Vertical distribution of nematode communities associated with sugarcane.

Nematodes induce high losses to sugarcane in Brazil, particularly in the sand soils of coastal tables, however there is little information on nematode diversity and distribution in swamp areas. The present study evaluated vertical distribution of nematode communities and the physical variables of soil: moisture and particle density in swamp area cultivated intensively with sugarcane in Pernambuco, Brazil. The nematode communities were characterized and the relationship among variables evaluated. Soil samples were collected horizontally in 40 points designing a 36x12 m net and vertically at 0-10, 10-20, 20-40 and 40-60 cm deep. Root samples were collected at 0-10 and 10-20 cm deep. The total of nematodes present was 369,392 per 300 cm 3 of soil, being 278,505 plant-feeding nematodes. The dominant plant-feeding nematodes were the genera Helicotylenchus (29.66%) and Pratylenchus (28.34%) and within the free-living nematodes was the taxon Dorylaimidae (21.23%). The ratio fungal-feeding/bacterial-feeding was 0.16. The ratio (omnivores+predators)/(bacteriophagous+mycophagous+phytoparasitic) was low (0.29), characteristic of annual crops. In general, nematode frequencies decreased as soil deep increased. Helicotylenchus was the nematode which more correlated with the other taxa. In soil, Pratylenchus was more frequent at 0-40 cm-deep and the taxon more affected by humidity. Soil moisture affected Pratylenchus, Criconemella, Dorylaimidae and Mononchidae frequencies negatively. In roots, population density of Pratylenchus increased as Meloidogyne density decreased, however, density of both endoparasites decreased at high precipitation level as in soil. Particle density of soil did not offer potential for use as indicator of nematode diversity in the area.