Population distribution of Helicotylenchus species on Parkia biglobosa (Jacq) Benth and its association with some horticultural crops in Southern Guinea Savanna Ecological Zone of Nigeria

Abstract: The African locust bean (Parkia biglobosa Benth) is a perennial, deciduous fruit tree that is important for its myriad medicinal and nutritional benefits. The association of the spiral nematodes of the genus Helicotylenchus spp. with P. biglobosa has not been previously reported in Nigeria. Three P. biglobasa trees from University of Ilorin in the Guinea Savanna Ecological zone of Nigeria were purposively selected for nematode sampling for a period of five months (May to September). Eighteen field and horticultural crops were also surveyed to assess the population density of Helicotylenchus spp on selected agricultural crops in the local environment. Soil samples were collected monthly from the rhizosphere of P. biglobosa trees and also from the field crops to a depth of about 15 cm and within a 25 cm radius from the base of the plants. Vermiform nematodes were extracted from 250 g each of the composite samples using a modified Baermann extraction tray set-up. The spiral nematodes were frequently encountered in association with all the crops. Higher soil population of Helicotylenchus spp was recorded on Celosia argentea, Colocasia esculenta and Azadirachta indica at relative densities of 55.33, 42.11 and 25.6, respectively. The African locust bean trees also supported population build-up of Helicotylenchus spp which were found at a frequency rating of 100% in all the soil samples. Higher soil population of Helicotylenchus spp were recorded in June and September, coinciding with the two rainfall peaks while lower nematode population was recorded in August, at the lowest ambient temperature. The study indicated spiral nematodes as abundant and often associated with many agricultural crops at University of Ilorin, Guinea savanna of Nigeria. P. biglobosa was a suitable host for Helicotylenchus spp while the rainfall pattern and temperature changes influenced the population distribution of soil nematodes in the local environment.