Study On Etiology Of Cynodon Leaf Spot In Golf Course

Cynodon leaf spot is an important disease in golf courses. The samples is collected from Wuhan Gold-Silver Lake golf course and E-zhou Red Lotus Lake golf course from 2003 to 2005. The pathogen was isolated from the leaf spot and the isolate were purified by single sporing approaches. And then Pathogenicity tests, morphological and molecular identification, biological characteristic of this fungus and infection process on four turfgrass species were studied.This fugus was identified to be Bipolaris australiensis according to the morphology of conidia and conidiophore. The sequencing of the internal transcribed spacer region of this fungus showed 99.61% identity with Cochliobolus australiensis assession AY923860 in the GenBank. The pathogenicity tests showed that the same symptom as seen in the golf courses appeared on the same variety of Cynodon hybrid after inoculation with mycelial plugs or conidial suspension. Reisolation from the margin of symptomic tissue (leaf spot) were successful done to complete fully the Koch's postulates. To the best of our knowledge, this is the first report of leaf spot caused by Bipolaris australiensis on cynodon in Hubei province, China.The result of determining of host range shows that Oryzae sativa, Zea mays, Poa pratensis, Zoysia japonica, Festuca arundinacea, Lolium perenne,Agrostis stolonifera are among the hosts of Bipolaris australiensis.The research on the biological characteristic of Bipolaris australiensis are as follows. This fungus could sporulate under the temperature from 15℃to 35℃, with the most appropriate temperature from 20℃ to 30℃. While the mycelium could grow under the temperature from 10℃ to 38℃, and ceased to grow under 40℃, with the most appropriate from 25℃ to 35℃ .The mycelium could grow in pH value range from 2.76 to 10.75 with the most appropriate pH Value range from 4.86 to 6.41. Among the carbon resourses, mannite is the best for the mycelial growth while Maltose is the worst. As for the sporula-tion, lactose is the most appropriate for the sporulation, while the sucrose is the worst. Amomg the nitrogen resourses, glycine is worst for the mycelial growth, and NaNO₃ is the best. KNO₃ is the best for sporulation, while Peptone is worst.Result of determining of the toxicity of seven fungicides to Bipolaris australiensis show that EC50 of 10% polyoxin B DP, 25% Amistar EC, 50% Carbendazim DP, 80% Mancozeb DP, 50%captan DP, 30%Armure EC, 10% Score GR is 5912.965μg/ml, 1135.283μg/ml, 21.33029μg/ml, 18.24744μg/ml, 9.6468μg/ml, 1.148368μg/ml,...