Pathogens Identification And Indoor Fungicides Screening Of Two Litchi Trunk Diseases

Litchi is not only a famous tropical and subtropical fruit,but also an important economic crop in Southern China.The development of the litchi industry plays an important role in the economic growth of Southern China.In the past two years,two kinds of trunk diseases were found in many litchi orchards in Guangdong,Guangxi,and Hainan Provinces,which were named litchi stem rot and litchi line blight respectively according to their symptoms.The incidence of these two diseases is not ferocious,but the spread rate is fast,causing a lot of economic losses to local litchi farmers.In this paper,pathogen identification,biological characteristics test,and indoor fungicide screening for these two kinds of litchi trunk diseases were carried out to investigate the causes of these diseases and lay a foundation for their occurrence regularity and control research.The research results are reported as follows:1.The pathogens of these two kinds of litchi trunk diseases were identified.The pathogens of litchi diseases in Guangdong,Guangxi and Hainan were identified by pathogen isolation,pathogen purification culture,morphological observation,pathogenicity test,and molecular biology methods.The pathogen of litchi stems rot was Lasiodiplodia theobromae(Pat.)Griffon & Maubl.and Fusarium decemcellulare Brick,litchi line blight was Corticium sp.respectively.2.Among the biological characteristics,the most suitable medium for the growth of Lasiodiplodia theobromae,Fusarium decemcellulare,and Corticium sp.was PDA medium.The best carbon source of the three pathogens was mannose.Lasiodiplodia theobromae can grow in the range of 15 ℃ ～ 40 ℃,and the optimum temperature is 30 ℃.The optimum growth p H is 7.Fusarium decemcellulare can grow in the range of 15 ℃ ～ 35 ℃,and the optimum temperature is 30 ℃.The optimum growth p H is 6-9.Corticium sp.can grow in the range of 15 ℃ ～ 30 ℃,and the optimum temperature is 25 ℃.The optimum growth p H is 4.Light has no obvious effect on the colony growth of the three pathogens,the optimum germination humidity of Lasiodiplodia theobromae spores was 90%.The optimum germination humidity of Fusarium decemcellulare large conidia was 90% ～ 93%,and the optimum germination humidity of Fusarium decemcellulare small conidia was 90%.3.Indoor toxicity test of fungicides to Lasiodiplodia theobromae,Fusarium decemcellulare,and Corticium sp.,five fungicides including 50% carbendazim,25%bromofenitrile,50% carbendazim,50% carbendazim and 30% benzoconazole effectively inhibited the growth of Lasiodiplodia theobromae colony,with EC50 values ranging from0.053 μg/m L to 16.411 μg/m L.In the toxicity test to Fusarium decemcellulare,three fungicides including 50% carbendazim,25% bromopropionil,and 30% benzoconazole effectively inhibited the growth of Fusarium decemcellulare colony,with EC50 values ranging from 1.185 μg/m L to 18.502 μg/m L.In the toxicity test to Corticium sp.,three fungicides including 40% chlorothalonil,25% bromopropiconil,and 30%benzopropiconazole effectively inhibited the growth of Corticium sp.colony,with EC50 values ranging from 2.1 μg/m L to 17.000 μg/m L.