Large-scale density-based screening for pea weevil resistance in advanced backcross lines derived from cultivated field pea (Pisum sativum) and Pisum fulvum

The pea weevil, Bruchus pisorum, is one of the most intractable pest problems of cultivated field pea (Pisum sativum) in the world. Pesticide application, either as a contact insecticide spray to the field pea crop or fumigation of the harvested seed, is the only available method for its control. The aim of the study was to develop a quick and reliable method to screen for pea weevil resistance and increase efficiency in breeding for this important trait. Backcrossed progenies derived from an interspecific cross between cultivated field pea and its wild relative (Pisum fulvum, source of resistance for pea weevil) were subjected to natural infestation in field plots. Mature seeds were hand-harvested, stored to allow development of adult beetles, and then separated into infested and non-infested using a density separation method in 30% caesium chloride (CsCl). Susceptibility and resistance of the progenies were calculated based on this method and further confirmed by a glasshouse bioassay. Resistance in backcross populations improved considerably through selection of resistant lines using the density separation method. We found that the method using CsCl separation is a useful tool in breeding for pea weevil resistance. We were able to introgress pea weevil resistance from P. fulvum into cultivated field pea through backcrossing to produce several advanced pea weevil resistant lines following this procedure.