Efficacy of pyramiding greenbug (Homoptera : Aphididae) resistance genes in wheat

Durable resistance to greenbug, Schizaphis graminum (Rondani), in wheat is a goal of wheat improvement teams, and one that has been complicated by the regular occurrence of damaging biotypes. Simulation modeling studies sugge st that pyramiding resistance genes, i.e., combining more than one resistan ce gene in a single cultivar or hybrid, may provide more durable resistance than sequential releases of single genes. We examined this theory by pyram iding resistance genes in wheat and testing a series of greenbug biotypes. Resistance genes Gb2, Gb3, and Gb6, and pyramided genes Gb2/Gb3, Gb2/Gb6, a nd Gb3/Gb6 were tested for effectiveness against biotypes E, F, G, H, and I . By comparing reactions of plants with pyramided genes to those with singl e resistance genes, we found that pyramiding provided no additional protect ion over that conferred Ly the single resistance genes. Based on the result s of this test, we concluded that the sequential release of single resistan ce genes, combined with careful monitoring of greenbug population biotypes, is the most effective gene deployment strategy for greenbug resistance in wheat.