Investigation Of Lettuce Diseases And Screening Of Fungicides In Beijing Area

Due to the lettuce planting area increasing,lettuce diseases occur easily during the cultivation period which cause the lettuce grow weakly,reduce lettuce yield and affect consumption,storage and transportation of post harvest lettuce.In order to make clear the occurrence of lettuce diseases in Beijing area,the disease of different lettuce varieties in different districts was investigated and pathogens were identified,and then fungicides to two lettuce pathogenic fungi was screened by indoor toxicity test.The study can help the cultivation and disease control work of lettuce and main results are as follows.From April,2017 to March,2019,there are four fungal diseases,two bacterial diseases and lettuce virus diseases during the growth period of lettuce planted in greenhouse in Beijing area.Fungal diseases include lettuce downy mildew?Bremia lactucae?,lettuce gray mold?Botrytis cinerea?,lettuce sclerotium?Sclerotinia sclerotiorum?and lettuce black spot?Alternaria alternata?.Bacterial diseases include lettuce leaf edge necrosis?temporarily??Pseudomonas marginalis pv.marginalis?and lettuce soft rot?temporarily??Pectobacterium carotovorum?.Lettuce diseases were investigated in different areas of Beijing including Changping,Fangshan,Shunyi,Daxing,Yanqing,Pinggu and Tongzhou 7 districts.Firstly,the diseases occurrence of different lettuce varieties in Changping district was investigated and lettuce downy mildew,lettuce gray mold and lettuce soft rot happened.The incidence of above three lettuce diseases of 10 different lettuce varieties was investigated,no disease was found in the'North Sansheng 2'variety in the early period.The incidence of lettuce downy mildew and lettuce gray mold of 24 different lettuce varieties in different periods was investigated in the later period and above two diseases were not found on lettuce varieties'HZB-16?'PF-LE-4'and'Red wrinkle'during the whole growth period.Except Changping district,lettuce diseases in other districts in Beijing area were investigated and lettuce downy mildew,lettuce gray mold,lettuce sclerotinia,lettuce leaf edge necrosis and lettuce soft rot happened.Indoor toxicity of 12 fungicides on A.alternata and 7 fungicides on B.cinerea both infecting lettuce were tested by the mycelium growth rate method..The results showed that 10%difenoconazole had the strongest inhibitory effect on the mycelium growth of A.alternata of which the EC₅₀0 was 1.82?g/ml.75%chlorothalonil has the strongest growth inhibitory effect on the mycelium of B.cinerea and its EC₅₀0 is 15.14?g/ml.Primers LMV-24F and LMV-24R could be used to detect Lettuce mosaic virus from the lettuce leaves by RT-PCR.Through sequence determination and analysis,the partial sequence about 220bp of LMV in Changping lettuce samples was obtained.