The role of alkaloids in conferring aphid resistance in yellow lupin (Lupinus luteus L.)

A key goal in the breeding for aphid resistance of cultivated lupins is to manipulate the levels and distributions of alkaloids. Lupin alkaloids are known to be responsible for resistance to herbivorous insects, but the total seed alkaloid level must remain under 0.02% for animal and human consumption. Yellow lupin (Lupinus luteus L.) is being investigated as a new legume crop for Western Australia (WA), but most lines produced to date have been very susceptible to aphids. In contrast, breeders in WA have had ongoing success releasing narrow-leafed lupin (L. angustifolius L.) cultivars with adequate resistance to aphids. In this study, aphid performance was evaluated on yellow lupin plants in the glasshouse from an F2 population derived from a cross between Teo, a yellow lupin cultivar resistant to aphids and with high total alkaloid levels, and Wodjil, a single plant selection from Teo that is susceptible to aphids and has low total alkaloid levels, and their parents. Resistance in Teo and the F2 progeny was strongly associated with the alkaloids gramine and a gramine analogue. The absence of plants with intermediate levels of these alkaloids in progeny of this cross makes it unlikely that aphid-resistant lines can be generated using Teo as the resistance source. On the other hand, different alkaloids were correlated with aphid resistance in the narrow-leafed lupin cultivar Kalya, and aphid resistance was more evenly distributed among progeny of a cross of the resistant cultivar Kalya with the susceptible cultivar Tallerack. For this reason, additional yellow lupin lines with a more diverse alkaloid profile were selected for further study from the Australian lupin breeding program. A wide variation in the aphid tolerance among lines was observed and aphid tolerance was positively correlated with alkaloid content. However, four lines were identified with moderate levels of aphid resistance in a low alkaloid background. These lines had varying alkaloid profiles, but as expected none were dominated by gramine and its analogues. We believe these lines offer a greater opportunity for aphid resistance breeding in yellow lupins.