Potential of Crotalaria species as green manure crops for the management of pathogenic nematodes and beneficial mycorrhizal fungi

On the basis of preliminary experiments, some Crotalaria species from Senegal were investigated to determine (1) their susceptibility to Meloidogyne javanica and M. incognita compared to a sensitive host (tomato), (2) their mycorrhizal and rhizobial responses, and (3) the effect of their cultivation on the mycorrhizal soil infectivity. The nematode invasion rates on Crotalaria spp. ranked from 0.17 to 7.17% and from 0.58 to 5.25%, respectively, for M. incognita and M. javanica, vs. 97% and 77% on tomato. Moreover, the inoculated J2 which invaded tomatoes developed into adult females, while those on Crotalaria spp. rarely developed beyond the third stage, confirming that all Crotalaria spp. evaluated are non hosts or poor hosts. In two other experiments, Crotalaria spp. were inoculated with an arbuscular mycorrhizal fungus (Glomus intraradices). Mycorrhization was generally well developed among Crotalaria species, and mycorrhizal colonization enhanced mainly phosphorus content of shoot tissues and always significant plant growth. Inoculation with both rhizobial isolates and Glomus intraradices enhanced growth and nodule formation on some Crotalaria species. The data recorded in both experiments showed, for the first time, that Crotalaria spp. are highly mycorrhiza dependent, some of them reaching more than 90% mycorrhizal dependency. Among Crotalaria species, twelve were used in two different experiments. A significant correlation was obtained between their mycorrhizal dependencies calculated on the shoot dry mass recorded in each experiment. Crotalaria spp. could be used as pre-crops for providing green manure while at the same time decreasing the level of detrimental nematodes and increasing the level of beneficial mycorrhizal fungi.