| Apple canker is one of the most common and serious diseases in China.China’s apple industry is huge,with a planting area of 2.0717 million hectares and a total yield of 39.235 million tons,however,the yield per hectare is only 18.94 tons.Due to the diversity of the infection way of apple canker’ s pathogen is and the disease can cause great damage to apple tree,even totally destroy the apple orchard.The occurrence of apple canker is affected by many factors,including seedlings,climatic conditions,cultivation,disease prevention,plant resistance and other factors.The growth vigor of the tree and its nutrient content are important factors which affecting plant resistance to apple canker disease.Little is known about The Correlation between growth vigor and canker disease resistance.Many studies suggest that increasing growth vigor can improve disease resistance.Based on previous studies,this study analyzed the relationship between the growth vigor of branches,total soluble sugar,starch content,trace elements(Zn,Mn,and Cu)and the occurrence of apple tree canker.The results are shown as follows.1.The content of various nutrients and the incidence of canker in the branch ages 1-10 years were assessed.The results indicated that the incidence of canker increased with branches ages;The content of all 7 elements(N,P,Mg,Zn,Cu,Mn and Fe)had significant negative correlations with branch age,the correlation coefficient were-0.939,-0.754,-0.931,-0.819,-0.872,-0.819,-0.926,respectively;while calcium content showed a significant positive correlation,the coefficient was 0.911;the content of soluble sugar,starch,and K had no significant correlation with branch age.Most of the nutrients in aged branches are less than the younger ones.The reduction of nutrient content results in lower growth vigor,cell viability,resistance and healing ability and higher morbidity of aged branches.2.The length of spring shoots,middle internodes and autumn shoots,and quantity of canker scars in annual branches were measured,and their correlations were also analyzed.The data showed that no scars on the branch was detectedonly if the length of the spring shoot is 23.4 cm.Correlation analysis between the length of spring shoots and number of scars was performed.When the spring shoot length was higher than 23.4 cm,the spring shoot length was significantly positively correlated with the number of scars,and the correlation coefficient was 0.277;the correlation was not significant if the length was less than 23.4 cm.Similarly,when the length of the middle internode was greater than 2.77 cm,the length of the middle internode had a significant positive correlation with the number of scars,with a correlation coefficient of 0.341;when the length was less than 2.77 cm,the length of the middle internode was significantly positively correlated with the number of scars,and the correlation coefficient is-0.171.The tree with the shortest autumn shoot length was the least affected.The correlation analysis between the autumn shoot length and the number of scars showed that the length of the autumn shoot had a significant positive correlation with the number of scars,and the correlation coefficient is 0.238.The conclusions have proved that weak or over-prosperous tree have a negative impact on the disease resistance.When the branch was poor growth or excessive growth,the tree will lose resistance with diseases,and had a more serious occurrence of canker,so a moderate growth is the best for trees.3.After analyzed the correlation between nutrient element content and the canker disease in the orchards in multiple regions,we found that the content of Mg and Mn in the annual branches was significantly positively correlated with the number of canker scars,and the correlation coefficients were 0.278 and 0.405,respectively;The content of K had a significant negative correlation with the number of scars,the correlation coefficient was-0.268;the soluble sugar has a significant positive correlation with the incidence of canker;the content of starch,Zn,Fe has no obvious correlation with the occurrence of canker.Stepwise regression analysis showed that the optimal regression equation was y=-2.764+37.632 Mg-3.923 K+0.281 Mn,and indicated that K has a certain inhibitory effect on the occurrence and continued deterioration of canker disease,and additional K fertilizer in production has a positive effect on preventing and controlling canker disease.The increase in the content of Mg and Mn may lead to an increase in the disease degree of the tree.By analyzing the correlation between the ratios of K,Mg,and Mn,which are the most influential elements,and the number of scars in the tree,it was concluded that ratios of K/Mg,Mn/Mg,Mn/K and occurrence of canker disease was significantly related.The regression equation(y=3.221-0.551×(K/Mg)+0.031×(Mn/Mg))showed that the correlation test results of K/Mg,Mn/Mg and the number of scars were extremely significant.4.After surveying and comparing the cultivation and management methods of two adjacent orchards with different levels of canker disease,it was found that reasonable plant row spacing,good ventilation and light condition,tree shaping,reasonable fertilizer and water management,and disease prevention can greatly reduce the occurrence and spread of canker disease,thereby increasing orchard yield and high-quality fruit rate.In addition,it was also found that the orchard applicated with chicken manure which have high potassium content ghad higher resistance to canker disease.The result also indicated that K has played an important role in the prevention of apple tree canker.The occurrence of apple tree canker is related to the growth vigor and the content of several nutrients in the tree.The aged branch had weak the growth vigor and the occurrence of canker disease was higher.However,the prevention of canker disease cannot blindly enhance the growth of the tree.Excessive growth or poor growth of the tree will cause the occurrence and aggravation of canker.Therefore,a balanced and robust tree can achieve good prevention of disease.The increase of K can inhibit the occurrence of canker,and the increase of Mg and Mn may aggravate the disease.At the same time,strict scraping and bridging and other methods can also prevent the recurrence and deterioration of canker disease.Hence,monitoring the nutrient status of the tree and supplementing nutrients according to the nutrient statuscan greatly reduce the damage of apple canker disease. |
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