An investigation into the potential of crude and partially separated material of selected non–crop plant species as control agents of root–knot nematodes (Meloidogyne incognita) in tomato

Abstract

Plant-parasitic nematodes (PPN) are a serious problem in vegetable production and can cause severe damage to several crops. In rural, low-input farming nematode damage is much higher and yields can be completely destroyed. Some Commercial nematicides have been withdrawn from the market due to health and environment concerns. These need to be replaced by alternative nematode control strategies of which soil amendments is one alternative. Nine non-crop plant species used in various forms in traditional healing, viz. Cassia abbreviata, Cissus cactiformis, Euphorbia ingens, Ipomoea kituiensis, Maerua angolensis, Senna petersiana, Synadenium cupulare, Tabernaemontana elegans and Urginea sanguinea were screened under glasshouse conditions for their effect on the plant-parasitic nematode (PPN) (Meloidogyne incognita) on tomato. Subsequent assessments in microplots and in the field supported the glasshouse results in terms of suppression of root-knot nematode numbers with crudely milled soil amendments of C. cactiformis, M. angolensis and T. elegans. Tomato growth responses in these trials showed a tendency of phytotoxic effects after treatment of soil with crude leaf meal of E. ingens and S. cupulare. In the microplot study, the overall soil-amendment treatment effect was greater than that of three soil types on the performance of the tomato, although soil type might have had an effect on nematode suppression. Due to lack of correspondence between tomato leaf nutrient contents and the nutrient contents of the soil amendments it is suggested that these noncrop materials had negligible soil fertilization effects. In vitro bioassay studies confirmed that extracts of varying polarity of both plant products M. angolensis and T. elegans might be toxic to J2 stages of the root-knot nematode M. incognita. All extracts tested of M. angolensis caused immobility of J2, whereas only three extracts of T. elegans affected mobility of J2 adversely. Duration to 50 % effect, as well as extract concentration to cause immobility of the J2 varied but where movement ceased the J2 did not recover for up to 98 hours. This study has demonstrated the potential of locally available botanical materials for use as amendments in plant-parasitic nematode management and tomato growth and productivity improvement. This would particularly be true for small-scale application in subsistence agriculture. It is believed that these amendments could be used as control measures in integrated nematode control strategies. Their potential use could be adopted by small-scale farming communities, domestic gardeners and commercial farmers in the Mpumalanga, Limpopo and Kwazulu/Natal Provinces of South Africa where the relevant materials are available in useful quantities. Over-exploitation of natural resources should be avoided at all cost, however.