Evaluation of the ability of soil microorganisms and mycorrhizal fungi to promote rooting and development of <i>Gnetum</i> 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.