The Biological Characteristics, Pesticide Screening And Variety Resistance Analysis Of Rice Flax Leaf Spot Pathogen

Rice is an important grain crop in China,and the disease of rice seriously affects the grain yield,which is a key problem for scholars to solve.Rice brown spot disease is a kind of fungal disease,which has a wide range of diseases.It has been found in every rice area in China.When the rice is malnourished and the growth is poor,the disease is very serious.Due to the lack of related research on this disease,when a large number of rice brown spot occurred,it could not be well controlled,resulting in serious economic losses.In this experiment,the pathogen was isolated and identified from the field,and the biological characteristics of the pathogen of Bipolaris oryzae were studied from five aspects:temperature,light,pH,source of carbon and nitrogen.Determination of virulence of 20 insecticides against Bipolaris oryzae by growth rate method in the laboratory,and the EC₅₀ value was calculated.At the same time,29 major varieties of Heilongjiang rice were selected to evaluate the resistance of rice brown spot in order to provide reference for the control measures and mechanism of disease resistance of Heilongjiang rice brown spot.The main contents and results of the study are as follows:1.Observation and morphological identification of bacterial colonies,hyphae,conidia and conidia of pathogenic bacteria.Molecular identification was carried out by homology comparison of ITS nucleic acid sequence,and the pathogen was identified by back connection.The color of bacterial colony was black and brown,and the texture of bacterial colony was fluffy and fluffy without exudate.Conidial color is brown,spindle-shaped or cylindrical;The conidiophore is brown and curved.The obtained pathogen ITS region sequence was 99%similar to that of Cochliobolus miyabeanus in Genbank.The isolated pathogens were prepared as spore suspension and inoculated in rice leaves.The central color of the disease spot was dark brown to off-white,with brown edges and different shades of yellow edges in the outer ring.The morphology of the disease spot was consistent before and after inoculation,and the isolated pathogen could be identified as rice brown spot（Bipolaris oryzae）.2.The effects of temperature,light,pH,carbon source and nitrogen source on mycelium growth and colony morphology of Bipolaris oryzae were studied.The results showed that the optimum growth conditions for the pathogen of Bipolaris oryzae were alternation of light and dark,pH of 7,25℃and soluble starch and glycine as carbon and nitrogen sources.3.The bacterial growth rate method was used to determine the susceptibility of Bipolaris oryzae to antimicrobial agents.Among the 20 agents tested,20%benzopropiconazole,45%prochloraz,32.5%benzoin,12.5%diniconazole,40%chlorothalonil,50%kresoxim-methyl,10%Jinggangmycin,10%phenylethylcyclazole,43%tebuconazole,The EC₅₀ value of 75%mancozeb was less than 0.1000μg/mL.The best fungicide was30%benzopropiconazole and its EC₅₀0 value was 0.0002μg/mL.The least effective fungicide was 80%ethylicin,and its EC₅₀ value was 4.3945μg/mL.4.The resistance of 29 rice varieties to rice brown spot was studied by artificial inoculation in Heilongjiang province.Among them,there were no rice varieties that showed resistance to rice brown spot,and there were 6 varieties that showed moderate susceptibility（MS）to rice brown spot,accounting for 20.7%of the tested rice varieties.There were 23 rice varieties with high susceptibility（HS）to rice brown spot,accounting for 79.3%of the tested rice varieties.