Study On The Occurrence Of Poplar Powdery Mildew And Its Chemical Control In Xinmin District Of Shenyang City

Poplar is one of the main tree species in fast-growing and high-yielding forests in the northern region of China,and it is also the first tree species being planted in Liaoning Province.At present,the price of poplar in the market is increasing,and it is facing a shortage of large-diameter timber,the characteristics of poplars are asexual reproduction and fast growth,which can be used to solve market supply and demand problems,as well as improve productivity and land utilization.Therefore,poplars have very high economic benefits,at the same time,poplar is an important tree species in the construction of shelterbelts and surrounding green forests.It can improve the ecological environment,so as to improve the ecological and social benefits.In recent years,poplar powdery mildew seriously attacts poplar in Shenyang,therefore,how to effectively control the desease is an urgent problem in this area.At present,there are few report on systematic studies of poplar powdery mildew.The study targeted poplar powdery mildew in Shenyang,and systematically studied the identification of the pathogenic bacteria,the biological characteristics of the pathogenic bacteria,the specific time and corresponding symptoms of the occurrence of forest diseases,the dynamics of the spatial spread of spores,and the control of pesticides,the main findings are as follows:1.The test used traditional morphology and modern molecular biology techniques to identify pathogenic bacteria,it was found that Phyllactinia populi(Jacz.)Yu was the pathogen causing poplar powdery mildew in this area,and its asexual type was Ovulariopsis sp.Through the inoculation test,it was confirmed that the cleistothecia was the first source of infection of the next year’s poplar powdery mildew,and the conidiospore was the source of reinfection.2.This test measured the biological characteristics of the powdery mildew pathogen of poplar,first,the wintering ability of the cleistothecia was measured,and the results showed that the wintering ability of the cleistothecia was stronger in the forest,and for the first time,it was found that the overwintering viability of the cleistothecia was significantly positively related to the number of ascospores in the cleistothecia,and the cleistothecia was extremely resistant to low temperatures.Secondly,the development and maturity of the cleistothecia after overwintering was observed,and it was found that the cleistothecia began to mature in mid-April 2019,and precipitation was beneficial to the maturation of ascospores.Finally,the effects of environmental factors on the germination of conidiospore were studied.The results showed that conidiospore could germinate at 20-30℃,the optimum temperature was 25℃,and the relative humidity was 93%,the p H value is 8,and the most suitable carbon source for germination is mannitol and galactose.Each nitrogen source(ammonium chloride,potassium nitrate,L-arginine,glycine,urea,peptone)has a certain inhibitory effect on the germination of conidiospore,and the requirements for light conditions are not strict,but oxygen is a necessary condition,the lethal temperature of conidiospore was 45℃ for 10 min.3.The trial continuously observed and recorded the occurrence time and symptoms of forest diseases in the test sites in 2018 and 2019,the results showed that the incidence of powdery mildew of poplar in 2018 began from mid-August to mid-September,fruiting bodies appeared from early September to early October,and the powdery layer gradually subsided from late September to late October.The disease progress in 2019 generally precedes 2018,and the onset begins in early July to late August.Fruiting bodies begin to appear in mid-September to early October,and the white powder layer subsides from mid-September to late October.For two consecutive years,Populus cathayana×canadansis ?Xinlin1‘ and Populus×euramericana cv.?Guariento‘ had the fastest disease progression,followed by Populus×euramericana cv.?N3930‘ and Populus×xiaozhuanica cv.?Zhangwu‘,and Populus liaoningensis Z.Wang et H.D.Chen cv.nov had the latest onset.In addition,the spore-capturing technology was used to study the diffusion dynamics of conidia in the forest.The results showed that the spore diffusion amount increased first and then decreased with the increase of canopy height,and the spore diffusion amount in the middle canopy most.During the growing period of poplar,the incidence and disease index were linearly positively correlated with the spore spread,with correlation coefficients of 0.69 and 0.87,respectively,and precipitation significantly inhibited the spread of interspore spores.4.The toxicity of 10 fungicides was determined by the method of slide spore germination,the results showed that 42.4% zolyl ether · fluoroamide SC,43% fluorobacterium·oximeryl ester SC and 42% benzophenone SC had the best virulence,and their EC50 values were 134.25 mg/L,160.26 mg/L and 177.36 mg/L,respectively.In the sample plot at the end of July 2019,three kinds of fungicides selected from the laboratory were used to control the poplar powdery mildew in the forest.The results showed that the control effect of 42.4% zolyl ether·fluoroamide SC 400 times solution was the best,and that of 43% fluorobacterium·oximeryl ester SC 200 times solution was the second.