Plant-parasitic nematodes associated with vegetable crops in Benin: relationship with soil physico-chemical properties.
Surveys were conducted in vegetable-producing communes of Benin between May 2004 and November 2005 to study the diversity and incidence of plant-parasitic nematodes affecting these crops and to assess the effects of soil physico-chemical properties on the nematodes. A total of 171 plant root and 171 soil samples collected from 26 vegetable crops were examined. Eleven species of plant-parasitic nematodes were recorded, of which six are reported for the first time in the country. When analyzed by crops sampled, communes surveyed and agro-ecological zones, the most frequently observed and widely distributed nematode species were root-knot nematodes, Meloidogyne spp., followed by Helicotylenchus dihystera and Scutellonema clathricaudatum. These nematodes infected 96.1, 76.9 and 53.9% of the crops sampled, respectively, and were observed on vegetable crops in 100, 94.4 and 44.4% of surveyed communes, respectively. Mean population density of Meloidogyne spp. (juveniles and males) was greater than that of the other nematode species. Prevalence, relative abundance and mean intensity were also higher for Meloidogyne spp. (79, 62.1 and 99.3%, respectively) than for other nematode species. The largest population densities of Meloidogyne spp. were observed in celosia, cucumber, green pepper, carrot, the African garden eggplant, okra, basil, and crin-crin (West African sorrel) (174, 103, 101, 98, 96, 96, 91, 79 nematodes/g sample, respectively). Correlation analysis indicated a weak relationship between soil physico-chemical properties and nematode population density (maximum value of the coefficient of correlation r=0.41). The results indicate that, apart from the direct influence of the host plant, soil properties play an important role in the abundance, distribution and structure of plant parasitic nematode communities. This validates the potential of nematodes as bio-indicator organisms of soil health.