Mycorrhizal status of 'Gnetum' spp. in Cameroon : evaluating diversity with a view to ameliorating domestication efforts
In the current study the diversity of ectomycorrhizal fungi associated with Gnetum spp. in Cameroon was investigated. The physiology of the most predominant endophyte in pure culture was evaluated. The possible effects of ectomycorrhizal infection on the plants growth was investigated by comparing growth of mycorrhizal to non-mycorrhizal plants. Gnetum spp. were found to be ectomycorrhizal in all sites visited during the survey. There were just two ectomycorrhiza morphotypes (‘yellow’ and ‘white’) associated with this plant such low diversity is unusual for an ectomycorrhizal plant host. The yellow morphotype was the most widespread and prevalent and was identified as Scleroderma sinnamariense. Mycelia were isolated from sterile ectomycorrhizal root tips. S. sinnamariense in pure culture was capable of growing on organic nitrogen sources. Growth was also recorded in the presence of some sparingly soluble P sources like hydroxyapatite, calcium hydrogen phosphate, phytate and iron phosphate. The fungus expressed acid phosphatase activity and showed a capability of solubilising sparingly soluble calcium hydrogen phosphate. Mycorrhization led to an increase in growth of the plant. A linear relationship between ectomycorrhizal colonisation was observed with total foliar nitrogen but not with phosphorus. There is a functional relationship between ectomycorrhizal colonisation and nutrient uptake but improvement in growth may not be exclusively as a result of increase P uptake. Our data indicates that mycorrhization and fertilisation would be needed for Gnetum growth and establishment in plantations. It is also necessary that the type and amount of fertiliser be chosen carefully so as to avoid any adverse effect on the ectomycorrhizal infection.