Selection for resistance against root pathogens in a pea composite cross

The possibility of improving resistance in pea against the root pathogen Aphanomyces euteiches using composite cross as a breeding and selection method was examined. In order to maintain acceptable agricultural features and high yield 6 out of the 8 parental varieties in the present composite-cross were commercially grown varieties. Populations of the composite cross were grown up to five generations with selection pressure in soil heavily infested with pea root pathogens or without selection pressure on soil free of pea root pathogens. Yield of populations of the F9 and F10 generations of the composite cross grown with selection pressure was on average 35% higher than that of the population obtained without selection pressure as well as the average yield of the 8 parentals of the composite cross, which were of similar magnitude. In healthy soil the yield was overall higher than in the pathogen-infested soil, but yield did not differ between the populations from the composite cross with and without selection pressure, which were also similar to the average yield of the 8 different parentals. Recombinant inbred lines (RILs) randomly selected from the F10 population with selection pressure developed 23% less root rot than the corresponding F10 population without selection pressure, when grown in field soil heavily infested with pea root pathogens. Surprisingly, greenhouse pot experiments with pure cultures of the pea root pathogen A. euteiches resulted in higher root disease, in RILs from populations with selection pressure than from corresponding RILs without selection pressure. Problems related to greenhouse screening for resistance is discussed as well as the possibilities of using composite cross as a method to improve resistance against root diseases in grain legumes.