Identification Of Pathogen Causing Pear Black Spot In Alar And Screening Of Controlling Fungicides In Laboratory

Object: In recent years,korla pear production has suffered serious losses due to black spot disease.This research aimed to identify the pathogens causing Korla pear black spot in Alear,Xinjiang,and to screen fungicide to control the disease.Methods: The total of 41 korla pear fruits showing dark spot were randomly collected from the pear garden in Alar city.The method of routine tissue isolation was used to isolate and purify fungi from black spots on pear fruits.The pathogenicity of the isolated and purified strains to fruits of Korla pear and jujube were determined by inoculation with or without wound.Similarly,9 jujube flowers were collected near korla pear garden to fungal isolation and infection assay.Representative strains were selected according to morphological differences of colonies on PDA media.The taxonomic species of the representative strains were identified combining morphological characteristics including sporulating characters,conidia size and the number of septum with phylogenetic trees obtained by analysis single gene locus sequences and multilocus sequences based on alt-a1 gene(Alt-a1),RNA polymerase second largest subunit gene(rpb2),calmodulin gene(Cal),translation elongation factor 1-alpha gene(tef1),-tubulin gene(tub)and OPA2-1 sequences.The effective fungicide against pear black spot were screened by the inhibition rate of fungal growth on PDA medium with fungicide.Results:1.The total of 36 strains were isolated from pears black spot,of which 34 strains were fungi of Alternaria genus and 2 strains were Penicillium spp.,accounting for 94.4% and 5.6% of the total isolated strains;6 strains were isolated from jujube flower,which also were Alternaria genus.2.Black spots similar to natural symptoms were observed at the inoculation site of korla pear at 3 days post-inoculation with wound and 5~7 days post-inoculation with unwound when 34 Alternaria strains from Korla pear were inoculated on fruits of Korla pear;similar black spot symptoms were also observed on jujube fruits when Alternaria strains from Korla pear were inoculated on jujube.Similarly,Alternaria strains from jujube also induced black spot on fruits of Korla pear.It indicated that Alternaria strains from korla pear and jujube were the pathogen causing black spot.3.Strains P3,P8,P21 and P26 were selected as representative strains for taxonomic species identification.The conidiophore of P3 and P8 strains branched short conidial chains composed of no more than 10 conidia;The secondary conidial chains of P3 is shorter than that of P8,consisting of 1~4 conidia;the average conidial size of P3 is 9.5 × 19.1 ?m,with 1-3 diaphragms,whereas the average conidial size of P8 is 9.3 × 20.3 ?m,with 2-5 diaphragms.Strains P21 and P26 were similar in morphology and produced conidial chains in reduced to nonbranching patterns,composed of more than 10 conidia.The average conidial size of P21 is 12.7 × 25.9 ?m and the average conidial size of P26 is 11.0 × 27.4 ?m,both with 3~7 diaphragms.The phylogenetic trees of the 4 representative strains were obtained by analysis single gene locus sequences and multilocus sequences based on Alt-a1,rpb2,Cal,tef1,tub and OPA2-1 sequences,respectively.P3 strain was identified as Alternaria arborescens,P8 strain was identified as A.alternata,P21 and P26 strains were identified as A.tenuissima combining the morphological characteristics and phylogenetic analysis.4.After preliminary fungicide screening,25% imidine diluted by 100 times had the best inhibitory effect on Alternaria spp.,the inhibition rate of fungal growth was 87.1%;40% fluosilazole diluted by 8000 times had inhibition rate of fungal growth with 85.8%;32% phenylpropanecyclozole diluted by 100 times had inhibition rate of fungal growth with 83%;72% frostweil · manganzinc diluted by 150 times had inhibition rate of fungal growth with 69.6%.Conclusion: Alternaria arborescens,A.alternata and A.tenuissima are the pathogens that cause the black spot of korla pear.Alternaria spp.from Korla and Alternaria spp.from jujube were infection sources of black spot of the Korla pear and the black spot of the jujube.Both 25% imidine diluted by 100 times and 40% fluosilazole diluted by 8000 times had inhibitory effect on Alternaria spp.