Economic Traits of Special Nut-Processed Cultivars of Ping’ou Hybrid Hazelnuts (Corylus heterophylla×C. avellana) Correlations of the Nut and Catkin Quantity Properties of Corylus heterophylla×C.avellana Genetic Analysis of Nut Traits on Tester Strain of Hybrid Hazelnuts (Corylus heterophylla × C. avellana) A Micro-propagation Technique of Corylus heterophylla×C.avellana