Numbers of Pratylenchus spp., (Nematoda) in the field on winter wheat in different cereal rotations

Numbers of mixed Pratylenchus spp. communities, including P. thornei, P. neglectus, P. penetrans and P. crenatus, were followed during two years on winter wheat in three locations in northern France. Pratylenchus spp. were most numerous on wheat after maize, and wheat monocultures had intermediate numbers. Sugar beet, when integrated as the previous crop, decreased populations of Pratylenchus; its effect was evident throughout the duration of the wheat crop, even on the 3rd wheat after sugar beet. The highest soil numbers occurred when wheat was at the 1-2-leaf stage. Most Pratylenchus were found in roots when wheat was beginning to tiller. In wheat/maize rotations, maize organic-matter restitution or soil compaction had little effect on Pratylenchus numbers. Wheat monoculture with straw ploughed into soil supported significantly fewer Pratylenchus than when straw was removed. Where Meloidogyne naasi was present, Pratylenchus was almost undetectable in the soil and the wheat roots; a negative correlation was observed between numbers of these two species in roots.