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The bio-protective effect of either single or dual mycorrhizal (AMF) and rhizobial colonisation of the roots of non-leguminous and leguminous banana intercrops differing in host response to Radopholus similis on the reproduction of this important migratory endoparasitic nematode was examined. Included in the study were sorgho-Sudan grass (good R. similis host), sweet potato and common bean (intermediate hosts), soybean and sunn hemp (poor hosts), and marigold (non-host). Significant plant growth-promoting effect of single AMF and rhizobial colonisation in the good and intermediate R. similis hosts sorgho-Sudangrass (AMF) and common bean (AMF and rhizobium), respectively, was observed whereas this plant growth-promoting effect was absent in the other intercrops with the exception of sunn hemp with significant plant growth-promoting effect of AMF colonisation on fresh root weight. An additive plant growth-promoting effect of dual AMF and rhizobial colonisation (on fresh shoot weight) was only observed in the poor R. similis host soybean. Single AMF and rhizobial colonisation also resulted in a significant bio-protective effect against R. similis in sorgho-Sudangrass (AMF), sweet potato cv. Inzovu (AMF) and common bean (AMF and rhizobium). The growth-promoting and bio-protective effects of AMF colonisation were clearly present in the good and intermediate R. similis hosts with moderate to high relative mycorrhizal dependency (RMD) values ranging from 47% (sorgho-Sudangrass) to 65% (common bean) but absent in the intermediate R. similis host sweet potato, which had a negative RMD value, and in the poor and non- R. similis hosts. Overall, no suppressive effect of R. similis infection on AMF and rhizobial colonisation was observed except in soybean and sunn hemp in which AMF colonisation was significantly reduced.

Summary The bio-protective effect of a root-nodulating strain (CNPAF 512) of the nitrogen-fixing rhizobium, Rhizobium etli, against both a sedentary (Meloidogyne incognita) and a migratory (Radopholus similis) endoparasitic nematode in common bean (Phaseolus vulgaris) was examined using an in vitro autotrophic tripartite culture system. Two in vitro assays were carried out with each of the nematode species. Each assay consisted of two treatments: the plants were either inoculated with the rhizobial strain or remained non-inoculated (control plants). To examine the effect of either pre- or simultaneous inoculation of the rhizobial strain on the reproduction of M. incognita and R. similis, one assay was carried out in which the nematodes were inoculated 3 weeks after rhizobial inoculation while another assay was carried out in which the nematodes were inoculated simultaneously with the rihizobial strain. Both pre-inoculation and simultaneous inoculation with R. etli CNPAF 512 significantly suppressed the reproduction of both M. incognita and R. similis.