Attractancy of bacterivorous nematodes to root-adhering soils differs according to rice cultivars

We tested the ability of root-adhering soils (RAS) from eight rice cultivars to attract a bacterivorous nematode (Acrobeloides sp.) living in a poor-nutrient soil in Madagascar. We showed that the ability of rice to attract bacterivorous nematodes in its rhizosphere is variable among cultivars. FOFIFA 172 was the cultivar with the highest attraction value, the lowest root biomass (RB) and the highest RAS:RB ratio and RAS respiration. In contrast, nematodes exhibited strong repellent response to W880 RAS. Also, nematode attractancy was not related to rice resistance against pests (blast rice disease and Striga asiatica) neither to cultivar ability to grow at specific altitude. Our results suggest a trade-off in carbon allocation between plant biomass and root exudation driving nematode attractancy and raise questions about the impact of plant breeding on cultivar ability to interact with soil mutualists such as bacterivorous nematodes. Further investigations are required into (i) variation in root exudate quantity and composition among the eight cultivars and (ii) the response of rice cultivars to bacterivorous nematode inoculation.