MSc

The rice cyst nematode, H. oryzicola is observed to be an important pest infesting the growth and yield of rice crop in Trivandrum District of Kerala. However; detailed study on the incidence of this nematode and the extent of crop loss caused by it on rice in Trivandrum District was not carried out earlier. The present work was hence undertaken to find out the localities of incidence of H. oryzicola, the extent of its population build up and their effect of infestation on the growth and yield of rice crop in the fields of Trivandrum District.
The incidence of H.oryzicola was observed in the soils and roots of rice from the fields of 21 Panchayats of Trivandrum District viz. Ulloor, Kazhakootam, Andoorkonam, Attipra, Vakkam, Chemmaruthy, Karavaram, Mudakkal, Nellanadu, Panavoor, Anadu, Aryanadu, Karakulam, Vilappil, Ottasekharamangalam, Aryancode, Vellarada, Perumbazhathoor, Parassala, Balaramapuram and Kalliyoor. The visual symptoms observed on the infested rice crop were reduced tillering, stunted growth of the plants, yellowing and chlorosis of the leaf and hollow brown roots with cyst/white females of H. oryzicola. The nematode is present throughout the season in the soils and roots of paddy, the highest population being in the second crop and lowest being in the third crop season. Their population build up between paddy varieties differ significantly, the highest population being in the long duration and lowest in the short duration paddy varieties. The nematode population also vary with soil types with a maximum in the sandy loam and minimum in the clayey soils.
The effect of transplanting of paddy in the H. oryzicola infested soils resulted in a gradual reduction in the population of their cysts from 15 DAT to 30 DAT than at transplanting and a gradual increase from 45 DAT to harvest than at 30 DAT. Similarly there was a significant reduction in the population of the larvae in the soil at DAT than at transplanting, a gradual increase from 30 DAT to 90 DAT than at 15 DAT and a significant reduction at harvest than at 90 DAT. In the paddy roots the number of cysts increased gradually as the plant grew; but the number of larvae increased gradually from transplanting attaining a maximum at 75 DAT and then reduced from 90 DAT to harvest than at 75 DAT. The infestation of H. oryzicola under field conditions on the rice crop caused considerable damage by reducing the number of tillers, percentage of productive tillers, plant height, shoot and root weights, panicle length and weight, total yield of paddy, wet and dry weights of grain and straw and by increasing the wet and dry weights of chaff.