Population dynamics and association of plant-parasitic nematodes in the decline of Citrus Limettoides L. in West Bengal*

Seasonal variation in the population and vertical distribution of natural nematode populations (Helicotylenchus abunaomai, Hemicriconemoides cocophilus, Hoplolaimus seinhorsti, Caloosia parlona and Xiphinema insigne) were monitored in the rhizosphere of Citrus limettoides trees. The population density of different nematode species differed in the pattern of vertical distribution in relation to the state of decline of citrus trees. Population peaks were generally observed in August-September and in March-April. Moderately declined trees supported maximum populations of H. abunaamai and X. insigne suggesting their involvement with decline. But population levels of H. cocophilus, H. seinhorsti and C. parlona were maximum in healthy trees, suggesting their non-involvement with decline. The highest population density prevailed in the upper 20 cm soil depth and gradually the numbers declined in lower depths (20–40 and 40-60cm). Rainfall pattern, air and soil temperatures, soil moisture and host root growth appeared to be more predominant in influencing the population of pathogenically significant nematode species.