The Resistance Of Sichuan Walnut Varieties(Clones) To Walnut Blight And The Correlation Between Leaf Structure And Walnut Blight

As an important economic tree species,walnuts have been greatly promoted in the hills and mountains in Sichuan Province.The walnut planting area and annual output in Sichuan province are among the top in China.However,With the continuous expansion of walnut planting area and the improvement of intensive cultivation,the problem of pests and diseases has become increasingly serious.Due to the influence of high temperature and high humidity weather conditions in Sichuan,the appearance of walnut blight was more serious,which has caused serious impact on the expansion of the walnut industry in our province.Breeding and cultivation of resistant varieties is particularly urgent.Therefore,in this study,18 walnut varieties(clones)with different diseases were selected in Sichuan.Resistance evaluation was conducted based on the incidence of pathogens after inoculation with different species,and high resistance varieties were selected.The relationship between leaf morphological structure and resistance to walnut blight was debated.The results as following:(1)Through the isolation and purification of pathogenic bacteria from diseased leaves and diseased fruits collected from walnut bases and walnut groves in Sichuan Province,and through traditional morphological and molecular identification,it was initially showed that the pathogen of bacterial black spot of walnut in Sichuan area belonged to Xanthomonas arboricola.(2)Through artificially inoculating the pathogens of locally isolated walnut blight disease,the 18 main walnut varieties(clones)collected in Sichuan were identified for resistance.It turned out that there was an observably difference in disease resistance among the walnut varieties.The incidence of in detached leaf inoculation changed from37.07% to 75.44%,and the disease index changed from 23.44% to 57.42%.The disease resistance results is 86,91,Qingxiang,Chuanzao No.2 are with high-resistance;200,92,and 199 are resistant clones;64,Shuoxing,Chuanzao No.1,65,and 71 are with moderate-resistant;100,Panhe 1 No.1 and Shujiang No.1 are susceptible varieties.Yanyuanzao and Xiangling are highly susceptible varieties.(3)The blotting method and paraffin section method were applied to the walnut leaves of different disease resistance types to learn the relationship between the morphological structure of leaf and disease resistance of walnut blight.It turned out that: the stomatal length and stomatal density were significant inverse correlation with the disease resistance of walnut blight.The longer epidermis stomata and the higher the densities of the walnut leaves,the worse the disease resistance of the plants.On the contrary,the walnut varieties with high resistance had a small number of stomata and shorter epidermis stomata,which indicating that the length and density of stomata affect the speed and number of pathogens invading the varieties;The ratio of palisade tissue to spongy parenchyma was significant positively correlated with the disease resistance of black spot,that is,the greater the ratio of palisade tissue to spongy tissue,the more resistant the varieties,indicating that the ratio of palisade tissue and sponge parenchyma was greater,and the more palisade tissue was developed,the more spongy parenchyma cells became tighter,the more difficult the pathogens to invade and expand;The rest of the measured leaf structure indicates that:There were no significant correlations between wax content,stomatal width,stomatal area,leaf epidermis and leaf thickness,spongy tissue thickness,thickness of palisade tissue,thickness of stratum corneum,cell structure compactness,cell structure porosity,and disease resistance of varieties.