Spatial and Temporal Distribution of Plant-Parasitic Nematodes on Pigeonpea in Alfisols and Vertisols

Populations of Heterodera cajani, Rotylenchulus reniformis, and other plant-parasitic nematodes associated with field-grown pigeonpea (Cajanus cajan (L.) Millsp.) were monitored monthly for 12 months at three depths in alfisol and vertisol soils. Heterodera cajani and R. reniformis were the predominant nematodes in the vertisol and the alfisol, respectively. Hoplolaimus seinhorsti and R. reniformis in alfisol, and H. cajani, Helicotylenchus retusus, and R. reniformis in vertisol, were 0-45 cm deep throughout the year. Populations of Pratylenchus zeae and H. seinhorsti declined with sampling depth. Cysts of H. cajani, however, were found at a soil depth of 75-90 cm. Highest population densities of R. reniformis and H. cajani occurred at crop maturity and harvest (January-February). Summer fallow (February-June) reduced R. reniformis populations 70% and 36% at 0-15 cm and 15-30 cm depths, respectively. Summer fallow reduced densities of H. cajani juveniles by 45% at 0-15 cm but densiti