Studies On Etiology And Control Of Alfalfa Anthracnose

Alfalfa anthracnose caused by Colletotrichum spp is a destructive disease in alfalfa growing areas. As early as in 1947, the disease was reported in the Southern United States, after then many countries of the world have been reported. The first report of alfalfa anthracnose caused by Colletotrichum trifolii on Medicago falcate in China. It was been in northwest, northeast and northern China in 50 s. In recent years, the research group of alfalfa diseases have investigated that alfalfa anthracnose incidence increases yearly and harmful aggravated. The average infection rate up to 42.3% and the highest infection rate up to 70% of alfalfa caused by C. spp, which can cause the yield losses up to 10.1% ~ 54.4%. Therefore, the aim of this study was to obtain the pathogen from the tissues with anthracnose and identify pathogen species constitution based on morphological characters and multilocus(ITS、ACT、CHS-1 and GADPH) sequences phylogenetic analysis. The resistance to C. linicola=C. lini in seedling stage of 50 alfalfa germplasm resources was evaluated by the method of pot experiment. Then the 10 fungicides were tested to control alfalfa anthracnose(C. linicola=C. lini), in order to provide the basis for the control methods of those diseases in China. This study mainly results were as follows:1. The 9 Colletotrichum spp isolates obtained from northeast and north area of China was characterized with morphology and multi-gene( ITS、ACT、CHS-1 and GADPH) sequences phylogenetic analysis. The results showed that C. linicola, C. truncatum, C. spaethianum were associated with alfafal anthracnose in China. C. spaethianum is first report as associated with alfalfa anthracnose. C. linicola is reported for the first time associated with alfalfa in China.Pathogenicity testing showed that all species can infect alfalfa causing anthracnose. C. linicola(Strain JL01, NM05) was virulent on alfalfa seedlings. incidence rates get in between 43% and 39%. Secondly, C. truncatum(Strain HB06, HB08, HB09) infected experimental seedlings. The pathogenicity of C. spaethianum(strains HB07, JL02, JL03 and NM04) was weak, and the incidence rate was less than 24% after inoculation for 14 d.2. The resistance to anthracnose in seedling stage of 50 alfalfa germplasm resources was evaluated by the method of pot experiment. The indexes were measured, such as index of disease, plant height, biomass, relative plasma membrane permeability, proline content, soluble sugar content and lignin content. The resistance evaluation was carried out directly by the index of disease index. The evaluation results of disease index showed that these were high resistance, including: Rangelandor, Drylander, Hulunbeier, Tulufan, Honeoye, Algonquin, Tumu No.1, Dupuits and Seguel. They were high susceptibility, such as Xinjiang Daye, Faguo(M 7), Yuci, ‘M 6’, Cangzhou and Pramar. Furthermore, the main index of 4 with resistance identification of alfalfa was selected by principal component analysis. Subordinate function analysis showed that Rangelandor, Honeoye, Algonquin, Tumu No.1, Aohan, Tulufan and Seguel were strong resistance of materials. However, Faguo(M 47), Rembler, Wugong, Caoyuan No.3, Longdong, Xinjiang Daye, Longzhong, Pramar, Cangzhou and Yuci were susceptible of materials. The combination of the above two kinds of method to determine the resistance to anthracnose in alfalfa seedling strong germplasm: Rangelandor, Honeoye, Algonquin, Tumu No.1, Tulufan and Seguel; While Yuci, Cangzhou, Pramar, Xinjiang Daye and Faguo(M 47) were susceptible to anthracnose.3. Laboratory toxicity of ten fungicides to this pathogen was tested, control efficacy in pot and field were determined. The results showed that 98% pyraclostrobin, 98.1% carbendazim, 97.7% prochloraz and 98% azoxystrobin had better inhibiting effects on the mycelium growth of C. linicola, EC50 were all less than 1 mg/L. The toxicity of 98% pyraclostrobin was the highest, EC50 was 0.2077 mg/L. The results in pot experiments showed that 98% pyraclostrobin was the best for controlling this pathogen, EC50 was11.0757 mg/L; among the 12 kinds mixtures only one had additive effect, other mixtures showed synergistic effect. The field control efficacy of 25% pyraclostrobin(150 g/hm2), mixture of 25% prochloraz(150 g/hm2) and 50% carbendazim(300 g/hm2), 50% carbendazim(300 g/hm2) were the best, with 78.87%, 73.86% and 67.85%, and the yields of alfalfa were increased by 58.70%, 59.42% and 51.14% respectively. Considering factors of control effects and yield, 25% pyraclostrobin, 50% carbendazim, 25% compound prochloraz and 50% carbendazim were effective fungicides to alfalfa anthracnose caused by C. linicola.