Identification, Biological Characteristics Of The Pathogen And Fungicides Screening In Laboratory For Dichondra Brown Leaf Spot

Dichondra repens Forst. been called loosestrife, belongs to Dichondrae of Convolvulaceae. It is a permanent herb plant, and can be used as turfgrass in gardening. It was also an important element in many Chinese medicines.The Dichondra brown leaf spot was new disease in the world. In 2005, the percentage of the disease leaves reached 90%, and spot number on one leaf reached 86, which caused the decline and death of the grass. The dissertation included the symptom characteristics, the identification of pathogen, the biological characteristics, the disease cycle, the fungicides screening in Laboratory of Pyrenophora dichondrae Brown Leaf spot and the POD, PPO isozyme activity.1 Symptom characteristicsThe Dichondra brown leaf spot main did harm to the leaf, and also the pericles. At first, chlorosis spot as small as pin was on the leaf. Later, the spot changed to little brown in the center, and dark brown in the leaf margins. The shapes were circular, elliptical and irregular. Many dark spots called ascos were on the back leaf in the moist temperature.2 Identification pathogenJudging from the shape characteristics and description of Ascomycetes by Hanlin, identified it as Pyrenophora dichondrae sp. nov. It belongs to Pleosporales, Dleosporaceae, Pyrenophora.3 Biological characteristicsFor the growth of pathogen, the optimum media were PDA, PCA and oat, the optimum C source were dextrose and mannitol, calcium nitrate and potassium nitrate were the optimum N source. The temperature and pH rage suitale the growth of Pyrenophora dichondrae sp. nov. were wide. The optimum temperature was 25～28℃, and the optimum pH was pH6～9. Whole dark promoted ascospore formation, and whole light promoted mycelium growth. For ascospore formation, the optimum media and temperature were PDA and 25～28℃respectively. The optimum pH was pH5～8. Dextrose and amylum were the optimum C source, and calcium nitrate was the optimum N source. For ascospore germination, the optimum temperature and pH were 20～28℃and pH6～8 respectively. The optimum RH was RH90%～100%. Dextrose was the optimum C source, and sodium nitrate was the optimum N source.4 Disease cycleThe over wintering of pathogen were ascospore and mycelium. Pyrenophora dichondrae sp. nov. disseminated by air, rain and dead tissue. It infected host through germ tube from stomata and cell gap.5 Fungicides screening in LaboratoryInhibiting dissertation of 6 fungicides on Pyrenophora dichondrae sp. nov., the results were that: the best fungicides inhibiting mycelium growth and ascospore germination were Kajundan, Duojunling, and Baijunling. And the second were carbendazim and thiophanate-methyl. The worest was copper-acetate.6 Damage of Dichondra brown leaf spot to Dichondrae repens from different placePercentages of unhealthy leaves from different place were different. The heavest was Dichondra repens from Yaan (95%, Sichuan province), the second were from Kedu (Yunnan province), and the lest was from Shandu (40%, Guizhou province). Disease index were different by their hometown. The hingest was from Yaan, the second were from Shandu and Kedu, and the lowest from Dushan.7 Isozyme activity's variety of diseased and undiseased leaves damaged by Dichondra brown leaf spotIsozyme activity dissertation showed that: 4 Dichondrae repens material had their PPO and POD isozyme activity's variety respectively. For the materials from Yaan and Shandu, the unhealthy leaves' isozyme activity was hinger than healthy leaves'. For the material from Dushan, the healthy leaves' isozyme activity was hinger than unhealthy leaves', but the material from Kedu was on the contrary.