The response of tobacco varieties to infection by maloidogyne species in relation to nematode occurrence and infestation in Busia and Bungoma districts of Kenya.

Abstract

The occurrence and infestation of plant-parasitic nematodes on tobacco, Nicotiana tabacum L., in Busia and Bungoma districts of Kenya was investigated. during 1983. Samples of tobacco roots and soil from 238 different sites were examined. The nematodes were extracted by the Baermann's pan and filter method, and then, identified to genus, except for rootknot nematode, Meloidogyne Goeldi, which was identified to species level. The response of tobacco varieties; air-cured "Burley 181';; fire-cured "Heavy Western" and flue-cured "Speight G28", to increasing infestation levels of rootknot nematodes, were determined in 60 different plots of either small-holder farmers or the tobacco company, B.A.T. (Kenya) Limited. Similar studies were also done on potted plants under glasshouse. ( Some seven genera of plant-parasi tic nematodes were commonly found associated with tobaeco roots. They were; rootknot nematode, Meloidogyne spp., root lesion nematode, Pratylenchus spp., stubby root nematode, Tylenchorhynchus spp., spiral nematodes; Scutellonema spp., Helicotylenchus spp. and Rotylenchus spp., and sheath nematode, Hemicycliophora spp. The rootknot nematode caused conspicous galls 01:'1 tobacco roots, and severa]Y

infected plants were considerably stunted in growth. The nematode was found to be present in all the sites sampled, and it contributed upto about 85% of the total population count of parasitic nematodes within and around tobacco roots at postharvest sampling. The specie Meloidogyne j avanica (Treub. ) Chitwood was predorminant wi th an incidence of 85%. ~.incognita (Kofoid and White) Chitwood made up the remaining 15%. On field plots where the preplant infestation levels of rootknot nematodes ranged from 5.9 to 10.2 larvae per 100 g of soil, the tobacco plants on sandy or gravel soils were more severely galled and stunted, relative to those on clay soils. Nematicide trials with phenamiphos at 10 Kg, a.i., per ha, on paired plots of tobacco always gave significantly (P = 0.05) better plant growth on sandy soils but not always on clay soils. Inspite of considerable galling of roots, the nematodes apparently caused relatively less reduction of growth and yields of tobacco plants in clay soils. Similar results occurred on potted pIants as well. Tobacco variety "Speight G28" was more tolerant to i~fection by rootknot nematodes at increasing infest ation levels, relati ve to varieties "Burley 181" and "Heavy Western". The latter two were usually equally galled and stunted at similar inoculum levels.