Studies On The Fungi Related With Panax Quinquefolium L. Root Rot In Beijing

American ginseng (Panax quinquefolium L.) is a medicinal crop which provides millions of dollars in income every year for Chinese farmers. Most of the ginseng are planted at a very high density, and high planting densities are related to high disease levels. Therefore root rot is a serious problem in ginseng plantation.Another serious problem which obstacles the development of the industry of ginseng is the replant problem. Owing to the fact that Ginseng and Quinguefolium connot be continuously cropped on the same land and the contradiction between Ginseng industry and forest industry is increasingly sharpening. And the root disease become very seriously at most ginseng garden. But there is no effective methods solving this problem.The author of this article propose to find the pathogen of root rot disease of panax Quinguefolium L. in Beijing, then study the relationship between the pathogen and allelochemicals. There are two objectives, one is to try to find the main reasons for replant problem; the other is to release this problem by means of different treatments on the continuously cropped ginseng soil , and analysis the population dynamics of the soil fungi as well in order to find whether the pathogenic fungi have some relations with the seedling survival rate of Panax quinquefolium L. .1. Isolation and identification of fungus strains related with American ginseng root disease and pathogenicity of some isolatesOne hundred and eight fungi were isolated from the roots of diseased Panax Quinguefolium in 9 American ginseng gardens in Beijing or Jilin, China. Fusarium sp. was the major species. Experiments of pathogenicities were performed in 27 strains of high-frequency by the Koch's postulates. Eight pathogenic fungi were documented, and Strain F19 was highly virulent. Four strains of Fusarium solani were studied in biological characters. Crude culture filtrates of strains TF1 and F19 had strong toxcity against leaves and radicals of American ginseng by bioassay methods.2. Identification of fungi species related with American ginseng root diseaseTweenty strains of high-frequency were identified by morphology and molecular method, including 13 species of 7 genuses. And Fusarium sp. was the major species.3. Effects of allelochemicals on main pathogenic fungi of American ginsengThe relationship between American ginseng root exudates and its main pathogens was studied. The root exudates can promote the number of propagula of the pathogenic fungi in high concentrations. Then we studied the interactions between the allelochemicals, phenolic acid compounds and the main pathogenic fungi by pot test and found that phenolic acid could inhibit the growth Phytophthora cactorum but increased the index of disease of Fusarium solani.4. Studies on the impact of organic additives on the replant American ginseng and the soil fungiFirst, we analysised the fungi community of healthy or unhealthy soil samples from 3 different places by selective medium. The number of soil fungi in healthy soils is more than in unhealthy soils; the number of Fusarium sp. have no regularity; but the number of Phytophthora sp. in healthy soils are less than in unhealthy soils. To compare the effect of different organic amends treated replant soil and to find the relations between the soil fungi community and the growth of Panax quinquefolium L. seedling, soil was treated with bone meal and Perilla frutescens root meal in the replant ginseng garden; the rate of seedling emergence, incidence of root rot and root weight were investigated; the fungi community and the pathogen Fusarium sp. and Phytophthora sp. population were counted by soil dilution plating technique. The organic amendments especially treated soil could reduce the population of Fusarium sp. and Phytophthora sp. in soil, thus lessen the root disease of continuous cropping and increase survival of seedlings.