The susceptibility/resistance to Aphanomyces euteiches of various genotypes (cultivars and breeding lines) of several grain legume species was assessed in controlled conditions. A total of 279 genotypes from the major grain legumes grown in temperate climates (faba bean, chickpea, lentil, lupin and common vetch) and three other legumes frequently cultivated in France (French bean, clover and alfalfa) were screened with one pea-infecting isolate from France. Four different categories of susceptibility/resistance were identified among the legume species/cultivars tested with the pea A. euteiches isolate: (1) susceptible legume species (lentil, alfalfa, French bean) among which low levels of partial resistance was observed; (2) legume species including susceptible genotypes and genotypes with high levels of resistance (common vetch, faba bean and clover), (3) species with a very high level of resistance (chickpea) and (4) species displaying no symptoms (lupin). It is therefore important to consider pathogen-species and pathogengenotype interactions when defining the host specificity of A. euteiches and considering the possible role of different legume species in increasing or decreasing the soil inoculum potential.

The consequence of 10 successive monocultural cycles involving different legume species ⁄ cultivars on the inoculum potential (IP) of soils naturally infested by Aphanomyces euteiches was investigated under greenhouse conditions. The results showed that the IP of a soil naturally infested by A. euteiches can be significantly modified not only by the non-host or host status of crop species but also by the level of resistance of the cultivar. Susceptible species ⁄ cultivars (pea, lentil and susceptible cultivars of vetch and faba bean) are very favourable to pathogen multiplication, and continuous cultivation of each of these increased the IP values of a soil with a moderate initial IP (from 1AE9 to 3AE5 after 10 cycles). Conversely, non-host species and resistant cultivars of vetch or faba bean contributed to reducing the IP values of soils irrespective of the initial IP (from 1AE9 to 0AE5 and from 4 to 2, respectively, after 10 cycles). Aphanomyces root rot severity values on the resistant legume species ⁄ cultivars were not affected by the successive cultural cycles. This study, which showed that the IP of A. euteiches in soil can be reduced by planting appropriate legume species and cultivars in greenhouse conditions, will be useful for defining better crop successions for legumes.