Pathogenicity Test On 15 Fungal Species Isolated From Alfalfa Roots

Alfalfa root rot is one of the key factors limiting production.There are more than 100 species pathogens in abroad,while in China only found were less than 10 species such as Fusarium,Rhizoctonia.In order to determine our country?s pathogens of alfalfa root ro in China so that late management and further research,the pathogenicity of 15 species(25 isolates)fungi isolated from alfalfa roots were tested in greenhouse in this thesis.Prior to do this work,a problem occurred during alfalfa culture in greenhouse will be resolved by optimizing nutrition and water supply.The main results are as follows:1.Among tested fungal species,there were 12 species pathogenic to alfalfa.There were Coltetotrichum destructivum,C.0 trifolii,C.americae-borealis,Rhizoctonia solani,Phoma medicaginis,Paraphoma radicina,Phoma sp.,Fusarium oxysporum,F.Sonali,F.equiseti,F.proliferatum and F.tricinctum.In which,3 species in Coltetotrichum genes and 2 species in Phoma genus were first report in the world.Paraphoma chrysanthemicola and Verticillium alfalfae already known were alfalfa pathogen,whereas,no symptoms presented in this test.2 The pathogenity from high to low were as Coltetotrichum destructivum,C.trifolii,C.americae-borealis,Rhizoctonia solani and F.proliferatum.All caused plant death,the mortality in 8 wk is 68.40%,10.53%,10.00%,5.30% and 5.00%.Others did induced death,only discoloration presented on root surface.Root length,root diameter,root surface area,and root dry weight of plants inoculated the 12 pathogenic fungi decreased 8.4%-56.8%,11.4%-45.7%,30.7%-77.2%,50%-89%.3 The optimized condition for culturing healthy alfalfa plants in the greenhouse is irrigated Scotts plant nutrient solution,12 h 6680 LUX light using LED plant light at 22°C,and then 12 h dark at 18°C,and soil were sterilized.Leaves were green,and no one leaf blade turned to yellow or defoliated under supplied the Scotts solution,while some leaves are not healthy under supplied with Hoagland's nutrient solution,tap water and distilled w ater.Compared with tap water,plant height,fresh weight,shoot dry weight,root fresh weight,root dry weight,root area,root dimeter,number of leaves,and stem node number all increased,respectively increaed 256%,731%,655%,384%,445%,101%,27%,84% and 112%,significantly higher(P<0.05).