EFFECTS OF WATER REGIME ON THE DISTRIBUTION OF MELOIDOGYNE GRAMINICOLA AND OTHER ROOT-PARASITIC NEMATODES IN A RICE FIELD TOPOSEQUENCE AND PATHOGENICITY OF M-GRAMINICOLA ON RICE CULTIVAR UPL R15

In a rice field toposequence including upland, rainfed lowland and irrigated rice, Meloidogyne graminicola was present in all three rice production systems, whereas Pratylenchus Zeae was present only in upland rice, and Hirschmanniella oryzae in flooded fields. The prevalence and mean intensity of M. graminicola were greater in flooded fields than in upland fields. In a greenhouse experiment, M. graminicola reduced the growth and yield of rice cv. UPL R15 when this cultivar was grown under upland conditions but not under irrigated conditions. M. graminicola is well adapted to irrigated conditions and shallow flooding does not affect its reproduction. However. shallow flooding reduced the percentage of roots damaged by the nematode, resulting in an absence of yield-reducing effect by the nematode under irrigated conditions.