| Sichuan is one of the major kiwifruit producing provinces in China,accounts for 56700hm~2of cultivated area during 2018.However,besides rapid increase in growing areas,several biotic factors are greatly impacting in almost all kiwifruit growing orchards of the province.Recently,one of the serious threats to kiwifruit industry is posed by the bacterial canker that cause breakthrough as an epidemic and resulted huge monetary losses to kiwifruit industry.Thus,present studies were conducted to investigate the occurrence and distribution of kiwifruit canker,analyze the population variation of the pathogenic Psa(Pseudomonas syringae pv.actinidiae),and to formulate the integrated management strategies of kiwifruit canker for sustainable production.In current study,a comprehensive general survey was conducted in different kiwifruit growing areas of Sichuan Province from 2015 to 2018 to find out the occurrence and distribution of kiwifruit canker.The key climate factors affecting kiwifruit canker were also analyzed,and further disease division in different regions were predicted using the spatio-and geo-statistical analysis modules of arc GIS software based on climate data collected in the past 30 years.To clarify the regional variation in pathogen,different pathogenic strains were collected from various kiwifruit producing regions and identified using house-keeping genes,gene flow as well as genetic diversity of pathogens through BOX-PCR and EIRC-PCR.In addition,the resistances screening of kiwifruit germplasm were tested in vivo and in vitro to find out the potential material.The integrated disease management measures were also studied to overcome the spread of pathogen and enhance the healthy cultivation for sustainable kiwifruit production.The major results so far achieved are as follow:1.The results regarding the annual occurrence and distribution of kiwifruit canker showed that disease were mainly distributed in Longmen mountain area around the Sichuan basin northward to Guangyuan,connected with Qin-Ba mountain area to form a meniscus distribution.The trend of resistance against canker disease among different kiwifruit cultivars with green,yellow and red kiwifruit were ranked from high to low resistance.There was significantly positive correlation of disease occurrence with growing-area altitude,especially at the altitude of 500m.Kiwifruit canker did not occur naturally at or below 500m altitude,which particularly depends on orchard management level was also noticed.However,it was severely observed in susceptible kiwifruit cultivars grown above 600 m and/or increased over the altitude mainly due to occurrence of Psa.It was observed that bacterial canker disease often occurred more seriously in old kiwifruit trees,and the incidence rate was about 7.6 fold higher in the windward slope that in leeward slope.An annual development dynamic of kiwifruit canker revealed that the initial occurrence of disease symptoms appeared in only few tree branches from November to February of next year.The typical disease symptoms were commonly noticed in the branches and leaves from February to March;and thereafter in the moths of April and May,the symptoms were found hidden in tree stems.The withering and drooping of newly developed shoots,flower rot and diseased leaves were observed during June and August.When temperature became higher,the development of new symptoms stopped in the kiwifruit stems and leaves;however,in the moths of September and October,new leaf spot reappeared in the kiwifruit trees.2.Potential occurrences of kiwifruit cank were investigated in Sichuan Province.For that kiwifruit plantings were mainly divided into four areas including nonviable area for Chinese kiwifruit,potential severe occurrence area,potential suitable occurrence area and potential not suitable occurrence area in Sichuan Province,accounted for 43.8%,26.5%,17.4%and 12.3%,respectively.The nonviable area included Ganzi State and Aba State in the south plateau area of Sichuan except of the marginal area connected to the basin.The potential severe and suitable occurrence area were located along Longmen mountain area,from South to North,connect Qin-Ba mountain area,including all the regions of Yaan,Chengdu,Deyang,Mianyang,Guangyuan,Bazhong,Dazhou,Nanchong and Liangshang,and partial areas of Leshan,Meishan,Suining and Guanan.Three cities including Ziyang,Neijiang and Zigong,combined with partial areas of Luzhou,Yibin,Leshan,Meishan,Suining,Guangan,Panzhihua were considered not suitable for occurrence of kiwifruit canker.3.Three house-keeping genes gap A,gyr B and pfk of pathogenic type of Psa were selected for phylogenetic analysis.The results demonstrated that all strains were identified as Psa-biovar3 type in Sichuan,which was totally consistent with results using biovar3specific primers.When the similarity coefficient was 0.748,Psa strains were classified into five clades by BOX-PCR,and the typeⅢwas the most group with 42.8%frequency,covering all strains from different kiwifruit producing areas.When the similarity coefficient was 0.684,Psa strains were classified into six clades by EIRC-PCR,and the typeⅣwas the most group with 54.3%frequency,covering all strains from different kiwifruit producing areas.According to different ecological areas in Sichuan,63 strains were divided into five populations.The molecular band analysis based on BOX-PCR and EIRC-PCR indicated that the genetic variation of Psa in Sichuan existed within the population,showing strong gene flow.4.Resistance screening of 12 commercial and 48 wild kiwifruit germplasm against Psa was evaluated through methods of variety reference and cluster analysis under in vitro conditions.Amony 12 commercial kiwifruit germplasm,accounting for moderately susceptible rate is 50%,moderately resistant rate is33.3%and resistant rate is 16.7%;Amony48 wild kiwifruit germplasm,accounting for resistant rate is 22.92%,moderately resistant rate is8.33%,moderately susceptible rate is 20.83%,susceptible rate is 33.35%,highly susceptible rate is 14.58%.Among these,11 cultivars were used under in vivo for resistance screening.The in vivo results indicates that Hongyang and 14-01-23C were highly susceptible to canker disease,Jinfeng,Jinyan,14-10-19B and 20-12-05C were found susceptible;while Miliang1,Cuixiang and Haiwote were ranked as resistant cultivars.;4-09-20B was highly resistant.5.Integrated management measures of kiwifruit canker were studied and the results showed that shelter cultivation had an obvious control effect on the canker of kiwifruit especially on stem and leaves.The average control effect from December to April was 84.9%.In the shelter cultivation method,the combination of“shelter cultivation+Songer coating smearing with bactericide+foliar spray”was the most effective and showed significant control on disease development.The average disease index was observed 0.712,and the kiwifruit tree survival rate was accounted for 92.3%.The fruit-hanging rate and fruit-hanging number was significantly higher in treated trees compared to untreated(control)and the control effect was observed as high as 95.61%.The germination rate,average germination length,branch length and diameter were all higher in the treated trees compared to untreated.The percentage of fruiting,size and weight of fruits were also relatively higher as compared to those inside or outside the shelter.However,the parameters related to fruit quality had no significant difference among different treatments.Based on the findings,the comprehensive preventive and curative integrated management module of kiwi canker disease was development for sustainable kiwifruit production. |
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