugs during August, 1990. Greenbugs isolated from severely damaged plants of resistant sorghum in Stevens County, Kansas, were tested for virulence to Biotype-E resistant cultivars and lines of sorghum, wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), oat (Avena sativa L.), and rye (Secale cereale L.). Greenhouse tests involving seedling plants indicated that the sorghum lines with resistance to Biotype E were susceptible to the greenbug isolate from Stevens County. The only sorghum germplasm line that appeared resistant to this isolate was PI 266965. Small grains with resistance to Biotype-E greenbug retained their resistance to the new isolate. Because no previously designated biotypes have shown virulence to Biotype-E resistant sorghum the greenbug isolate from Stevens County was designated Biotype I. If Biotype I replaces Biotype E in the field, in a similar fashion to the replacement of Biotype C by Biotype E during the 1980s, greenbug resistance now available in sorghum will be compromised and sorghum production will be vulnerable to the new biotype.