Evaluation of the ability of soil microorganisms and mycorrhizal fungi to promote rooting and development of Gnetum spp. cuttings

Abstract

Experiments were conducted to investigate the role of soil microorganisms from diverse Land Use Systems (LUS) on Gnetum rooting from Okola and Nkoteng sites (humid forest, Cameroon). Gnetum-mycorrhizal fungi symbiosis (Ecto and Arbuscular mycorrhizal fungi (EMF and AMF) is considered for the production of quality seedlings. The cuttings were planted using a factorial randomized design with sterilized and unsterilized substrates x LUS (mixed crop field: MCF, fallow: FA and secondary forest: SF); after sieving and autoclaving. The seedlings received AMF, AMF + Sm, Sm (soil mixture) inoculum. The results indicate that soil sterilization reduce organic matter and phosphorus, plant growth and rooting; increase cutting mortality. The activity of CMA (infective propagules/g soil) is more important in MCF (12-35) than FA (0.4-1.4) and SF (0.16-0.40). This is confirmed by Scleroderma colonisation on Gnetum roots which is higher in MCF (54-66%), medium in FA (34-54%) and low in SF (15-33%). Selected AMF inoculation increase Gnetum size (response: 60-67% un-sterilized, 71-85% sterilized substrate and 35-59% soil mixture) when compared to the non-inoculated control cuttings (20-30%). Introducing AMF and EMF in the rooting medium may improve Gnetum cuttings quality. The work suggest that Gnetum can benefit from the double EMF and AMF symbiosis.

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Keywords: Mycorrhizal fungi, double symbiosis (arbuscular, ecto-mycorrhiza), Gnetum spp., Scleroderma sp.