| Iris japonica Thunb. is a kind of rare uncultivated flower. It belongs to Iridaceae and Iris. It is many-year-life grass plant. It disperses the area of south to Changjiang River, such as Province Zhejiang , Province Fujian, Province Hunan, Province Hubei, Province Guangdong, Province Guangxi, Province Sichan, Province Guizhou, Province Yunnan et. Its leaves long and wide , which has good resistance to poisonous gas. And its flower is beautiful. So it is suited to afforest in city. Then in recent years, it is be introduced to all provinces of China to be cultivated and be applied.Iris japonica Thunb. is also a kind of medicinal herb which has function of detoxification and detumescence . It is used to clear out intestines and stomach. And it is also used to alleviate pain caused by hepatitis , liver swelling , throat and stomach.Iris japonica Thunb. is a kind of common beautifying plant in area of Chongqing where Summer is hot and wet . In recent years, a new disease is found on it , which severely breakdown the function of Iris japonica Thunb. as a kind of beautifying plant. The symptom of the disease is as follows: at first, there is a yellow and green little spot with a brown halo , then, little spots become large ellipse or irregular spots, which diameter reaches 10cm long and 3cm wide ;at last large spots connect together. So the plant looks like to be fired.In order to find out the disease's occurrence pattern and the proper measures to control it effectively, we do the studies such as isolate and differentiate pathogenic fungus and look out the pathogenic fungus belongs to which kind fungi and name the new disease. Then we also have studied some biological characteristics about the pathogenic fungus. And finally we have tested the controlling effect of four kinds of fungicides on PSA , at the same time on plant in greenhouse. And the findings are as follows:1 .Isolation and pathogenicity testIsolate the pathogenic fungus, and gain a kind of Fusarium . Then inoculated the healthy plant in three ways, we found the plant has the same symptom with the speciemen we have gathered. Then isolated from the plant again , the fungus is the same fungus with have isolated from speciemen. So we can say the isolated fungus is the pathogenic fungus . Every way we applied in inoculation showed the pathogenic fungus have strong pathogenicity.2.1dentification of the pathogenic fungus of Iris japonica Thunb. rot spotSingle-spore isolates was cultivated under standardize condition. Average colony diameter was measured from three plates of the fungus after cultivating it at 24℃ for 4 days. The pathogenic fungus were cultured on PSA slants for 7-10 days at 24℃ under cool-white fluorescent lights with a 12-hr photoperiod. Spore's shape and size of conidiaand chlamydospore, the morphology of aerial mycelium, were observed and recorded photographically. The pathogenic fungus were cultured on PSA and on cooked rice slants for 14-30 days at 24℃ under cool-white fluorescent lights with a 12-hr photoperiod,the pigmentation was recorded . And the results are as flows:On PSA , the fungus grows rapid ,with aerial mycelium abundant, silk-like ,white . Coloies reach 2.5-4.1cm for 4 days at 24℃. Macroconidia are rare. Their form is slightly sickle-shaped, thin-walled ,colorless with an attenuated apical cell and a foot-shaped basal cell. 1-6 septates ,10-55×2.5-5.5μm .Mostly 3 septates , 23-32×3.5μm . Microconidia is produced in false heads , generally single-celled, elliptical to allantoid 6-12.5×1.5-3.75μm, colorless. Chlamydospore was form in hyphae, terminal or intercalary, solitary, in pairs of in chains or in macroconidia ,6-10μm in diameter.So by its morphology, cultural character and pathogenicity, the pathogen of rot spot of Iris japonica thunb. was identified as Fusarium oxsporum schl. according to the classification system of Fusarium by Booth. 3. Some biological characteristics of the pathogenic fungusThe experiment finding show: the optimum temperature for the growth of fungus mycel...
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