Preliminary Study On The Resistance Mechanism Of Kiwifruit Against Corynespora Cassiicola

Kiwifruit brown leaf spot is the second most important disease of kiwifruit in Sichuan Province after kiwifruit bacterial canker,which mainly damages leaves and seriously affects the quality and yield.Currently,the chemical control is believed to be the main method to prevent and control brown leaf spot disease for optimum production;but it posed resistance against pesticides,accumulated pesticide residues and other hazards.Therefore,breeding and utilizing disease-resistant varieties is the most useful and cost-effective measure.Our study assessed the resistance characteristics of kiwifruit leaf tissue structureand the host resistance response induced by Corynespora cassiicola.Based on the resistance screening of kiwifruit varieties against brown leaf spot disease,Hongyang was found highly susceptible,where as Jinyanas resistant and Longshan as high resistant varieties.The main objective of current study was to screen out the structural,physiological and biochemical resistance of kiwifruit varieties against brown spot disease,and to provide a theoretical basis for further exploration of the interaction mechanism between kiwifruit and brown spot disease.The main results so far achieved are as follows:The observation of leaf tissue structure showed that the resistance varieties were significantly lower than the susceptible varieties in terms of leaf stomatal density,sponge tissue thickness and leaf thickness,and the correlation coefficients with brown spot disease were 0.668,0.892 and 0.990,respectively.The difference in the waxes content,the thickness of the upper and lower epidermis,and the thickness of the palisade tissue were not significant.The results with reference to infection process of C.cassiicola on leaf showed that the resistance varieties had no obvious effect on the germination of spore,but there has an effect on the formation of appressorium and penetration pegs.The observation on spore morphology,anaphylaxis,reactive oxygen species and lignin accumulation on the leaves showed that,the HR response of the resistant varieties Longshan and Jinyan was more intense than that of Hongyang variety.The HR responseappeared in Longshan after 12h of inoculation;while in Hongyang it was observed after 48h of inoculation.The accumulation of H₂O₂and lignin observed in all three varieties revealed that in the resistant varieties it was occurred earlier and higher than Hongyang variety.The expression of defense enzymes and disease-resistant genes were detected at different time periods after inoculation.The result showed that PAL,SOD,POD and PPO in Longshan and Jinyan were rapidly activated after inoculation.However,the expression levels of disease-resistant genes PR1,PR4,PR6,β-1-3glucanase and JIHI were increased in different degrees after 48～72h of inoculation,and the expression levels of disease-resistant genes in Longshan were significantly higher than Jinyan and Hongyang.