Reproduction of natural and selected resistance-breaking Meloidogyne populations on near-isogenic tomato lines
AbstractThe near-isogenic tomato cultivars Motelle (bearing the Mi-gene for resistance to Meloidogyne spp.) and Moneymaker (susceptible) were inoculated with 16 Meloidogyne populations. An average reproduction index for each population was obtained from a series of inoculations carried out over a period of three years. Most of the populations were able to break the resistance and to reproduce successfully on the cv. Motelle. Resistance-breaking populations came directly from fields in different countries (naturally virulent populations) or were selected under greenhouse conditions by repeated inoculations on resistant tomatoes. Naturally virulent populations from North Africa showed the greatest degree of reproduction on resistant tomato, whilst other tropical and Mediterranean populations had lower rates of reproduction, but still comparable with that of the populations generated by selection. Generally, a given population reproduced better on the susceptible than on the resistant isoline. The resistance-breaking ability of Meloidogyne populations has been found to be durable on resistant tomato over many years; moreover, populations retained their virulence even if reproduced for several generations on susceptible plants.