BIOCONTROL OF APHANOMYCES ROOT-ROT AND PYTHIUM DAMPING-OFF BY PSEUDOMONAS-CEPACIA AMMD ON 4 PEA CULTIVARS

Pseudomonas cepacia strain AMMD applied as a seed treatment has been used for biocontrol of Pythium damping-off and Aphanomyces root rot of peas. We tested the biocontrol efficacy of this strain on four pea cultivars that differed in susceptibility to Aphanomyces root rot. In 1990 and 1991, seedling emergence, Aphanomyces root rot severity, and pea yield of biocontrol-treated and nontreated controls were compared in a field naturally infested with Pythium spp. and Aphanomyces euteiches f. sp. pisi. In 1991, the experiment also was conducted in an adjacent field with no history of pea cropping to evaluate the effect of the biocontrol agent in the absence of Aphanomyces root rot. Biocontrol efficacy was not limited to a single cultivar. Differential effects of biocontrol among cultivars were clearly related to the degree of susceptibility of each cultivar to Pythium and Aphanomyces. Seed treatment with P. cepacia AMMD significantly improved emergence of all four cultivars when disease was severe and improved emergence of two cultivars when disease was moderate. P. cepacia AMMD did not reduce symptoms of Aphanomyces root rot in either year. Bacterial seed treatment increased yield of three cultivars in the infested field in 1990 when compared with no treatment but did not increase yield of any of the cultivars in the same field in 1991. Bacterial seed treatment increased yield of one cultivar in the noninfested field. A metalaxyl seed treatment included in experiments in 1991 to control Pythium increased both emergence and yield.