Reproductive fitness and pathogenicity of selected Radopholus populations on two banana cultivars

Ten populations of Radopholus similis from various locations and one population of Radopholus sp. from Indonesia were tested for their reproductive fitness and specific pathogenicity on Musa AAA, Cavendish cv. Poyo under controlled experimental conditions in a constant environment chamber. In addition, five of these populations were tested on Musa AAA, Ibota cv. Yangambi. Reproductive fitness of the populations tested on the two cultivars, measured as the ratio of the final number of nematodes per root system (P-f) to the number of nematodes inoculated (P-i), differed significantly. Greatest fitness was observed among R. similis populations collected from banana in different African countries (Cameroon, Uganda and the Ivory Coast) and one population from arecanut in Sri Lanka. In contrast, a population from tea in Sri Lanka and the population of Radopholus sp. from turmeric in Indonesia were the least fit. Specific pathogenicity was estimated at 8 weeks and 12 weeks after inoculation using three plant growth parameters: fresh root weight, fresh shoot weight and plant height, compared to uninfected control plants. Reduction in plant root weight was the best indicator of pathogenicity. While the R. similis populations from Uganda and the Ivory Coast were highly pathogenic, other populations with great reproductive fitness (i.e. isolates from Cameroon and Sri Lanka) did not significantly reduce root weight. In cv. Poyo, no linear correlation was found between final numbers of nematodes per gram of root (P-f) and the decrease of root weight.