Nematode community changes and survival rates under natural fallow in the sudano-sahelian area of Senegal

Summary The study was undertaken in the sudano-sahelian region of Senegal, south of the groundnut production area of Senegal. Millet fields, three fallow lands (exploited by the local population), 1, 9 and 18 years old at the beginning of the study, an 18 year-old fallow protected during the preceding 6 years by a fence, and a forest, were studied for 3 years. During the successive dry and rainy seasons soil samples were collected on 17 separate occasions to monitor plant parasitic and free-living nematodes. This study aims, firstly, to analyse the impact of the duration of the fallow on the nematode community, assuming that this management practice is known to be efficient in controlling plant parasitic nematodes, and secondly, if the dominance of certain nematode species in the agro-ecosystems was related to their ability to survive during the long dry season. The abundance of the plant parasitic nematode community did not change over the three-year period, but was greater in the 18–20 year-old fallows than in the younger ones or in the forest. Helicotylenchus dihystera and Scutellonema cavenessi were not affected by the dry season. H. dihystera had the highest survival rate followed by free-living nematodes, S. cavenessi and two species of Tylenchorhynchus. Species such as Xiphinema parasetariae, Aphasmatylenchus variabilis and Criconemella curvata could not be detected in the topsoil during the dry season. Survival rates of S. cavenessi decreased with fallow age (not in the forest) together with its populations, whereas it increased for all other species. The decreasing Tylenchorhynchus gladiolatus population in fallows of increasing age as well as the absence of H. dihystera in the millet fields could not be explained by a serious decrease of the survival rate during the dry season. These results demonstrated that nematodes could be controlled, without eradication, through a cultural strategy, which will favour the multiplication of weak pathogens of plant parasitic nematodes such as H. dihystera.

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