Identification Of Fusarium Root Rot Pathogens And Evaluation Of Alfalfa(Medicago Sativa L.) Fusarium Root Rot-Resistant Germplasm Materials

Alfalfa(Medicago sativa L.)is one of the most important forage in the world.As a herbaceous perennial leguminous plant,Alfalfa has stout taproot,developed roots and strong resistant to drought and cold,in addition,strong regeneration.Root rot is an important root soil borne disease worldwide which can be harm to alfalfa in each growing period.When root rot occurs,taproot decay happens.With the aggravation of the disease,the decay progresses develop to the root crown,causing the leaves to turn yellow and fall off until death.The pathogens of fusarium root rot of alfalfa have been reported in China,mainly including Fusarium oxysporum and Fusarium solani,etc.However,the pathogenic fusarium causing root rot of alfalfa in different regions are various.In order to explore the pathogens and pathogenicity of alfalfa root rot in other unreported areas in China and to screen the germplasm materials with different resistances,the germplasm materials were used for genetic diversity analysis and disease resistance breeding of alfalfa.In this study,we collected root rot disease samples of alfalfa from Wuhai,Inner Mongolia in 2018,to determine the dominant pathogens of alfalfa in these places.Pathogens were isolated from the samples and purified on PSA and other media.We identified the pathogens by observing the colony morphology,color,mycelia and conidia in size,and then amplified and sequenced ITS and TEF-1? sequences of the fungi.Morphological and molecular biological methods were used to identify the representative pathogens and then determined pathogenicity by back infestation test.According to the results,a total of 4 strains were isolated and identified,respectively named 22,28,17-2,50.Strain 22 was Fusarium acuminatum,strain 28 was F.oxysporum,strain 17-2 was Fusarium equiseti and strain 50 was F.solani.Among them,strain 28 was most pathogenic and the morbidity was close to 100%?Then strain 28 were used to infect 83 alfalfa germplasm materials from different countries and regions to evaluate their disease resistance.In this study,the pathogen was inoculated by hydroponics.Plant height,root length and underground biomass were measured and the disease index was calculated after 14 days.The results showed that the resistance of 83 alfalfa germplasm materials to root rot disease was significantly different.The disease index ranged from 12.5 to 70.83.According to the disease index,four different levels of resistance were divided,which were disease-resistant materials,disease-tolerant materials,disease-susceptible materials and high-sensitive materials.According to the clustering results,83 alfalfa materials can be roughly divided into 3 categories: 39 resistant materials,23 susceptible materials and 21 susceptible materials.Although part of the materials are not completely consistent with the disease index classification results,but resistant materials and the susceptible materials can be clearly distinguished in clustering analysis results.Although we used different analysis method,PAMPA and No.1377 were classified as resistant material and G13608,Pianguan,Yanggao,Aohan,Langshan,Gannong No.3,Beijiang,CF030056,XinmuNo.2,Longmu No.1,a total of 10 germplasm materials,were high-sensitivity materials.