Identification Of The Pathogen And Study Of Epidemiology On Rice Curvularia Leaf Spot

Rice Curvularia Leaf Spot is a new and destructive disease of Rice in recent years.The symptoms of the disease and the isolation and identification of the patho gen was studied on this paper.Form the botanical epidemiology,this paper also studi ed biological characteristics,host range and infection process of the pathogen.Also th is studies investigated different varieties of rice,fertilizer and meteorological conditio n how to influence the occurring and spreading of the disease.In addition,experiments were conducted on the inhibition of 8 fungicides to mycelium growth and spore ge rmination.The main results for this study are as follows:1.Symptoms of disease and the pathogen identificationThe Curvularia leaf spot of rice appears mainly on the leaves.In the beginning,small pale spot appeared on the middle of vein,which gradually developed into spindlydark brown spot.The internal color becomes shallow,middle dark brown,peripheral yellow halo.The pathogen of Rice Curvularia Leaf Spot was identified as C.lunata based on its morphology and the analysis of sequence of ribosomal rDNA-ITS.The morphology characteristic showed that the colonies were dark brown with even and villous edges.Its aerial myceliumwas no evident.The number of spores is large.Conidia were brown,smooth,fusiform,geniculate or hook-shaped,18 to 25 × 5 to 12 ?m,and 3-septate,with the third cell from the base larger and darker than the others.2.The biological characterstics of pathogenThe temperature range for mycelium growth was 10-40?,The optimum temperature for mycelium gorwth was 25?.The temperature range for sporulation was 15-40?,and for sporulation 20?.The temperature range for sporulation was 10-40?,Conidia germinated at 10 to 35?,with optimum temperature between 25 and 30?.The lethal temperature of hypha of pathogen was 53? for 10 min.pH value range for hypha's growth and sporulation was 4~10,the optimum between7.pH value range forsporulating was 4 ~ 11,The optimum pH value for sporulating was pH6~8.This fungus culture in the environment of continuous darkness,continuous alternating light and dark.The studies revealed the optimal illumination condition for growth of mycelium was illumination and darkness facilitated spotulation,but the spore germination was not significant effect.The optimun carbon of mycelial growth and sporulation was sucrose.The followingorder was glucose,fructose,maltose,lactose and starchin.Under the condition of no carbon,hyphae grew faster,but the colony mycelia was extremely thin.In czapek medium,different carbon source middle spores content was not high.The optimal nitrogen source yeast for pathogen hypha growth was yeast extract.The following order was beef cream,NaNO3,peptone,the worst nitrogen soure was NH4 Cl.Under the condition of no nitrogen,hyphae grow faster,but the colony mycelia was extremely thin.In czapek medium,different carbon source middle spores content was not high.Nitrogen source help spore improve germination rate.Spore germination rate was more than 90%,the following order was the beef extract,peptone and sodium nitrate.The worst nitrogen source was yeast extract.4.The study of epidemiology on Rice Curvularia Leaf SpotThe rate of ‘Liang You 0293's disease leaves was lowest rates at 1.10%,and the rate of‘Shen Liang You 5814's disease leaves was as high as 8.59%.The rate of disease leave was 4.76% after adding soil conditioner and the rate was4.11% when did not add.The rate was 8.28% and 9.62%,when add and did not add biological organic fertilizer.The rate of disease leave was 3.92% after applyinging compound microbial fertilizer and the rate was 3.11% when did not add.The rate of disease leave was 4.78% after adding rotten agent.Curvularia lunatus overwinters in the diseased plant body.The disease developed in favor of high temperature and high humidity during July ~ August or the rainy season.The rice leave were invaded by conidium,but not pores.The incubation period was 3-4days.5.The fungicides virulence of pathogen of Rice Curvularia Leaf SpotThe bioassay was carried out screening fungicides to inhibite the fungus.The r esults showed that the best inhibition against myceila of curvularia was propiconazol e with EC50 was 0.2044 ?g·mL-1.and the following was diniconazole and iprodione,whose EC50 was 0.3104,0.6681 ?g·mL-1 respectively.The EC50 of shenqinmycin and difenoconazole were 1.1351 ?g·mL-1and 2.0107 ?g·mL-1.The worst fungicides was carbendazim,thifluzamide and azoxystrobin against myceila of curvularia.The best in hibition against spore germination of curvularia was iprodione with EC50 was 0.1348 ?g·mL-1.The following was diniconazole,difenoconazole,carbendazim,shenqinmycin and propiconazole.Thifluzamide and azoxystrobin were the worst against spore germi nation.