Identification And Biological Characteristic Analysis Of Pathogen Causing Gray Leaf Spot Of Tomato

Tomato is one of the most widely grown vegetables in the world. The popularity oftomato among consumers has made it an important source of vitamins A and C in diets.However, tomato gray leaf spot is becoming more and more serious in our country withmore imported cultivars planted. The disease is a kind of foliar disease, which initialsymptoms were leaf spots with 2 to 4 mm in diameter, irregular circular, and gray-green incolor. These develop white to gray centers surrounded by a red to brown margin. Lesionsmay be numerous causing leaves to turn yellow, then brown and drop. Tomato willdefoliate when this disease have happened severity in the filed, which may effect thecharacter of fruit. Beril is a variety with high yield and beautiful fruit, good rigidity, stronganti-rending and longer storing characters, bred in the Holand. In order to know theresistance of the tested varieties to tomato gray leaf spot very well, the disease index andthe frequency of disease leaf were analyzed on the basis of the some symptoms of damagewere described in the field from April to November in 2006. The pathogen causing thetomato gray leaf spot has been reported caused by different pathogens in the home andabroad.In this study, three pathogens causing the disease were determined by Koch'sPostulate in greenhouse. With the biology characters of the pathogen, the effectivefungicides were screened. The main results were shown as follows.1. According to the invested data about the damage occurrence of tomato gray leafspot from April to November in 2006, the damage period and character were determined inthe Beril variety. The relative humidity was the key factor which affects the developmentof gray leaf spot of tomato during a growth period, in particular, which can be improved bythe rainfall or the flooding in the agricultural management, was beneficial to thedevelopment of disease and transmission of pathogen. But temperature and light were notimportant factors. The character of occurrence was defined that the disease at the bottomwas more severe than that in the middle and top of the plant, the disease in the middle ofthe plant was more severe than top in the damage leaf, and the disease leaves weredistributed from blow to top on the whole plant.2. The separate method of fungi lied to the general one. According to the morphologi- cal characteristic and size of acervulus, condiophore and chlamydodpore, one of thepathogens was identified as S. solani. The other two pathogens were still need to beidentified clearly in the future.3. The biology characters of pathogens were researched at different the temperature,pH, light volume period, different culture medium, different carbon source and nitrogensource. For the mycelial growth of S. solani, the optimum temperature was 25℃～30℃,the range of pH value was very wide, and the treatment of light was continuing. Thepathogen can grow at high ratio in the Czapek and Oat culture medium. The maltose,glucose and solubility amylum were taken advantage as the carbon source. However, thenitrogen source has inhibition to the growth of S. solani. For the mycelial growth ofpathogenⅡ, the optimum temperature was 20℃～25℃, the range of pH value was 4～6and 8～11, but the middle pH was not suitable to the growth of pathogenⅡ. Either thecontinuing light or the darkness has not significant effect on the mycelial growth. Therewas high growth ratio on the Oat and PSA culture medium. The other carbon source exceptthe maltose was utilized. But, the carbamide has strong growth-inhibition-ratio as thenitrogen source. For the mycelial growth of pathogenⅢ, the optimum temperature was 25℃～30℃, the range of pH value was 7～8 and the treatment of light were alternate lightand darkness. It has high growth ratio on the Czapek and tomato seedling juice culturemedium. The carbon source included maltose, lactose, glucose, sucrose and solubilityamylum were not utilized well. However, the nitrogen source included ammonium sulphateand ammonium chloride have inhibition to the growth of pathogenⅢ.4. Six fungicides were screened for their toxicity to main pathogens of the disease inlaboratory with growth rate method. The Dupont flusilazole which have good restrainingeffect to three pathogens, the inhibition ratio was up to 66.67%,56.36%,81.63%,respectively. Although the Amistar has not strong inhibition to the S. solani, it has highinhibition ratio (50.82%) for pathogenⅢ. And the Diniconazole has strong inhibition topathogenⅡ.