Interaction Between Biotypes of the Spotted Alfalfa Aphid and Resistance in Alfalfa12

Abstract

The interaction between virulence in Therioaphis maculata (Buckton) and resistance in ‘Hayden’ and ‘Lahontan’ alfalfas was investigated. Evidence of a gene for gene relationship was found between biotypes (C, A, E, F, H) of the spotted alfalfa aphid expressing genes for virulence and in plants selected from Hayden expressing corresponding genes for resistance. This relationship was not evident between these same biotypes and plants selected from Lahontan alfalfa. The relationship in Hayden appears to be oligogenic (specific) since resistance to avirulent biotypes was not conferred in plants to virulent biotypes. The genic system in Lahontan was unusual and may be polygenic or oligogenic (general) since all plants selected for resistance to avirulent biotypes were equally resistant to virulent biotypes and vice versa. Lahontan alfalfa should be fully exploited so that these traits can be incorporated into alfalfa cultivars where polygenic resistance to the spotted alfalfa aphid is desired.