Crudely-milled soil amendments of South African medicinal plants suppress population densities of Meloidogyne incognita race 2 and enhance vegetative growth and yield of tomato under microplot and field conditions

The nematode-suppressive and plant growth-increasing effects of crudely-milled stems, leaves and buds of five plant species ( Tabernaemontana elegans , Maerua angolensis , Cissus cactiformis , Synadenium cupulare and Euphorbia ingens ), used in South Africa by traditional healers as so-called “muti”, were examined under microplot and field conditions. In the microplot experiment, the soil amendments of T. elegans M. angolensis and C. cactiformis significantly suppressed the total number of eggs and J2 of Meloidogyne incognita race 2 in the roots of infected tomato plants by 82–97% compared with the untreated control plants. No significant differences were observed on the nematode-suppressive effect of these three plant species and the soil amendment of Cucumis myriocarpus and fenamiphos, the two reference treatments. In the field experiment, at all concentrations (5,10 15 g) included in the experiment, soil amendments of T. elegans M. angolensis and C. cactiformis plant species significantly suppressed the total number of nematode eggs and J2 in the roots by 83–87% compared with the untreated control plants. Soil amendments of T. elegans , M. angolensis , C. cactiformis resulted in a significant increase in various plant growth variables; shoot mass by 47–74%, fruit number by 8–46% and fruits mass by 28–31% compared with the untreated control plants in the field experiment. Although a few inconsistencies were observed, the nematode-suppressive effect of the soil amendments of T. elegans and M. angolensis were higher compared with the soil amendment of C. cactiformis , thus identifying the former two plant species as the best candidates for further studies. Our study confirms that plant materials derived from T. elegans and M. angolensis may offer an accessible and affordable management alternative to alleviate root-knot nematode problems in household and community gardens, and smallholder fields, especially in those provinces of South Africa (Mpumalanga, Limpopo and Kwazulu-Natal) were T. elegans and M. angolensis grow in abundance.