Studies On The Mycorrhizal Fungi Of Three Species Of Rhododendron L.

Rhododendron is the congregation of Rhododendron L.plants,which is a branch of Ericaceae.Rhododendron is one of the most famous flowers in the world,ranked as one of China's top 10 famous flowers.Moreover,Rhododendron plays a role in pharmacy.The secondary metabolites of many plants in Rhododendron are the important sources of drugs and chemical raw materials.In addition,the wood of many Rhododendrons can be used for craft materials with beautiful colors and finer texture and the berries for food.Meanwhile,some of the Rhododendrons can purify air and improve the quality of environment.Thus,with the rapid development of the flower industry,the modernization of traditional Chinese medicine and environmental protection,the demand for Rhododendron plants also grows rapidly.Nevertheless,the Rhododendron plants are of shallow roots without the larger main ones.These roots are either thin or underdeveloped with few hairs and small seeds.In the natural state,the fungi, especially seedlings,can grow and develop normally,only when they form the symbiotic mycorrhiza correlating with Rhododendron plants.Therefore,the difficult growth of seedlings leads to the difficulties of artificial cultivation for Rhododendron plants.The proliferation of most Rhododendron plants(such as Rhododendron delavayi Franch.,Rhododendron irroratum Franch.,Rhododendron decorum Franch,etc.) relies mainly on ex-situ conservation,seed breeding,migration cuttings and seedlings breeding domestication.However,the rapid propagation is difficult for ex-situ conservation,long time needs for seed breeding,rooting cuttings is constrained by resources and seasons,and migration domestication is not beneficial for the protection of rare wild germplasm resources.At the same time,habitats of Rhododendron are threatened by human beings.Therefore,it is significant to study ericoid mycorrhizas.For Rhododendron plants(Rhododendron delavayi Franch.,Rhododendron irroratum Franch.,and Rhododendron decorum Franch.),this paper investigates the microstructures,isolation and cultivation,and strain identification of their ericoid mycorrhizas;their tissue cultivation of Rhododendron plants,and the growth-promoting of single and combined ericoid mycorrhizas reagents on their sterile and natural seedling plants.The combined surface disinfection method of 75%alcohol and 0.1%mercuric chloride was used to isolate these ericoid mycorrhizas.The disinfection duration lasted 1-10 min for mercuric chloride method,suitably 1-4 min.The ericoid mycorrhizas mainly distributed in the epidermal cells of roots.The experiments isolated 203 strains, wherein 72 strains for Rhododendron delavayi Franch.,74 for Rhododendron irroratum Franch.and 57 for Rhododendron decorum Franch.,respectively.Based on the preliminary morphological identification,these fungi belonged to Ascomycetes,Basidiomycetes and Deuteromycetes,of which Ascomycetes accounted for the vast majority,followed by Deuteromycetes and Basidiomycetes.Moreover,the preponderant fungi almost originated from the same Ascomycetes species.The results of tissue cultivation indicated that:as a basic medium,WPM medium was the more suitable for seed germination and shoot induction and proliferation;the hormone ratios of ZT 4.0 mg/L + NAA 0.2 mg/L and ZT 6.0 mg/L + NAA 0.05 mg/L were the more suitable for seed germination of Rhododendron delavayi Franch.and Rhododendron irroratum Franch.,respectively;while the hormone ratios of KT 4.0 mg/L + NAA 0.1 mg/L and ZT 4.0 mg/L + NAA 0.1 mg/L were suitable for shoot induction and proliferation of Rhododendron delavayi Franch.,and Rhododendron irroratum Franch,respectively.Additionally,the hormone ratios of ZT 4.0 mg/L + NAA 0.1 mg/L and ZT 6.0 mg/L + NAA 0.05 mg/L were respectively the most suitable for shoot induction and proliferation(proliferation rate of 66.7%) of Rhododendron decorum Franch.The growth-promoting of single(9 species) and combined(23 species) ericoid mycorrhizas reagents on the sterile and natural seedling plants showed that:Nos.27,28 and 29 single-reagents and No.4 combined-reagent were the most suitable for Rhododendron delavayi Franch.,followed by No.9 combined-reagent;while both Nos. 26,27,28 and 29 single-reagents and No.4 combined-reagent were most suitable for the natural seedlings of Rhododendron irroratum Franch.,followed by 6 and 7 combined-reagents,and 15 and 16 combined-reagents were lest suitable.