The effect of Pratylenchus zeae on the growth and yield of upland rice.

Abstract

The root lesion nematode Pratylenchus zeae is widely distributed on upland rice but its economic importance has not been assessed. In a field trial, following a five month clean fallow, the control of P. zeae using carbofuran, increased the yield of cv. Upl Ri-5 whilst the yield of cv. Kinandang Patong was unaffected. Pre-sowing soil population densities (Pi) of P. zeae were low (0-1 11 nematodes/lOO ml soil) and there were no obvious symptoms of infection during early vegetative growth although the plant height of Upl Ri-5 was slightly reduced. At harvest the yield of treated plants was increased by 13-29 O/O of that of untreated plants having a mean infection of 1 350 nematodedg root (P < 0.05). In the glasshouse the rate of growth and tillering of cv. IR36 was significantly reduced with a high Pi (630-3 O00 nematodesllO0 cm3 soil). Infected root systems were stunted and mean root fresh weight was reduced by 40-60 %. Although infection reduced the no. of spikeletslplant, these plants had a higher harvest index and consequently grain yield was unaffected. The relationship between yield and the population density of P. zeae at different crop growth stages, in the field indicates low tolerance and a high relative minimum yield of 65 O/o. RESUMÉ Influence de Pratylenchus zeae sur la croissance et la récolte du riz de plateau Pratylenchus zeae est très répandu sur le riz de plateau mais son importance n'a jamais été évaluée. Aux Philippines, un essai au champ mis en place après cinq mois de jachère nue indique que les traitements nématicides contre P. zeae provoquent une augmentation de la récolte du cv. Upl Ri-5 mais n'affecte pas celle du cv. Kinandang Patong, tout aussi sensible à ce nématode.