Effects of extraradical mycelium network of an arbuscular mycorrhizal fungus on the growth of banana plantlets.

Actively growing extraradical mycelium extending from mycorrhizal plants is an important source of inoculum in soils. We investigated the ex vitro mycorrhization of banana plantlets through a pre-established extraradical mycelium (ERM) network arising from maize plants. In the first part of this study we evaluated the efficiency of banana root colonization in the ERM network (the network inoculation (NI)) by comparing with the classical inoculation (CI) (spores and colonized roots placed in the planting hole of the plant). In the second part of this study we evaluated the plant growth response to these types of inoculation. The results showed that the plants in the NI treatment were heavily colonized three weeks after inoculation (87.3 %) and produced a high amount of arbuscules (60.9 %) and vesicles (28 %). In the CI treatment, these values were 64.7 %, 44 % and 18.5 % for hyphae, arbuscules and vesicles respectively. Ten weeks after the transfer of the plantlets to individual pots (at the end of the second part of the experiment), the percentage of hyphae and arbuscules was still significantly (P<0.05) higher in the NI treatment than in the CI treatment. The growth parameters showed similar trends in NI plants compared to CI plant. The accumulation of dry matter increased at 90% and 53% respectively for NI and CI treatments in comparison with NM treatment. These results support the conclusion that ERM network may improve the practical exploitation of native arbuscular mycorrhizal fungi (AMF) under banana cropping systems.