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Hazelnut is one of the four famous tree nuts in the world. While hybrid hazelnut (Corylus heterophylla×C. avellana) is the major cultivar planted in China, the other parts of the world that grow hazelnuts are characterized by planting European hazelnut (C. avellana L.). Although hybrid hazelnut can withstand a low temperature below -30℃to-35℃in winter, shoot shrivelling in Liaoning, Shanxi, and Beijing has seriously threatened the extension and industrial development of this crop. To make matters worse, no report has been found on the cause or control technique of shoot shriveling to date. Therefore, this thesis paper is attempting to fill in the gap by focusing on water content of the shoot, and applying the most effective protectant in due time. In so doing the the tolerance capacity to shoot shrivelling in 18 clones of hybrid hazelnut was determined. The main results are as follows:1, The cause of shoot shrivelling of hybrid hazelnut lies in the fact that the branch lost too much water during dormancy. When the shoot water content fell to the critical moisture content, the shoot shriveled, and it was not freeze injury that led to shoot shrielling.2, The time when shoot shrieveling occurred differed with geoclimatic regions. InChangping district of Beijing, shoot shrivelling occurred from early February to late February, whereas in Fuxin of Liaoning Province, this was not found until the last ten days of February to the first ten days of March.3, The performance of the tested 18 hazelnut clones were studied to grade their ability to stand against shoot shriveling in winter, and four groups were designated to them according to the results of cluster analysis. The rankings showed that the group with the strongest tolerance included Dawei, B-3, B-21,83-33,84-72 and 81-9, followed by the group including 84-48,81-23,85-127,84-237 and 84-1; 82-11,84-545 and Liaozhen 3 fell into the third group with weak tolerance, and the group with the weakest tolerance comprised 84-572,84-402,84-69 and Liaozhen 1.4, In Beijing, of the 18 clones of hybrid hazelnuts, the critical water content of shoots in 82-11,84-1,84-237, Liaozhen 1,81-23,84-69,84-72,84-402,84-572, and B-21 ranged from 35%-30%. The study of the relationship of water content with shoot shriveling showed that the critical water capacity in different hybrid hazelnuts varied, with most clones between 35% and 30%, and the clones B-3,83-33 and 84-48 over 35%, but Dawei,84-545, Liaozhen 3,85-127 and 81-9 was lower than 30%. There was a high relationship between the critical water capacity and shoot shrivelling resistance, but the critical water concentration of shoot shriveling was not the only factor to cause shriveling of the shoot.5, In the dormant period, the daily cumulative amount of sap flow showed a "down-up" trend, and shoot shrivelling occurred when sap flow fell into the lowest. Branch water content in different hybrid hazelnuts varied, which is significantly in positive correlation with the shoot shrivelling resistance capacity. the absolute content of soluble sugar or soluble protein of branches was not definitely responsible for shoot shrivelling resistance capacity, but there was a high relationship between the rangeability of soluble protein and shoot shrivelling resistance capacity. Electrolyte leakage and electric resistance value were in significant negative correlation with shoot shrivelling resistance capacity. Branches lenticel density or size was not correlated with branch water content, but lenticels surface area ratio of total branches played an important role in the resistance capacity to shoot shrivelling.6, Spraying twice repellant at the beginning time and middle time of the critical period of shoot shrivelling proved to be the effective method to protect hybrid hzalenut from suffering from shoot shriveling. The best repellant is 100 times palmityl alcohol. When planning to establish an orchard of hybrid hazelnut in a dry area, one is recommended to use cultivars that are tolerant to shoot shrivlling to gurantee success.
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