Development and Evaluation of a Standard Method for Screening for Resistance to Radopholus similis in Bananas

The description and evaluation of a standard assay method for screening for resistance of bananas to the burrowing nematode (Radopholus similis) under greenhouse conditions is presented. Seven banana genotypes, ranging from susceptible to resistant, were used to evaluate the method. Banana plants from tissue culture, grown in 0.4-liter Styrofoam cups containing sterilized sand as substrate, were maintained in the greenhouse for 4 weeks before inoculation. Two hundred burrowing nematodes, reared in monoxenic carrot-disk culture, were used as inoculum for each container. Plants were kept in the greenhouse for an additional 8 weeks at about 27°C and 80% relative humidity after inoculation. Burrowing nematodes reproduced well in the susceptible cultivars False Horn, Grande Naine, Valery, and Lacatan, whereas the reproductive fitness was very low in the resistant cultivars Pisang Jari Buaya and Yangambi. An intermediate reaction between these two groups was observed with Pisang mas. A similar trend was obtained in a follow-up field test, which indicated that the method is accurate and reliable. Assessments of total-root necrosis associated with this pathogen were also comparable between greenhouse and field conditions. However, nematode effects on the roots were more severe in the greenhouse test than in the field. In spite of low nematode reproductive fitness, root necrosis was relatively high in the two resistant cultivars tested in the greenhouse trial.