The virulence of 33 populations of Meloidogyne incognita collected from greenhouses under monoculture and crop rotation was studied to evaluate the influence of the cropping system on the selection of virulent biotypes in Uruguay, using bioassays including cultivars of tomato and pepper, resistant to M. incognita. Over thirty six percent of the populations were virulent on resistant tomato and pepper; 33.3% were virulent on resistant tomato, but not on pepper; 24.2% were avirulent on resistant cultivars of tomato and pepper and 6.1% were virulent only on peppers carrying resistance genes. There was a positive association between monoculture of resistant tomato or pepper and the presence of virulent populations of M. incognita.
