An investigation on mechanisms of blanked nut formation of hazelnut (Corylus heterophylla fisch)
The occurrence of blank nuts is common in Corylus heterophylla Fisch orchards of China. This study was aimed to find the possible mechanisms involved in blank nuts formation in wild C. heterophylla Fisch species. The effects of pollination, defoliation and girdling on fruit production of C. heterophylla Fisch were studied from northern China. The effect of pollination on various aspects of the reproductive output of C. heterophylla Fisch was studied by performing hand pollination, open pollination and no pollination. Different pollination types significantly affected flower cluster set including no flower cluster set produced in no pollination treatment. However, pollination type had no direct effect on nut and kernel traits. Three defoliation treatments (control, 50 and 100% leaf removal) were applied at branch level on 10 trees. Six branches were used per treatment in each tree and half of these branches were girdled (a ring of bark and cambium was removed from the branch base). Leaf removal from ungirdled branches had little effect on pistillate flower cluster set, fruit cluster set and nuts per cluster. However, these variables decreased as the extent of 100% defoliation increased on girdled branches. Defoliation and girdling reduced nut and kernel weight which was the result of a reduction in the kernel weight rather than nut coat reduction. Control of the carbohydrate supply to the reproductive shoots by girdling and defoliation made no difference to nut number and size but the kernel percent and blank nut ratio were highly sensitive to carbohydrate availability. Resource importation not exportation by fruiting branches might be a mechanism to reduce blank nut in this species.
Keywords: Corylus heterophylla Fisch, pollination, defoliation, girdling, blank nut