Study On The Conidia Dispersal And The Disease Dynamics Of Apple Tree Canker Caused By Valsa Mali In Shaanxi

Shaanxi is the main apple-producing areas in China, with cultivated area of9.6802×106hectare and yield of9.6509×106ton in2012. With the biggest areas and largest yields in China,apple industry is one of the most important industries in Shaanxi to enhance agriculturalefficiency and farmer income. However, apple valsa canker, a severe stem disease, caused byValsa mali Mayabe et Yamada, has became a threaten to apple industrial development. Applecanker disease often lead to stem rots, death of twigs and limbs, and even mortality of thewhole tree when severely infected. At present, it is still controversial on the optimal controlperiod, because cultivars and cultivation mode have changed and the epidemic information islimited. Thus, disease management become difficult; especially the passive measure ofscraping the scars, which was commonly used, couldn’t achieve a perfect effect. The epidemicrules is the basis for establish the effective disease control strategies. Consequently, thisresearch has investigated the dynamics of the apple tree canker lesion, the lesion year-roundexpansion dynamics, conidia horn releasing and the conidia dispersal dynamics at specificlocations and periods for the aim to help making up control methods. We also studied thecorrelation between the bark nutrients and the development of apple canker. The main resultsare as follows.1. New scars appeared every month, and the peak period was in November, December,January and February. The dormant period was more favorable for infection; the number ofnew infections in dormant period was significantly higher than that in growing season.2. The canker lesion of apple tree could develop all around the year, and expanded morerapidly from March to May. The most favorable month of lesion expansion was April. Growthrate of lesions were fasted during spring, followed by summer and winter, and slowest inautumn.3. Condia horn could be found all around the year in the field, and the peak periodappears in spring. Its release was mainly affected by rain fall and relative humidity, but not byair temperature.4. The conidia can disperse during the whole year in the field, and the peak period isfrom February to June, of which flowering April with the greatest amount of conidia. The conidia could disperse within the height of canopy during the whole year, the number ofconidia is dispersed0.5m~1.5m above the ground is more than that of2m above. At theheight of2.5m, the number of the conidia dispersed the least.5. Based on the results of investigation, it is verified that the critical period for theprevention of apple valsa canker is June to September. We should smeare and sprayfungicides to reduce the new scars on the tree trunk at June to September, and scrape thecanker lesion.6. The results showed that the content of C/N, soluble carbohydrate and water are notsignificant difference between the health tree branches and the diseased tree branches. It isconfirmed that the occurrence of apple valsa canker didn’t affect the content of C/N, solublecarbohydrate, water in the branches of the apple tree.