EFFECTS OF HIGH NICKEL SOIL ON ROOT-KNOT NEMATODE DISEASE OF TOMATO

Abstract

High nickel (Ni) soils are becoming increasingly common where soils are exposed to waste products, and can be harmful to agricultural enterprises. In a study of tomato (Lycopersicon esculentum cv. Pusa Ruby) plants exposed to high soil Ni and nematodes, it was found that both interact to affect growth of young plants. Soils amended with Ni at 0, 10, 50, 100, 200 and 400 mg/L and subsequently inoculated with 2000 juveniles of Meloidogyne incognita/pot resulted in substantial growth reduction of tomato. Nickel amendments at 200 or 400 mg/L caused browning and/or necrosis of foliage. Either Ni or nematodes were able to decrease root and shoot growth, and carotenoid and chlorophyll contents of foliage. Nematode disease severity (i.e., degree of galling) increased when plants received a Ni amendment of 50 or 100 mg/L. Nematode reproduction (egg masses/root system) and size of soil population increased when soils were amended with 50 mg Ni/L. Higher concentrations of Ni amendments (200 and 400 mg/L) decreased number of galls, egg masses, fecundity and the soil population of M. incognita. Nickel contents of roots, stems and foliage were greater in nematode infected plants than uninfected plants grown in soils receiving no Ni amendments. The order of Ni accumulation was: root leaves stem, and leaves root stem in infected and uninfected plants, respectively. A small increase in root Ni concentration (up to 24 µg Ni/g dry root) was associated with increased juvenile penetration and gall formation of nematodes; however, further increases of Ni in roots (due to 200 and 400 mg Ni treatments) suppressed nematode pathogenesis. This interaction between M. incognita and Ni on dry matter of plant organs was found to be concentration dependent, with the interaction being synergistic at 50 mg/L, but at 400 mg Ni the effect was antagonistic with regard to the effect of Ni on nematodes and plant growth.