Assessment of soil suppressiveness to Aphanomyces root rot of pea

The ability of field soils to suppress pea root rot caused by Aphanomyces e uteiches was assessed in field soil samples in a greenhouse bioassay and in field experiments sown with pea in monoculture for four years. In the bioa ssay, 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 w eeks 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 ye ar. A large variation in disease suppression was found in 24 arbitrarily ch osen 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, depen ding on the soil. In an experiment on a soil showing low disease suppressiv eness in the greenhouse bioassay, the crop failed in the second year, the n umber 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 d isease suppressiveness in the bioassay, the pea monoculture led to a slow b uild-up of oospores in root tissue and a steady high yield of 5,300 kg/ha t he fourth year.