Differential response in growth and mycorrhizal colonisation of soybean to inoculation with two isolates of Glomus clarum in soils of different P availability

Abstract

Soybean (Glycine max cv. Mikiwashima) seedlings were inoculated with two tropical isolates of the vesicular-arbuscular mycorrhizal fungus Glomus clarum (Gc); isolate GcA was isolated from soils of low phosphate (P) and isolate GcB from soils of high P availability. In soil with low P, GcA was more efficient in increasing growth, nodulation and nitrogenase activity of G. max than GcB. Upon contact with the root surface, pre-infection hyphae of GcA penetrated the root directly and rapidly colonised the cortical cells, while those of GcB grew extensively on theroot surface with little host penetration. Mycorrhizal colonisation was higher in roots inoculated with GcA. Dual inoculation with the two isolates did not increase the effect of the single inoculation with GcA. In soils of high P status, both isolates formed pre-infection hyphae with few entry ooints and percentage mycorrhizal root colonisation was consequently low. The variation in efficacy of the isolates emphasizes the significance of evaluating host specificity when selecting efficient VA mycorrhizae strains for field studies. © 1988 Kluwer Academic Publishers.