Effective stage of African marigold (Tagetes errecta L.) in reducing the root­ knot nematode (Meloidogyne incognita) Kofoid and White population in a tomato (solanum lycopersicon) crop in Ghana

Abstract

The aim of the study was to investigate the effective stage of the African marigold, Tagetes erecta, in suppressing root-knot nematode populations in Ghana. Two experiments were conducted in the plant house-/laboratory in 1999 and 2000 at the Kwame Nkrumah University of Science and Technology, Kumasi, Ghana. In the first and second experiments, different stages of T. erecta was investigated for nematicidal activity and hatching suppression of Meloidogyne incognita respectively. Data on nematodes were log transformed and subjected to analysis of variance using Genstat 8.1 .Population of second stage juveniles recovered from tomato protected by T. erecta was significantly lower than unprotected tomato (P< 0.05). Of the 1000 eggs of A/. incognita inoculated to tomato plants, 1273 juveniles were recovered from the control treatment, while just 62 juveniles were recovered from eight-week old tomato plants protected by T. erecta. Similarly, root gall index of tomato protected by T. erecta was significantly lower at eight weeks, which corresponded with the reduction in population at the same stage of growth. Fresh shoot and root and dry shoot and root weights of tomato plants protected by T. erecta were higher than unprotected plants. Root diffusates of T. erecta demonstrated significant hatching suppression activity against M. incognita eggs. The control treatments recorded 91 and 93 % hatching while ten-week old plants recorded 14 and 15 % hatching, representing significant hatching reduction of 85 and 84 % respectively. The effective stage of T. erecta in controlling M. incognita corresponded with eight to eleven weeks after germination.