Study On Resistance Of Different Varieties Of Kiwifruit To Blue Mold During Storage

Blue mold is one of the most important diseases causing rot of postharvest kiwifruit.This experiment uses 6 varieties of kiwifruit as materials,including two red heart varieties Hongyang and Qihong,two yellow heart varieties Nongda Jinmi and Jinyan,and two green meat varieties Xuxiang and Hayward.After inoculated with Penicillium expansum,the changes of physicochemical quality,volatile matter and physiological indexes of different varieties of kiwifruit during cold storage were compared and analyzed.And the differences in tissue structure of the peel were observed by scanning electron microscopy.In order to provide theoretical and technical basis for identification and screening of resistant varieties of kiwifruit,combining the physiological and biochemical resistance and tissue structure resistance of fruits,revealing the resistance mechanism of postharvest kiwifruit to blue mold.The main conclusions of this study are as follows:(1)There are differences in the disease resistance of different varieties of kiwifruit to blue mold.The wound-inoculated group of Qihong and Jinyan had earlier onset time and serious disease state,and the disease resistance was poor;Nongda Jinmi and Xuxiang had earlier onset time,but disease state were lighter;Hongyang had a later onset time,but the disease state was more serious;Hayward not only had a later onset time,but also had lighter disease state,so had stronger disease resistance.The overall performance was that the Actinidia chinensis were less resistant to blue mold,while the Actinidia deliciosa were more resistant.(2)Inoculation with Penicillium expansum accelerates the decline in the quality of kiwifruit,which accelerated the decrease in fruit firmness,TA and Vc content,and promoted the increase of SSC.At the same time,the decresce of the brightness L*,the saturation C* and the hue angle h° of the flesh color were accelerated,and the flesh color was darkened and the saturation was lowered.After inoculation with Penicillium expansum,the content of Hexanal,trans-2-hexenal and trans-2-heptenal,which were characteristic flavors of kiwifruit,gradually decreased with the severity of the disease.The contents of volatile substances such as ethanol,3-methyl-1-butanol and 2-methylisoborneol were gradually increased.And alcoholic and musty taste was found in diseased kiwifruit.According to various quality indicators,the inoculation of Penicillium expansum has a serious influence on the quality of Actinidia chinensis Qihong,Nongda Jinmi and Jinyan during storage time,accelerated the quality deterioration.The influence of Hongyang kiwifruit is second,and there was less influence of the Actinidia deliciosa Xuxiang and Hayward.(3)After inoculation with Penicillium expansum,the growth and expansion of pathogens can be resisted through its physiological and biochemical resistance and tissue structure resistance.The kiwifruit improved the biochemical resistance to the blue mold by promoting the synthesis and accumulation of resistance-related substance such as total phenols,flavonoids and lignin in the secondary metabolites and increasing the activities of resistance-related enzymes such as POD,PAL,CHI and GLU.Comprehensive comparison of four resistance-related enzyme activities and three resistance-related substances in six varieties of kiwifruit,found that Actinidia deliciosa Xuxiang and Hayward showed higher biochemical resistance,Actinidia chinensis Hongyang and Nongda Jinmi,Qihong and Jinyan showed lower biochemical resistance.The epidermal tissue structure of the fruit was observed by scanning electron microscopy.It was found that the epidermal structure of Hayward,Xuxiang and Hongyang was more uniform and dense,the cells in the longitudinal section were arranged neatly and with small cell gap,and there was no obvious pore inside the epidermis.And the epidermis of Xu Xiang and Hayward were densely covered with fluff,therefore they had structural characteristics of disease resistance.Qihong and Nongda Jinmi were densely covered with small cracks,and the longitudinal section cells of Nongda jinmi and Jinyan were arranged in disorder without obvious cell contour,therefore they had susceptible tissues structure.(4)In summary,Hayward kiwifruit has a long incubation period after inoculated with Penicillium expansum,with lower incidence,slowly disease spreads and low influence on quality.And Hayward showed higher biochemical resistance with higher activities of resistance-related enzymes and higher contents of resistance-related substance.In addition,it showed higher tissue structure resistance with relatively uniform and dense epidermal tissue structure,so it had strongest resistance to blue mold.The incubation period of Xuxiang kiwifruit after inoculated with Penicillium expansum was relatively short,but the disease spreads slowly,the degree of influence on quality was also small.And the incubation period of Hongyang was longer,but the disease spreads faster,and the effect on quality was more serious than Hayward and Xuxiang.Xuxiang and Hongyang were showed stronger biochemical resistance and tissue structure resistance.There were short incubation period after inoculated with Penicillium expansum of Nongda Jinmi,Qihong and Jinyan Kiwifruit.But the disease spread speed of Nongda Jinmi was relatively slower,showed relatively higher biochemical resistance.Qihong and Jinyan showed rapidly disease expansion rate and showed weak biochemical resistance.After inoculated with Penicillium expansum,Nongda jinmi,Qihong,and Jinyan had more serious influence on quality,and the epidermis structure was loose and scattered,showed weak tissue structure resistance.So they had weak resistance to blue mold.Therefore,it can be obtained that the order of disease resistance after inoculation with Penicillium expansum was Hayward,Xuxiang,Hongyang,Nongda Jinmi,Qihong,Jinyan.