Pathogenicity Of Rhizoctonia Solani To Alfalfa And Disease Resistance Of Alfalfa Varieties

Alfalfa(Medicago sativa)is the most widely planted and high-quality legume forage in China and the world.Rhizoctonia solani root rot is one of the major constraints in alfalfa production,which influences the yield and quality of this pature,resulting in the decay of grassland.R.solani is one of the important pathogens of alfalfa root rot,which can survive in soil and plant for long preiod,it is particularly difficult to control root rot of alfalfa.At present,studies on the pathogenicity of R.solani and disease resistance of alfalfa varieties are relatively weak.In this paper,the pathogens were isolated from the root samples of different alfalfa planting areas in Gansu Province,and then evaluated the pathogenicity of representative R.solani strains to alfalfa by soil inoculation method.Finally,disease resistance of alfalfa varieties at home and abroad to R.solani root rot was studied.To provide theoretical basis for the effective control of R.solani root rot of alfalfa.The main findings are as follows:1.In 2017 and 2018,116 root rot plants were collected from Anding and Lintao of Dingxi,Loess plateau grassland agricultural system test station of Qingyang,Huanxian of Qingyang,Yongchang of Jinchang,Minle of Zhangye,Linze of Zhangye and Liangzhou of Wuwei,pathogenic isolates were obtained by root tissue isolation method and were identified based on morphological characteristics and gene sequencing analysis,188 isolates of R.solani accounted for 18.99% of the total isolates,R.solani isolated from Liangzhou of Wuwei accounted for 32.88% of the total isolates from the site,followed by Minle and Yongchang,accounting for 25.97% and 18.60% of the total isolates from each site.R.solani isolates accounting for 11.88% from Huanxian,and no R.solani isolates from Linze.2.17 R.solani isolates were inoculated into 2 alfalfa varieties by soil inoculation method.The root and crown disease index,plant height and root length,aboveground and underground biomass were measured to evaluate the pathogenicity of different R.solani isolates to alfalfa varieties.The results showed that the pathogenicity of 17 isolates of R.solani to alfalfa were significant difference(P<0.05).Root and crown disease index of Longdong no.3 inoculated with different isolates were both between 10.00 and 100.00,the relative reduction of plant height and root length were between 25.42% and 100.00%,0.14% and 100.00% respectively,relative reduction of aboveground and underground biomass were between 11.43% and 100.00%,11.01% and 100.00% respectively.Root and crown disease index of Zhongmu no.1 alfalfa inoculated with different isolates were between 6.00 and 88.00,6.00 and 85.00,the relative reduction of plant height and root length were between 4.53% and 82.52%,13.45% and 84.24% respectively,relative reduction of aboveground and underground biomass were between 10.64% and 85.37%,27.30% and 88.95% respectively.The pathogenicity of different alfalfa varieties inoculated with the same isolate was different.In summary,the more pathogenic isolates are R4、R5、R6、R15 and R18,and the less pathogenic strains are R14、R16、R19、R20 and R21.3.77 alfalfa varieties were inoculated with the R.solani strain R10 by soil inoculation method,and root disease index,plant height and root length,and aboveground and underground biomass were measured to evaluate disease resistance of alfalfa varieties.The results showed that the disease resistance of different alfalfa varieties to R.solani was different.A cluster analysis of alfalfa varieties was based on all indicators,77 alfalfa varieties were divided into three types including susceptible(S),moderately resistant(MR)and resistant(R).Among them,the S type contained 43 varieties,accounting for 56% of the total tested varieties,such as Aurora,"030",Gannong no.6,Baoding alfalfa,common alfalfa and WL366HQ;the MR type contained 27 varieties,accounting for 35% of the total tested varieties,such as Gannong no.9,Huaiyang 4,"020",Salt tolerant star,Zhongmu 1 and Victoria;the R type contained 7 varieties,accounting for 9% of the total tested varieties,Gannong no.7,Hunter Field,Arc,UC-1465,WL316,4020 and 4030.The relative reduction of plant height,root length,and aboveground and underground biomass of disease resistant varieties were significantly lower than those of susceptible varieties.