The Resistance Evaluation And Resistance Mechanism Of Different Kiwifruit Varietiesto Pseudomonas Syringae Pv. Actinidiae

Kiwifruit bacterial canker is mainly caused by Pseudomonas syringae pv.Actinidiae(Psa),which is is a severe threat to kiwifruit production.The disease spreads rapidly,not only in Shaanxi Province,but also in the other kiwifruit production areas have caused serious losses around the world.At present,it mainly relies on chemical pesticides to control kiwifruit bacterial canker,but long-term using pesticides has caused many disadvantages.Some researches has found Psa is resistant to some pesticides.Many scholars believe that the most effective measure to control kiwifruit bacterial canker is to cultivate resistant varieties,but there are a few studies on the disease resistance mechanism of the varieties in Shaanxi.This study evaluated the resistance of 9 common varieties in Shaanxi Province.According to the differences about infection process,the change of defense enzymes activity and the expression of resistance-related genes between resistant and susceptible varieties after inoculation,we can reveal the mechanism of kiwifruit against Psa,and provide theoretical basis for controlling kiwifruit bacterial canker.The main findings obtained are as follows:1.We evaluated nine kiwifruit varieties using quantitative inoculation in vitro,the results showed that there was a significant difference in disease resistance among the varieties,the degree of disease is,Hongyang>Xixua>Huayou,Cuixiang,Jinyan>Yate,Qinmei>Hayward>Xuxiang.The chinesis variety Hongyang(Actinidia chinensis cv.Hongyang)was the first showed symptom(10 d)and had the largest lesion length(15.99cm),therefore,we think it is the most susceptible variety.Compared with the susceptible variety Hongyang,the delicious variety Xuxiang(A.deliciosa cv.Xuxiang)showed the symptom was later than the other varieties(15 d),had the smallest lesions(1.76cm)and the strongest disease resistance,which was significantly better than the other tested varieties.2.The colonization and expansion dynamics of Psa strain M228-GFPuv,that in canes and leaves of the resistant variety Xuxiang and susceptible variety Hongyang were detected.In canes,the symptoms of Hongyang showed early,and the obvious symptoms were observed at 10th day after inoculated with M228-GFPuv.A large amount of Psa could be detected at the range of 0-4 cm,and the maximum amount of Psa was 5.67×10~8 CFU/g.The resistant variety Xuxiang was the latest to show symptoms(15 d),and Psa only existed at the range of 0-1cm,and the maximum amount of Psa was 2.86×10~8 CFU/g.According to the vacuum infiltration of the leaf discs,both Xuxiang and Hongyang showed symptoms at 2th day after inoculation.In Hongyang,the spread of lesions was faster,and the whole leaf disc was covered with Psa at the 6th day.However,the size of disease spot expanded slowly in Xuxiang,and the lesions were no longer expanded after 5th day,the disease spot area only accounted for 10%of the whole leaf disc.After inoculation in veins,the resualts showed that both the fluorescence intensity and expansion distance of Psa reached the maximum at 12th day in Hongyang.The strongest fluorescence intensity of Xuxiang was at 15th day after inoculation and was weaker than that of Hongyang,the expansion range was limited to the vicinity of the inoculation point.3.After quantitative inoculation of kiwifruit in vitro,the changes of peroxidase(POD),phenylalanine ammonialyase(PAL),superoxide dismutase(SOD)and catalase(CAT)activity were measured at different times after inoculation.The defensive enzymes activity of the resistant variety Xuxiang and the susceptible variety Hongyang was not significant difference compared with the control,but the difference about the increase rate of enzymes activity was notable.In canes,the activities of POD and PAL in Xuxiang were significantly higher than that in Hongyang.In Xuxiang,POD and PAL reached peak at the early stage(5d),was 2.81 and 2.56 times of the control,while the reached peak later(20 d)in Hongyang,which was 1.9 and 1.87 times of the control.There was no significant difference in SOD activity between Xuxiang and Hongyang before and after inoculation.The CAT activity of Xuxiang reached the peak before the onset of symptoms,in the late stage of Hongyang,it peaked and was higher than Xuxiang.In the leaves,the four defense enzymes activity of the two varieties were significantly higher than the control,and the peak activity of Xuxiang was earlier than that of Hongyang.The POD and PAL activities of Xuxiang changed significantly,and reached the peak of 3.62 times and 1.80 times of the control at 6th day after inoculation.The peak appeared earlier and the enzyme activity changed more than Hongyang.After inoculation,SOD activity of two varieties showed a trend of continuous increase,and the difference between the two varieties was small.The difference about CAT activity was not notably between Hongyang and Xuxiang,which was 2.37 and 2.26 times of the control respectively.4.The quantitative analysis of defensive enzyme-regulated genes and reported resistance-related genes in kiwifruit canes and leaves by qRT-PCR.The results revealed that all genes in Xuxiang were up-regulated and higher than that in Hongyang.Especially PR1,PR5,PAL and POD,the expression level was significantly up-regulated in the canes and leaves of Xuxiang,while they were down-regulated in Hongyang.And the R genes PRS2and Rpm1 and the PAMP-responsive genes Rboh and CDPK were up-regulated in Xuxiang.The phase corresponds to down-regulated expression in Hongyang,indicating that the expression of these genes plays an important role in the disease resistance of Xuxiang.