Spatial distribution of plant-parasitic nematodes in sugarcane fields

Abstract

Nematodes are important parasites of sugarcane in Brazil. Because of this, several studies have been conducted in recent years to evaluate the effectiveness of control methods. However, no studies have been reported on the spatial distribution of nematodes in sugarcane fields, and such studies are indispensable for the development of sampling plans, aimed at their application in integrated management programs. The spatial distribution of Meloidogyne javanica, Pratylenchus zeae, and mixed populations of P. zeae and P. brachyurus was studied in six commercial fields, with areas ranging from 0.26 to 0.50 ha; samples were obtained during the rainy season. The samples, represented by about 50 g roots, were collected within a rectangular grid measuring 7 × 12 m, 7 × 10 m or 5 × 13 m. Among the ten calculated semivariograms (four for M. javanica populations and six for P. zeae populations or the mixture between P. zeae + P. brachyurus), four could not be fitted to any model and presented a pure nugget effect; the spherical model showed the best fit to the semivariograms of data observed in the other six conditions. In those cases, values of range in semivariogram varied from 18 to 35 m, allowing the nematode aggregation area to be estimated at 2,110 m², on average, suggesting that at least five sampling points per hectare would be necessary, on average to obtain a reliable estimate for the population of these plant parasites in a given area.