Pathogen Identification,Biological Characteristics,and Laboratory Fungicides Screening Of Five Diseases On Avocado

Avocado（Persea americana Mill.）is an evergreen tree,which is belonging to Lauraceae family,Persea genus.In recent years,with the expansion of avocado planting area in Hainan Province,diseases is becoming more serious.But,China reported diseases of avocado were less than 1/3 of abroad.So,this article carried out preliminary studies on5 diseases,including pathogen identification,biological characteristics and fungicides screening in laboratory,the results are as follows:Phytophthora cinnamomi the causal agent of avocado root rot,mainly damaged the roots of the avocado.The main symptoms in the field were as follows:the leaves became yellow,the branches withered,the roots became black and rot,and the plants died in the end.The pathogen oomycetes was identified by isolation and purification,pathogenicity test,morphology and multi-gene（ITS,LSU,and COXII）phylogenetic analysis.And the biological characteristics and 12 fungicides against screening in laboratory were determined.Results:P.cinnamomi was the pathogen of avocado root rot.The suitable medium was PDA,temperature was 28℃,pH was 8,light condition was 24 hour dark,and Oxathiapiprolin had a strong toxicity to P.cinnamomi,with the EC₅₀reaching 0.0002μg/m L,followed by Dimethomorph,its EC₅₀was 0.0929μg/m L.Avocado seedling black-stem disease mainly damaged stem-base.The main symptoms in the field were black brown streaks at the base of the stem,and white powder on the lesions,which caused the leaves to turn yellow and the plants to wither and die.The pathogen oomycetes was identified by isolation and purification,pathogenicity test,morphology and multi-gene（ITS,TUB2,TEF,COXⅠ,and COXⅡ）phylogenetic analysis.The biological characteristics and 12 fungicides against screening in laboratory were determined.Results:Phytophthora palmivora was the pathogen of avocado seedling black-stem.The suitable medium were PDA and CMA,temperature was 30℃,pH was 8,light condition had no effect,and Oxathiapiprolin had a strong toxicity to P.palmivora,with the EC₅₀reaching 0.0005μg/m L,followed by Metalaxy1+Propamocarb and Flumorph+Metalaxyl-M,EC₅₀were 0.0648μg/m L and 0.0698μg/m L,respectively.Avocado branch blight disease mainly damaged branch.The symptoms in the field were that tan,water-soaked lesions were produced on the branches,and abundant small black spots（pycnidia）were produced on the lesions.At the later stage,the white powder were formed on the lesions,which eventually caused death of the branches.The pathogen fungi was identified by isolation and purification,pathogenicity test,morphology and multi-gene（ITS,TUB2,and TEF）phylogenetic analysis.The biological characteristics and12 fungicides against screening in laboratory were determined.Results:Lasiodiplodia theobromae was the pathogen of avocado branch blight.The suitable medium were PDA,PSA,and MEA,temperature was 30℃,pH was 6,light condition had no effect,and Carbendazim had a strong toxicity to L.theobromae,with the EC₅₀reaching 0.0594μg/m L,followed by Benomyl,its EC₅₀were 0.0838μg/m L.Avocado stem-end rot disease of Botryosphaeria dothidea damaged fruit.Dark brown to brown lesions appeared on the fruit,the flesh became light brown,and later extended to the whole fruits,leading to fruits rot.The pathogen fungi was identified by isolation and purification,pathogenicity test,morphology and multi-gene（ITS,TUB2,and TEF）phylogenetic analysis.The biological characteristics and 12 fungicides against screening in laboratory were determined.Results:B.dothidea was the pathogen of avocado stem-end rot.The suitable medium were PDA and PSA,temperature was 30℃,pH was 6,light condition was 12 light/12 dark,and Carbendazim had a strong toxicity to B.dothidea,with the EC₅₀reaching 0.0881μg/m L.Avocado Corynespora leaf spot damaged leaves.The symptoms in the field were irregular dark brown disease spots on the leaves,obvious yellowish margin around the lesions,and slightly raised on the adaxial side of the leaves,which eventually causing severe defoliation.The pathogen fungi was identified by isolation and purification,pathogenicity test,morphology and multi-gene（ITS,TUB2,TEF,and ACT）phylogenetic analysis.The 13 host ranges of plants,biological characteristics and 11 fungicides against screening in laboratory were determined.Results:Corynespora cassiicola was the pathogen of avocado Corynespora leaf spot.There were 8 plants showed obvious symptoms,including Betelnut,Plantain banana,and so on.The suitable medium were PDA,PSA,MEA,and Czapek,temperature was 30℃,pH was 7,light condition was 12 light/12dark,and Benomyl had a strong toxicity to C.cassiicola,with the EC₅₀reaching 0.2943μg/m L,followed by Carbendazim and Prochloraz,EC₅₀were 0.3331μg/m L and 0.5223μg/m L,respectively.The research results above not only provide relevant theoretical basis for the prevention and treatment of avocado 5 diseases,but also has great significance to the sustainable development of avocado industry in Hainan Province.