Pathogen Identification And Chemical Control Techniques Of Coral Leaf Spot

In September 2020,a leaf spot disease of coral tree(Viburnum odoratissimum)was found on the campus of Anhui Agricultural University,and a review of the relevant literature revealed no relevant reports of this disease.To effectively control the leaf spot disease of coral trees,the authors investigated four major parks in Hefei(Bao Park,Hefei City Botanical Garden,Luzhou Park and Peninsula Park)and the campus of Anhui Agricultural University(approximately 0.5ha)and the results showed that the incidence of leaf spot disease reached 60%in more than 100,000 coral trees planted in these areas.Through sampling isolation and identification,verified by Koch’s rule and identified by molecular biology,it was clear that the causal agent of leaf spot disease of coral trees is Neofusicoccum parvum.The biological characteristics of Neofusicoccum parvum,the inhibitory effect of five fungicides on the pathogen and the control effect in the field were investigated,with a view to providing reference for the occurrence,prevalence and control of leaf spot disease of coral trees.The main findings were as follows.1.Isolation and identification of pathogenic bacteria and determination of pathogenicityThe pathogenic bacteria were isolated and purified by tissue isolation and formed white cotton wool colonies on PDA medium.The colonies are initially white,but later the mycelium becomes grey-black with well-developed aerial hyphae.In the double autoclaved pine needle water agar medium can produce conidia,black spherical or irregular shape,the pathogen conidia are oval or ovate,single spore,size is about 16-17μm length,5-6μm width.,conidia early colorless transparent,no septum,later gradually become brown.The pathogen’s internal transcribed spacers(ITS),Elongation factor 1-alpha(EF1-α)and Part of the β-tubulin(TUB2)genes were analysed by multiple gene clustering.A phylogenetic tree was constructed and the pathogen and Neofusicoccum parvum strain MAR2134 were found to be in the same family with a 92%support rate.A combination of morphological observations and molecular identification identified Neofusicoccum parvum as the causal agent of coral tree leaf spot disease.2.Biological characteristics of Clostridium perfringens,a small new crustacean of coral tree leaf spotThe growth of Clostridium perfringens was measured in different temperatures,light,pH,selective media and media with different carbon and nitrogen sources.The results showed that the pathogen was able to grow between 5 and 40℃,with the fastest growth rate at 30℃.The lethal temperature of the pathogen was 52℃ for 10 minutes,and its growth was promoted by light.The best growth was achieved in the test medium with sucrose and peptone as carbon and nitrogen sources.3.Inhibitory effect of five fungicides on Clostridium perfringens and the effect of field agentsThe inhibition effect of five fungicides,namely carbendazim,tebuconazole,imidacloprid,propiconazole and flusilazole,on the mycelial growth of Clostridium neoformans was studied by indoor virulence assay,and the results showed that flusilazole had the best inhibition effect,with EC50 and EC90 values of 0.0291μg/mL and 0.1820μg/mL,followed by imidacloprid,with EC50 and EC90 values of 0.0500μg/mL and 0.1935μg/mL respectively;carbendazim and tebuconazole were more effective with EC50 values of 0.1515μg/mL and 0.1755μg/mL respectively and EC90 values of 3.2730μg/mL and 0.5007μg/mL respectively;the least effective was propiconazole with EC50 and EC90 values of Two fungicides with good cost performance,40%carbendazim and 12.5%tebuconazole,were selected for field experiments by diluting a certain number of times,and the results showed that 40%carbendazim diluted at the same number of times was more effective than 12.5%tebuconazole.The best control effect was achieved by diluting 500 times of 40%carbendazim,with 93.69%and 90.20%control effect 7d after the first and second doses respectively;followed by diluting 800 times of 40%carbendazim,with 72.61%and 86.85%control effect 7d after the two doses.The worst control effect was 12.5%tebuconazole diluted 1000 times,with 35.14%and 22.79%control effect 7d after the first and second doses respectively.