Genetics of Greenbug (Homoptera: Aphididae) Virulence to Resistance in Sorghum

Abstract

Greenbug, Schizaphis graminum (Rondani), biotypes C, E, and F were inbred, crossbred, and backcrossed with recessive testers under laboratory conditions to determine the inheritance of virulence to resistance in sorghum (Sorghum bicolor [L.] Moench). Each progeny was reared to adult and cloned during its parthenogenesis reproductive phase. Clones were. evaluated on three sorghum entries with greenbug resistance acquired from different germplasm sources. Greenbug virulence to biotype F-resistant 'Piper' was dominantly inherited and governed by a duplicate-dominant gene that was influenced by a third modifier gene. The modifier gene was epistatic to one of the duplicate genes when dominant. Virulence to biotype C- and E-resistant 'Pioneer 8493' with resistance from PI 264453 was also controlled by a duplicate dominant gene-modifier gene, but green bug virulence was recessive. The modifier gene Was also epistatic to one of the duplicate genes when dominant. In contrast, greenbug virulence to biotype C-resistant 'Pioneer 8515' with resistance from SA 7536-1 was recessive and simply inherited. No linkage occurred between the genes governing virulence to these resistant sorghum entries, regardless of biotype. The genes influencing virulence to a particular resistant sorghum, were found to be allelic among the biotypes. Specific greenbug virulence-sorghum resistance interactions followed a gene-for-gene relationship similar to those first reported in plant-pathogen interactions. Our results provide further evidence that genetic recombination during the green bug's sexual cycle can produce the biotypic variation inherent to this aphid.