Study On The Pathogen Of Fusarium Wilt Of Acer Negundo

As a rare colorful-leafed maple tree with high ornamental value,Acer negundo is widely grown in North China and Yangtze River Delta Region for urban greening.In recent years,due to poor management,interplanting under forests and lax detection of imported seedlings,Fusarium wilt occurred in the planting area of Acer negundo in Pizhou City,Jiangsu Province,which not only destroyed the local ecological environment,but also brought economic losses to local farmers and related enterprises.In this paper,the isolate of diseased trees were collected and selected,the pathogenicity was tested with the Koch’s postulates.Then,the pathogen was identified,and its biological characteristics were determined.We preliminarily revealed the pathogenicity mechanisms from duct blockage,enzyme production and toxin theory.At the same time,the germicides with good inhibitory effects on the pathogen were screened out,which provided theoretical basis for the prevention and control of the disease in production practice.The main results are as follows:1.A one-year investigation was carried out on the planting plots,we summarized the occurrence regularity and main characteristics of Fusarium wilt of A.negundo.The investigation indicated that the disease spreads fast and the mortality rate is high.The outbreak period of the disease is from July to August,which suggested that the high temperature in summer has no inhibitory effect on the occurrence of disease.The leaves of diseased trees were wilting and yellowing,the roots were rotted and the xylem became discolored.2.Seven species of fungi and five species of bacteria were isolated from the discolored root and trunk of the infected plants.After inoculation,only the plants inoculated with An7 showed similar symptoms to the natural ones.According to Koch’s law,the pathogen of Fusarium wilt of A.negundo was determined.3.It was initially identified as Fusarium oxysporum by morphological observation,and the Blast result showed that the ITS sequences of the pathogen were 100%homology with F.oxysporum.The phylogenetic tree based on cmdA,RPB2 and TEF-1αsequences showed that the pathogen was clustered in the same branch with Fusarium nirenbergiae.This is the first report of Fusarium wilt of A.negundo caused by F.nirenbergiae.4.The biological characteristics results suggested that PDA medium was the most appropriate for mycelium growth,the appropriate carbon and nitrogen sources were maltose and tryptone,respectively.The fast mycelium growth was obtained at 25°C and pH range from 8.0to 9.0.The highest sporulation was observed at 30°C.Carbon source had little effect on the growth of pathogen,but ammonium nitrogen had inhibitory effect.The germination of conidia needs nutritional support and the lethal temperature was 58℃.5.A preliminary study on the pathogenicity mechanisms of wilt of A.negundo showed that duct of infected plants were hardly damaged and the decay of root epidermis may be related to the high activity of the pathogenic cellulase and pectinase.The crude toxin of the F.nirenbergiae had strong wilting and thermal stability.6.The antagonistic effects of seven chemical agents on F.nirenbergiae showed that the low concentration of prochloraz and carbendazim had best inhibitory effect on the colony growth,and the EC₅₀ were 0.0492μg/mL and 0.6266μg/mL.Followed by benomyl and thiophanate methyl,EC₅₀ were 2.0468μg/mL and 18.5291μg/mL respectively.The spores were highly resistant,and the inhibition effect of Ethylicin on spore germination was the best,EC₅₀ was 1.5941μg/mL,followed by mancozeb and prochloraz,EC₅₀ were 1.5941μg/mL and 6.5046μg/mL respectively.