Preliminary Screening Of Germplasm Resources Against Apple Vasal Canker And Study On The Resistance Mechanism

Apple Valsa canker,widespread in China,has always become constant threat as a serious disease for the apple yield and quality in the apple industry.Ascomycete Valsa mali is the main character in Apple Valsa canker,which brings severe branches canker disease,eventually leading to the death of the whole orchard.At present,the prevention and control of disease is mainly to strengthen the orchard management and chemical and biological control agents.Now,the most cost-effective way to control canker is developing resistant germplasm resources,which has been a great significance to solve the harm of apple valsa canker.China is an extremely rich area of apple germplasm resources and also one of the birthplace.Therefore,the evaluation of the resistance of apple germplasm resource would be a good conditions.More and more research suggests that in the process of plant disease resistance,the expression of pathogenesis-related enzymatic and genes activity may change,which would provide a basis for reasonable application.In this study,we inoculated the one-year-old shoots of 40 apple varieties and 60 stocks with the V.mali wild isolate 03-8 of high pathogenicity to determine the resistant of these apple germplasm resources for V.mali.With the strongest resistant and susceptible apple germplasm resources as materials,using the V.mali.wild isolate 03-8 and blank PDA as treatments and controls.The changes of resistance to disease-related enzymes and the expression of disease-related genes were detected by spectrophotometer and qRT-PCR.The main results were as follows:1.40 apple cultivars all susceptible,immune or highly resistance cultivars were not found.After training for 3 days,the lesion length of Changfu No.2,Shouhong,Anqicao,H2,Golden Delicious,Yellow Jonagold,Liquan Fuji spur,Beauty Gala,Feng Fuji and Pink Lady exceeded 25 mm,clustered into a class for susceptible varieties,and the lesion length of Changfu No.2 was the largest,reached 29.58mm;The lesion length of Fuji spur,Apple A,Shenyangnongda,Aijiaxiang,Tsugaru and Junma were less than 20 mm,clustered into a class,for the disease resistance cultivars,and the Fuji spur lesion length was the shortest for13.5mm.2.60 apple stocks all susceptible,immune or highly resistance cultivars were not found.After training 3d,the lesion length of Keziaerma,Wild apple No.5 and Kalaaerma werelonger than 30 mm,clustered into a class,for the susceptible stock,and the lesion length of Kalaaerma was the largest,reached 34.16mm;The lesion length of Donghongguo,Taigu precocious Chinese pear-leaved crabapple,Pingyitiancha,Chinese flowering crabapple,Malus toringoi des(Kunming),Medium maturity Rubyfruit,Small yellow-crabapple,Xifu crabapple and Sakura less than 20 mm,clustered into a class,for the disease resistance stock,and the spot length of Donghongguo was the shortest for 13.07 mm.3.The activity of POD,SOD,CAT,PPO of resistance and susceptible apple germplasm resources began to increase after inoculation of V.mali 03-8,which showed the trend of increasing first and then descending.The peak appeared at day 2d,3d or 4 d after inoculation.Both of which were much higher than those of the blank PDA inoculated.The activities of POD,SOD,CAT and PPO of resistance cultivar Fuji spur were significantly higher than those of the susceptible cultivar Changfu No.2.The peak of enzyme activity of resistant cultivars was 1.29,1.13,1.96 and 1.15 fold higher than that of susceptible cultivars.The activities of POD,SOD,CAT and PPO of resistance stock Donghongguo were significantly higher than those of the susceptible stock Kalaaerma.The peak of enzyme activity of diseased rootstocks was 1.03,1.15,1.36 and 1.18 fold of the peak of susceptible stock.4.The expression of PDF1,NPR1,PR1,PR2 and PR4 of resistance and susceptible apple germplasm resources began to up-regulate after inoculation of V.mali 03-8,which showed the expression trend of rise first and then decline.the peak appeared at 24 h,36h or48 h after inoculation.The expression levels of PDF1,NPR1,PR1,PR2 and PR4 of resistance cultivar Fuji spur were higher than those of the susceptible cultivar Changfu NO.2.The peak values of the resistant cultivar were 1.52,2.04,1.66,1.33 and 1.41 fold higher than those of susceptible cultivar.The expression levels of PDF1,NPR1,PR1,PR2 and PR4 of resistance stock Donghongguo were higher than those of the susceptible stock Kalaaerma.The peak values of the resistant stock were 3.43,4.43,1.91,2.57 and 1.10 fold higher than those of susceptible stock.In summary,there were some differences in the resistance of apple germplasm resources.The activities of POD,SOD,CAT,PPO and the expression of gene PDF1,NPR1,PR1,PR2 and PR4 were closely related to disease resistance.The activities of enzyme and the up-regulation of gene of resistance cultivars and stocks were higher than those of susceptible cultivars and stocks.