Techniques Of Improving Potassium Nutrition For Protecting Apple From Valsa Canker

Valsa canker of apple is a devastating disease.It is called apple tree "cancer",which seriously restricts the sustainable development of China’s apple industry.The occurrence of the disease is closely related to the health degree of the tree.Based on the preliminary study of our laboratory,it was found that the potassium content of the tree can affect the health level of the apple tree,thus affecting the occurrence of Valsa canker.The potassium content of apple orchard is generally low in China.On the one hand,it is related to the un-enough usages of potassium fertilizer.In addition,low soil organic matter,drought stress and other factors affect the absorption and utilization of potassium fertilizer by apple trees.This study is intended to explore the effective fertilization techniques to improve the content of potassium in dormant period,in order to ensure that tree potassium keeps at the level of disease resistance in the peak of canker occurrence in winter and early spring.In addition,the possible resisitant mechanism of potassium for Valsa canker was analysed through the relationship between potassium content and metabolites on apple callus.The results of this study are as follows:1.Through the mixed application of DP03-4 agent and different fertilizers,the effects of cpmbined fertilizers on the efficiency of potassium fertilizer absorption in trees were explored.It is concluded that all the combination by DP03-4 agent+humic acid,DP03-4 agent +fulvic acid granule,DP03-4 agent + humic acid + sheep manure,DP03-4 agent+ mineral fertilizer,DP03-4 could improve the potassium content of branches.Compared with other combinations,the treatment of DP03-4 agent + fulvic acid,DP03-4 agent +humic acid + could promote the main branch length growth,,the number of new branches.The effect of DP03-4 agent+ humic acid treatment was significantly higher than that of others.2.The effects on potassium contents were analysed by fertilizing in the autumn as the roots in the second developing stage,the results showed that the potassium contents of the tree increased in different degrees after applying different amounts of potassium fertilizer in mid-September.The best result was achieved when applying K2SO4 in 200kg/mu.The potassium content of this treatment of tree decreased in February and then rised again in Marchwhich made the the potassium content higher than the minimum requirement(7.5g/kg)for disease resistance.The application of an appropriate amount of potassium fertilizer is an effective technique to prevent the occurrence of Valsa canker when fertilizing in midSeptember.3.The effects on potassium contents were analysed by irrigating DP03-4 agent around rhizosphere.It was concluded that the potassium content of leaves increased by 13.49% in August and branches increased by 12.78% in April compared with that of not irrigation DP03-4 agent.The results showed that the root irrigation DP03-4 agent around the rhizosphere could effectively improve the potassium content of the branches,and could be used as an adjuvant measure.4.The metabolites of callus at different potassium levels were analyzed by means of liquid chromatography,the data were processed by principal component analysis(PCA)and orthogonal partial least squares discriminant analysis(OPLS-DA).The results shown that 159 metabolites that identified in callus,including 81 basic metabolites,15 terpenoids,18 flavonoids,39 phenylpropanoids and 6 alkaloids.There were significant differences between high and low potassium treatments and inoculated and non-inoculated treatments,and 34 compounds significantly up-regulated under high potassium,including 15 basic metabolites,15 phenylpropanoids,2 flavonoids and 2 terpenoids;and 22 compounds significantly upregulated under high potassium inoculation,including 12 basic metabolites,6 phenylpropane,2 flavonoids and 2 terpenoids;and 12 compounds significantly up-regulated under low potassium inoculation,including 3 basic metabolites,4 phenylpropane metabolites,1flavonoid,3 terpenoids and 1 alkaloid.These results show that substances with potential antimicrobial activity such as flavonoids and Phenylpropanes expressed more under high potassium and high potassium inoculation conditions,which may play an important role in disease resistance.