Effect of plant parasitic nematodes on the sustainability of a natural fellow cultural system in the Sudano-Sahelian area in Senegal

To study the influence of fallow on plant parasitic nematodes and soil fert ility, the difference in the growth of millet in a greenhouse was compared in sterilized and naturally infested soil. These soils are ferruginous and were taken from a 17-year-old fallow plot and a neighbouring cultivated fie ld, located in the region of Thysse Kaymor in Senegal. The plant-parasitic nematode community of the previously cultivated soil consisted primarily of two species: an ectoparasite, Tylenchorhynchus gladiolatus, and an endopar asite, Scutellonema cavenessi. The soil from the fallow plot was infested w ith many species, but under the influence of the millet crop, it evolved to wards the two species situation observed in the cultivated soil, except tha t under the experimental conditions (in pots), Pratylenchus pseudopratensis replaced S. cavenessi. Whether or not the soil was infested with nematodes , the previous fallow period had a positive effect on the development of su ccessive millet crops. The impoverishment of the soil through repeated cult ivation and the impact of nematodes both reduced crop growth. The two facto rs evolved in the same way, that is a decrease in the development rate of t he millet as the number of crop cycles increased. The symptoms of soil impo verishment can be corrected, either by suppressing the nematodes or by fall owing. (C) 2000 Editions scientifiques et medicales Elsevier SAS.