Hirschmanniella and other plant parasitic nematodes associated with lowland rice ecosystem in Laguna, Batangas and Central Luzon, Philippines and effect of weeds, moisture and flooding on off-season survival

The abundance and frequency of occurrence of Hirschmanniella spp. and other plant parasitic nematode genera associated with lowland rice were determined by collecting soil and root samples from farmers' rice fields in Laguna, Batangas, and Central Luzon [Philippines]. Hirschmaniella spp. were the major nematode pest associated with lowland rice areas with high frequency and abundance index. The two Hirschmaniella spp. identified were H. oryzae and H. mucronata, the former being more predominant and with higher population densities. Both species are adapted to similar type of ecological niches. This genus followed a negative binomial distribution pattern in rice field of Laguna. Higher population densities of these species were found in Batangas area. Tylenchorhynchus was second to Hirschmanniella in frequency and abundance. The other genera detected were Meloidogyne, Helicotylenchus, Rotylenchulus, Hemicycliophora, Criconemella, Pratylenchus, and Scutellonema. The population densities of Rotylenchulus, Criconemella, and Scutellonema decreased with increasing crop growth. H. oryzae is a potential economically important nematode pest of rice in all of the surveyed areas except in Tarlac and Pangasinan but it may become so with time and crops. H. mucronata was important only in Batangas but not in other provinces. Tylenchorhynchus may become important in all surveyed areas. Meloidogyne was important in Tarlac, whereas in other surveyed areas may be important except in Nueva Ecija. Helicotylenchus and Rotylenchus may be important in Batangas only. H. oryzae was most important among nematodes found in the surveyed areas, Batangas had the most nematode genera. Weeds and moisture level affected the off season survival of H. oryzae in the presence of rice stubbles. The nematode population densities in the soil drastically decreased with the increasing number of days after rice harvest up to 135 days irrespective of weeds and moisture treatments. Higher population of H. oryzae survived in roots than in soil after rice harvest. Root population of the nematode was also drastically reduced by drying than by moisture