Antixenosis and antibiosis mechanisms of resistance to turnip aphid, Lipaphis erysimi (Kaltenbach) in Brassica juncea-fruticulosa introgression lines

Lipaphis erysimi is a key pest of rapeseed-mustard in Indian subcontinent. Although chemical control is the basis of its management, the unsustainability of this approach has accelerated global research efforts to find alternate solutions. Host plant resistance is one among these. A set of introgression lines were developed using Brassica fruticulosa previously found to be resistant to L. erysimi. Rigorous screening over the years led to the identification of 3 introgression lines (I8, I79, and I82) for field resistance to aphids. We evaluated these introgression lines under field and laboratory conditions along with B. fruticulosa (resistant parent), B. juncea var. PBR-210 (susceptible parent) to elucidate the mechanism of resistance. Significantly a smaller number of aphids settled on circular leaf discs of B. fruticulosa, I8 and I82 compared to that on PBR-210 after 24 and 48 h of release. A similar trend was observed in free choice field experiment with significantly less aphid colonization on B. fruticulosa, I8, I79 and I82 compared to PBR-210 indicating lower aphid preference for these genotypes. Further, no choice experiments revealed significant negative effects of these genotypes on aphid demographic parameters (nymphal survival, development period, fecundity and longevity). Tolerance may not be a mechanism of resistance as aphid population failed to develop on these genotypes. Thus, resistance in these introgression lines may be attributed to a synergistic combination of antixenosis and antibiosis mechanisms.