The reaction of soybean and other legume crops to root-knot nematodes (Meloidogyne spp.), and implications for growing these crops in rotation with sugarcane

The reaction of soybean, mungbean, peanut, lablab, cowpea and velvet bean to two species of root-knot nematode (Meloidogyne javanica and M. incognita) was assessed by bare fallowing a field after sugarcane harvest and planting the legumes 4 and 12 weeks later. Leichhardt, the most widely grown soybean cultivar in the Queensland sugar industry and three other soybean cultivars were included whereas the other legumes were represented by only one cultivar. The severity of nematode galling was assessed 7 weeks after planting and final nematode population densities were measured at similar to 14 weeks. The roots of mungbean, lablab and all soybean cultivars except cv. Stuart were severely galled by root-knot nematode at both planting times; however, because root-knot nematode populations declined rapidly in the bare fallow that followed the sugarcane harvest, galling was less severe in the second planting compared with the first planting. Peanut, velvet bean and cowpea cv. Meringa showed little or no nematode damage at either planting time. Final nematode population densities were relatively high following the heavily galled crops but were similar to an adjacent bare fallow after peanut, velvet bean and soybean cv. Stuart. In a separate glasshouse study, soybean cv. Leichhardt was badly damaged by a population of M. incognita from the field site but was relatively tolerant to M. javanica and a population of M. incognita from another region (Bundaberg). In another glasshouse test, M. javanica and the Bundaberg population of M. incognita did not increase significantly on soybean cv. Leichhardt or a range of tropical soybean lines after 8 weeks. These results indicate that soybean is generally suitable for rotation with sugarcane but that local populations of root-knot nematode may damage certain cultivars in sandy soils.