Study On Pathogen Of Alfalfa Root Rot In Gansu Province

Alfalfa root rot is a general term for a group of pathogens locally infecting crowns, or taproot,lateral roots, root hairs, and caused discoloration or root of diseased tissues, plant declination even death, plant density decrease annually until decline completely, yield and quality also effecdted greatly. Fusarium spp. confirmed were the causal agent of alfalfa root rot in China. However,other pathogens were less recorded on the plant. Therefore, species of its pathogens were less than recorded in other countries. In order to determine if there are new pathogens in the world or in China, causal agent and significance was studied by investigeation in Gansu Province which has the largest alfalfa planting area in the country, isolation, culture and identification morphologically and molecularly in this thesis so that mange the key diseases. The main results obtained are as follows:1. Occurrence of alfalfa root rot were investigated in Yongdeng county, Yuzhong county,Huining county and Ganzhou district in Zhangye city. There are 78 varieties in the former two counties, respectively 40 and 48(14 varieties were same). There are 3 varieties in later two counties. Based on the growth in field, some plants in Yuzhong and Ganzhou exhibited symptoms similar to root rot such as leaf yollowing, shoot dwarf or wilt and plant death. There was no such symptoms appeared in other two places. In contrast, decloration and rot appeared on most plant roots in all sites, especilly, this pathogenic changes increased by the years increased in Huining county.2. There were 11 species of fungi isolated from symptomatic or asymptomatic plant roots collected from all study sites, in which 4 species were Fusarium(Fusarium acuminatum, F.oxysporum f. sp. ciceris, F. solani and F. tricinctum), 2 species of Paraphoma(P. radicina and Paraphoma sp.), Phoma medicaginis var. medicaginis, Clonostachys rosea, Myrothecium sp.,Helminthosporium solani, Plectosphaerella cucumerina. Totally, there were 3, 3, 5 and 7 species in Yongdeng, Yuzhong, Huining and Ganzhou, dominant species respectively were Fusarium acuminatum, Myrothecium sp., Helminthosporium solani and Paraphoma radicina.3.Among the 11 fungal species,8 species was pathogenic to alfalfa result from pathogenicity test with the method of dipping inoculation on 3-day seedlings,cultured in greenhouse,harvested after 8 week,and evaluated incidence and index according to symptoms on roots.The virulence(Pseudomonas viridiflava)、Aplanobacter insidiosum、密执安棍状杆菌(Clavibacter michiganensis subsp.Insidiosus)(Jones and Mc Culloch,1926;Jones,1925;Heydari et主要由燕麦镰孢(F.avenaceum)、尖镰孢(F.oxysporum)、腐皮镰孢(F.solani)引from strong to weak was Paraphoma sp.(incidence was 82.22%,index was 54.86),F.solani(91.67%,34.58),Helminthosporium solani(52.59%,23.33),F.acuminatum(71.67%,20.00),Paraphoma radicina(82.22%,54.86),P.medicaginis(66.67%,15.00),F.oxysporum(33.33%,15.00),F.tricinctum(33.33%,8.33).This study firstly found that Paraphoma spp. and Helminthosporium solani were the pathogens of alfalfa root rot in the world. In China, Phoma medicaginis also caused alfalfa root rot beside leaf spot and stem black proviously reported.