Effect of green manure plants on root knot nematodes infecting common beans

Abstract

Green manure plants are increasingly being adopted for soil fertility management especially in low-input agriculture. Information on their reaction to plant parasitic nematodes is, however, scanty. Green manure plants (Calliandra calothyrsus, Canavalia ensiformis, Chenopodium quinoa, Crotalaria juncea, Desmodium uncinartum, Gliricidia sepium, Leucaena leucocephala, Mucuna pruriens, Tephrosia purpurea, Tithonia diversifolia and Vicia villosa) were evaluated to determine their reaction to Meloidogyne javanica and M incognita. Their effects were evaluated in interplant, rotation and as amendments, under glasshouse and field conditions. Sesbania sesban and Tagetes minuta were included as susceptible and resistant checks, respectively. In the glasshouse, pots filled with steam sterilised soil was infested with 10,000 eggs and juveniles (h) ofM javanica. Completely randornised design with eight replications was used. The field experiments were conducted in a plot infested mainly with M javanica and M incognita and treatments were arranged in a randomised complete block design with four replications. Ninety days after planting, galling and egg masses were assessed on a scale of 1-9. Second stage juveniles were extracted i from the soil using the modified Baermann funnel technique. Differences in galling indices, egg mass indices and juvenile populations were significant among the green manure plants evaluated. The green manure plants were grouped into three categories with V. villosa, S. sesban and T. purpurea being rated as susceptible and having little or no effect on nematode populations and damage when used as soil amendments. Calliandra calothyrsus, C quinoa and C. ensiformis had galling indices lower than 3 and low reproductive factors and were placed in an intermediate category. They also resulted in intermediate effect on nematodes when used in rotation or interplanted with beans. All the other green manure plants (c. juncea, D. uncinartum, G. septum, L. leucocephala and T. diversifolia) had low galling indices and were not significantly different from T. minuta. They also reduced nematode damage and reproduction in rotation and interplant systems and when incorporated in the soil as green manures. Damage by nematodes and Meloidogyne juvenile numbers were highest on V. villosa and lowest on T. diversifolia, whereas high reduction in populations and damage on beans were observed where C. juncea was grown. Crotalaria juncea, and T. diversifolia can therefore be recommended for incorporation in cropping systems for root-knot nematode management in fields with high infestation.