Relationship between soil properties, crop management, plant growth and vigour, nematode occurrence and root damage in East African Highland banana-cropping systems: a case study in Rwanda

Parasitic nematodes are widespread in Musa cropping systems in African lowlands where they are known to limit crop production. However, their distribution is very poorly known in the large parts of the East African Highland banana ecology. We carried out a survey in 188 fields in Rwanda to assess and understand nematode occurrence and damage under a wide range of agro-ecological conditions. Altitude varied from 900 to 1800 m above sea level and soil types were distinctly different in the five eco-regions sampled and derived from diverse parent materials; i.e., Ruhengeri (Andosol), Gitarama-Butare (Acrisol), Kibungo (Nitisol), Gashonga (Ferralsol) and Bugarama (Fluvisol and Vertisol). Crop management practices, root health parameters and nematode infection in roots were recorded for a single East African highland banana cultivar (Intuntu, AAA-EA). Plant-parasitic nematodes from five genera were identified: Pratylenchus goodeyi, Helicotylenchus multicinctus, Meloidogyne spp., Radopholus similis and Hoplolaimus pararobustus. Pratylenchus goodeyi was the dominant species in all eco-regions except in Bugarama (lowland). Only the presence of P. goodeyi significantly correlated with root necroses. Altitude was strongly correlated with root densities of P. goodeyi and R. similis. A possible negative impact by P. goodeyi on banana yields was masked by the fact that nematode populations were positively correlated with high plant density and/or mulching practices, which led to relatively high plant vigour irrespective of soil type. Therefore, controlled field experiments will be needed to assess whether root necrosis caused by P. goodeyi at high altitude (>1400 m) actually has a detrimental impact on banana yields, similar to that observed for root-lesion nematodes at lower altitudes.