Effect Of Nitrogen And Potassium Content On Occurrence Of Apple Valsa Canker

Valsa canker is one of the most destructive diseases of apple tree, and is a severe threat to the economic viability of apple production. The pathogen usually considered to be weakly pathogenic, and it infects in the wounds of weak trees but not in those of vigorous trees. Nitrogen(N) and potassium(K) are the essential nutrients of apple tree, which significantly impacting the tree vigor. Our earlier studies have shown that Valsa canker is closely related to the K and N/K of apple tree. On that basis, our object of this study was to explore the influence of N and K on Valsa canker, find a effective method to improve the K content for apple tree, and then provided an effective method and a theoretical basis for the control of Valsa canker. The results as follows:1. Fertilization experiments shown that root irrigation different K level fertilizer(KO) 340 g, 255 g, 170 g, 85 g respectively, could improve the leaf k content for 96%, 76%, 47%, 30% respectively. 540 g potassium fertilizer were applied to the soil around each tree(81 kg/ha), which could improve the leaf K content to 1.25%. The result shown that, for drip irrigation with raised potash application can effectively increase the K content of trees. The K content increased by 25% when spraying 0.1% aqueous solution of potassium dihydrogen phosphate for 8 times.2. We also investigate the effect of different levels of K content on the occurrence of Valsa canker for the growing season and the following spring of apple tree. Leaf potassium content in mid August: reached 1.25%, 1.12%, 0.98%, 0.83% and 0.64%, respectively, then the leaves were inoculated by Valsa. The result showed that the lesion did not occur when leaf potassium content reached 1.25% or 1.12%, while other treatments were onset. It was also found that Valsa lesion did not occur only leaf potassium content reached 1.25% and the lower potassium content, the more severe Valsa canker was. These results indicated that it can effectively control Valsa canker in next spring when leaf potassium content reached 1.25% in early August. So we recommend that the leaf potassium content of 1.25% as the nutritional standards to prevent apple Valsa canker.3. We analyzed the impact of high nitrogen treatment on Valsa canker incidence: we made different high nitrogen content apple tree(> 0.7%) by pot experiment. Branch nitrogen content in early April was 1.05%, 1.40%, 1.99%, and 2.23%, respectively, then the branch were inoculated by Valsa. The result showed that Valsa canker remained heavily occurred under the condition that branch potassium content achieved the recommended content 0.7%. These results indicated that it could promote Valsa canker when the nitrogen content in apple tree was too high. So we recommend that controling nitrogen fertilizer on the premise of effectively improving the potassium content, thereby maintaining the nutrient balance of nitrogen and potassium.4. We observed different potassium content apple tree has an influence on Valsa’s expansion by slicing. The results showed a significant positive correlation between the potassium content and the thickness of the exophylactic periderm. This result explained part of the reason for the host immune resistance to disease in anatomy.