Survey Of Alfalfa Disease In The Northeast Of China And Studies On Alfalfa Phoma Leaf Spot

With the development of alfalfa industry, the kinds of alfalfa diseases are increasing, it has become a major factor restricting the development of alfalfa industry.Through the field survey of alfalfa disease in the Northeast of China and identification of their pathogens, it is cleared that the kinds of these diseases and their damage degrees. In the survey, we found that the incidence of alfalfa Phoma leaf spot was serious and there had a strong potential danger. It is a devastating disease in the worldwide, causing yield decrease, quality deterioration and even can threaten the health of livestocks. In this paper, the pathogen identification of alfalfa Phoma leaf spot and its biological characteristics were studied to demonstrate the characteristics of pathogen; The evaluation of the resistance of alfalfa varieties to Phoma leaf spot were evaluated with 30 alfalfa materials collected from China and abroad at seedling stage, in order to provide a scientific basis for disease resistance breeding; The toxicity of ten kinds of fungicides were tested in the indoor and in the pot and field experiments so that effective fungicides could be selected from existing fungicides and provided scientific basis for alfalfa disease control. The main results are as follows:1. The field survey of alfalfa disease in the Northeast of China showed that the main diseases were alfalfa brown spot, alfalfa downy mildew, alfalfa Fusarium root rot,alfalfa rust, alfalfa Phoma leaf spot, alfalfa Stemphyllium leaf spot, alfalfa Leptosphaerulina leaf spot and alfalfa mosaic virus, respectively. The identification of pathogenic showed that 9 kinds of pathogens were pathogenic to alfalfa among these14 kinds of pathogens separated from the disease samples.2. The pathogen of the alfalfa Phoma leaf spot was identified with morphological and molecular biological methods, and the effects of temperature, medium, p H,illumination, humidity and the sources of carbon and nitrogen on the pathogen were studied. The result showed that the pathogen was identified as Phoma medicaginis.The optimal temperature for mycelium growth, sporulation and spore germination were 20, 20 and 25 ℃, respectively; the suitable media were V8, alfalfa leaf juicemedium and dextrose peptone, illumination was conductive to mycelium growth and sporulation, while the difference of spore germination between different illumination treatment were not obvious; the suitable carbon sources were sucrose, glucose and fructose, respectively; And the optimal nitrogen sources were meatext, peptone and yeast extract, respectively; The spore germination need higher humidity, they can germinate best in the water drop, while it can not germinate under RH 85%. The lethal temperature of mycelium was 50 ℃(10 min) and the lethal temperature of conidia was 44 ℃(10 min).3. The evaluation of resistance was conducted with 30 alfalfa materials(cultivars)collected from China and abroad at seedling stage and activities of phenylalanine ammonia lyase(PAL), catalase(CAT) and superoxide dismutase(SOD) were also studied by using ultraviolet spectrophotometer colorimetic method. The results showed that the resistances of different materials had marked differences against the alfalfa Phoma leaf spot, the disease indexes of 30 materials were ranging from 4.28 to51.65, of which Medicaginis sativa Aohan come from Inner Mongolia was highly resistant and M. sativa Shanxi come from Shanxi was highly susceptible, 10 cultivars were moderate resistant. The test of CAT and SOD activities showed significant differences among each materials before inoculation(P<0.05), while PAL activities were not. The activities of three enzymes were increased after artificial inoculated with Phoma medicaginis, CAT and PAL activities were first increased then decreased,SOD activities showed a descending trend. These enzymes activities had significantly different among the same material at 4th, 8th, 12 th days after inoculation(P<0.05).4. In order to screen effective fungicides to control alfalfa Phoma leaf spot, the toxicity measurement against its pathogen by using mycelia growth rate method and potted experiment, field efficacy trial were carried out. The results of toxicity measurement showed that the inhibition rate increased with the concentration in the same fungicide, of which the inhibition action of 96% Propiconazol was highest and its EC50(0.5690 μg/m L) was lowest. The results of potted experiment showed that the efficacy of 96% Propiconazol was best and the EC50 was 4.778 μg/m L. All thecomplex formulation showed synergistic effect, except for five combination for additive effect, there was no antagonistic effect. The results of field efficacy trial showed that the efficacy of Propiconazol was best at the same concentration among the single dosages and its efficacy was 78.18% when the effective dose was 250g/hm2. The synergismtic effect of Propiconazol mixed with Mancozeb was the most obvious among the mixtures when their effective doses were 1:1.