Assessment of Soil Suppressiveness to Aphanomyces Root Rot of Pea.

The ability of field soils to suppress pea root rot caused by Aphanomyces euteiches was assessed in field soil samples in a greenhouse bioassay and in field experiments sown with pea in monoculture for four years. In the bioassay, an inoculum of oospores in talcum powder was added to the test soils 1 week prior to sowing of pea seeds. The rate of infection was assessed 4 weeks after sowing. The field experiments were placed in six localities with varying degrees of soil suppressiveness to pea root rot and the pea yield and number of oospores of A. euteiches in root tissue were measured each year. A large variation in disease suppression was found in 24 arbitrarily chosen soils, sampled in the vining pea growing area in southern Sweden, and some soils were found to be strongly disease suppressive. The pea root rot development was also clearly different between the field experiments, depending on the soil. In an experiment on a soil showing low disease suppressiveness in the greenhouse bioassay, the crop failed in the second year, the number of oospores in root tissue increased rapidly over time, and no yield at all could be taken the fourth year. In contrast, on a soil with a high disease suppressiveness in the bioassay, the pea monoculture led to a slow build-up of oospores in root tissue and a steady high yield of 5,300 kg/ha the fourth year.

Prevalence and Pathogenicity of Foot and Root Rot Pathogens of Pea in Southern Scandinavia.

The occurrence of root pathogens of vining pea was determined in field surveys in Sweden and Denmark from 1989 to 1994. The most serious yield-reducing root pathogen, Aphanomyces euteiches, was found in approximately one-third of the sampled fields in both Sweden and Denmark. In a few fields severely infested with this pathogen, there was a total crop failure. The most frequently isolated pathogens were Phoma medicaginis var. pinodella and Fusarium solani; the latter also was isolated from vascular tissue up to the seventh node level. Other pathogens isolated from roots were F. avenaceum, F. oxysporum, F. culmorum, Chalara elegans, Pythium irregulare, and Mycosphaerella pinodes. In greenhouse pathogenicity tests, A. euteiches caused the most severe root damage and plant death of pea, followed by F. avenaceum and P. irregulare. There was an inverse relationship between field disease severity index and yield for fields infested with A. euteiches.