Identify Of Resistance To Canker In Citrus Germplasm Resources And Analysis Orah Transcriptome Response To Canker

Citrus canker is one of the important diseases of citrus.It is very important to study the resistance mechanism of citrus canker and to screen resistant resources.In this study,Resistance to citrus canker,stoma density,palisade tissue thickness,MDA content and PPO activity of 30 citrus germplasm resources were measured,and the relationship between leaf structure,physiological and biochemical substances and resistance was tested.72 seedlings of Orah were identified for resistance to citrus canker,and the transcriptome of Orah which response to pathogen invasion were analyzed.The responses and Interaction of Orah and different resistant resources to Xanthomonas Campestris PV.Citri were compared.The main findings are as follows:(1)According to the results of in vitro acupuncture inoculation,30 citrus germplasm resources were classified by resistance.Among them: Huapi Kumquat,Jindou,Jinzao,Yangshuo Kumquat and Changshou Kumquat were super resistant varieties.Jianyang Tangelo,tetraploid Kumquat and M-14 were high resistant varieties,and Guangzhou lemon,perfume lemon,white flower lemon,M-6,M-8,M-11,M-13,M-15 were medium resistant varieties.Guiyou1,Vietnamese Pomelo,hybrid lemon,M-2,M-3,M-5,M-7,M-9,M-10,M-12,M-16 were susceptible varieties,while Orah,M-1 and M-4 were super susceptible varieties.(2)In 30 citrus germplasm,leaf thickness,spongy tissue,epidermis,subcortex,stomatal length,stomatal width,stomatal area had non-significant correlation with resistance to canker disease.Stomatal density was significantly negatively correlated with resistance to citrus canker,and palisade tissue thickness,wax content was significantly positively correlated with resistance.(3)Resistance to citrus canker disease did not significantly relate to the content of soluble protein in healthy leaves,but it had significant negative correlation with MDA content and extremely significant positive correlation with POD,PPO and SOD activity.After inoculation,the activities of POD and SOD,the activities of PPO and the contents of MDA were significantly negatively correlated with the resistance of citrus canker.(4)The resistance of 72 Orah’s seedlings to citrus canker was identified.WG-31 showed stable resistance to canker.(5)After soaking inoculation,the stomata of the resistant varieties continued to close,and the stomata of the susceptible varieties re-opened after closing,and the number of pathogen invading into the leaves of the resistant varieties was significantly less than that of the susceptible varieties.(6)Susceptible varieties contained more factors that could promote exopolysaccharide production by Xanthomonas Campestris PV.Citri than resistant varieties,and resistant varieties induced by Xanthomonas Campestris PV.Citri could produce substances that would inhibition of bacterial growth.(7)There were 374 different expressed genes at 2d,4d,6d and 8d after the Orah’s leaves being invaded by Xanthomonas Campestris PV.Citri 61 genes among them were up-regulated genes and 313 were down-regulated genes.The enrichment analysis of the GO gene in each stage was mainly focused on the biological process,and the KEGG enrichment analysis was mainly focused on the metabolic pathways about disease resistance like biosynthesis of secondary metabolites and the interaction between plant and pathogen.The results showed that the resistance of citrus germplasm to canker disease was related to leaf structure,physiological and biochemical contents or activities.After being invaded by Xanthomonas Campestris PV.Citri citrus plants would show a series of complex responses and had interaction with Xanthomonas Campestris PV.Citri.