Passive transport of phytoparasitic nematodes by runoff water in the Sudano-Sahelian climatic area

The aim of the work was to quantify the role of runoff in nematode transpor t, compared with soil particle transport, during the rainy season in the Su dano-Sahelian area. The measurements were made at the outlet of a 58 ha wat ershed located in the Nioro du Rip region, south of the Senegalese peanut-g rowing basin. Every time the rainfall was sufficiently strong to cause a ru noff, water was collected to estimate the volume of runoff, the soil partic les and the nematode contents. Soils in the different agronomic areas were also collected to determine the nematode infestation. Some 6000 m(3) of wat er run off during the rainy season, together with 18.6 t of soil and 279.5 million of nematodes, 127 million of which were major phytoparasitic specie s. The transport of the different species was not uniform. The first five r unoff episodes supplied one-half the volume of runoff water and transported approximately half the phytoparasitic nematodes, but nearly three-quarters of the solid particles. Fifteen percent of the nematodes were transported during the intermediate stage of the rainy season. and approximately 30% du ring the final period, with equivalent water proportions but smaller quanti ties of soil. Of the 15 genera and species observed in the area, Tylenchorh ynchus gladiolatus, Scutellonema cavenessi, Helicotylenchus dihystera and G racilacus parvula represented 87% of the soil population, 61% being account ed fur by the first two species. The average proportions of T. gladiolatus or G. parvula in the runoff water were greater than those in the soil, whil e the opposite was true for S. cavenessi, P. pseudopratensis and T. mashhoo di. H. dihystera was equally represented in both the soil and runoff water. The consequences of this "biological erosion'' on the field infestation an d on the cultural system based on fallowing are discussed. (C) 1999 Elsevie r Science B.V. All rights reserved.