Etiology Of Curvularia Leaf Spot On Cynodon Hybrid

The Leaf spot is one of important diseases in golf courses. It causes leaf spot and leaf blight on many species of grasses, and can influence sights and destroy quality of grasses. At present there are only reports about the disease investigation and primary chemical control. The aim of this study is to indentify the pathogen of bermudagrass Leaf spot, to understand host range, biological characteristics, and the infection process of the pathogen on four species of grasses. The results showed as follow:Curvularia sp. was isolated from the diseased leaf of Cynodon hybrid in Red Lotus Lake golf courses in E-zhou. Pathogenicity was tested by inoculating the leaf with mycelium plug of Curvularia sp., the result indicated that Curvularia sp. isolate was the pathogen. The morphological characteristic showed that the colonies were black green and the hyphae were septum, brown, Spore size was 11.07×25.18μm, mostly ellipse, with three septate , two central cells were larger than both terminal cells , brown to dark brown , terminal cells subhyaline to light Brown after cultured on PDA medium at 5d. The DNA sequence of ribosomal ITS of the isolates was found to match 99% with an ITS sequence of Curvularia verruculosus in GenBank. According to the morphological characteristics, and the DNA sequence of ribosomal ITS, the pathogen was identified as C.verruculosus. The pathogen can infected four turfgrass species (Cynodon hybrid, Lolium perenne, Agrostis plustris, Poa pratensis) and other gramineous plants ( Oryzae sativa, Blumeria tristic, Zea mays).The studies on biological characteristic revealed that this fungus could grow and sporulate under dark or continuous illumination, the optimal illumination condition for growth of mycelium was alternant illumination and darkness facilitated spotulation.The mycelium could grow under the temperature from 15-35℃, the optimal temperature for the mycelial growth and sporulation was 30℃and 25℃, respectively. pH value range for mycelium growth were 4-12 and pH7 was optimal. pH value range for sporulation were 5-12 and pH6 was optimal. The isolate could utilize various carbon and nitrogen sources, but different carbon and nitrogen sources had different influence for mycelial growth and sporulation. Among carbon and nitrogen sources, starch and yeast extract were best for mycelial growth, D-galctose and CaNO₃ were best for sporulation.The lethal temperature for mycelial growth and spores gemination were 55℃for 10 min, respectively.The result of determining of the toxicity of fungicides to C.verruculosus showed that the six fundicides choosed could inhibit mycelial growth at different concentration. 10% Score GR and 30% Armure EC showed best inhibiting to mycelial growth, but the 10% polyoxin B DP was the worst.Leaves of four turfgrass species (Cynodon hybrid, Lolium perenne, Agrostis plustris, Poa pratensis) were inoculated with conidial suspensions of C.verruculosus. Inoculated leaves were incubated at 25℃under high humidity.Samples were collected from inoculated leaves at different timing intervals,and then decolorated and stained. Observe the infection process on four species of grasses with fluorescence microscope under bright field.. The result indicated that the conidia began to germinate after 3 hours of inoculation, and formed one to four primary germtubes from one or two ends. The rate of conidial germination of C.verruculosus on leaves of four turfgrass species after 3h of inoculation showed no significant differences. After 12 hours of inoculation, the percentage of germination were significantly larger on the Cynodon hybrid and Poa pratensis than on the other two hosts.The pathogen C.verruculosus was able to penetrate host through two paths such as leaf stomata and epidermis.The penetration from leaf stomata was considered as a major way, and can be observed after 6h of inoculation.The rate of pathogen infecting from leaf stomata of four turfgrass species showed significant differences. After 24 hours of inoculation, the percentage of infecting were significantly larger on the Cynodon hybrid and Poa pratensis than the other two hosts. Direct penetration into epidermis was uncommon observed.