PATHOGENIC POTENTIAL OF THE ROOT-KNOT NEMATODE, MELOIDOGYNE INCOGNITA, ON RICE IN VENEZUELA

An experiment was carried out in a glasshouse to investigate the effect of increasing densities of three Venezuelan populations of Meloidogyne incognita on growth of rice. Initial nematode densities were 0, 0.25, 0.5, 1, 2, 4, 8, 16, 32, 64 and 128 eggs and juveniles/cm³ soil for the population from Zulia and 0, 2, 8, 32, 64 and 128 eggs and juveniles/cm³ soil for the populations from Barinas and Lara. Tiller height was recorded at five different plant stages and fresh plant weight and nematode populations in roots and soil per pot were determined at harvest. The population from Lara State was the most aggressive; all plants in pots inoculated with 128 nematodes/cm³ soil were yellowing at emergence and died 40 days later. Tolerance limits, derived according to Seinhorst, for shoot weight and tiller height of rice were 8 and 6.6, 6.6 and 4, 2.4 and 3.5 eggs and juveniles/cm³ soil for the Zulia, Barinas and Lara populations, respectively. A minimum relative yield of 0 could have been achieved at 512-420 and 156-226 eggs and juveniles/cm³ soil, for plant weight and shoot height, for the Zulia and Lara populations, respectively. Maximum reproduction rates of the nematode were 50, 19.5, and 57-fold and the equilibrium densities were 119, 256 and 62 eggs and juveniles/cm³ soil, respectively, for the populations from Zulia, Barinas and Lara.