Formation of Graft Union in Pear: A Histological Study by Using Light Microscopy

Abstract

This research was carried out at the Experimental Farm of the University of Agricultural Sciences and Veterinary Medicine Iasi, Romania during 2008-2010. The anatomical structure of the graft union in heterograft combinations of four pear variety scions on quince rootstock was studied. Tissue samples were taken from graft unions six to twelve months after grafting and first fixed in ethyl alcohol then in formalin/glacial acetic acid solution. Observations were made of the callus tissue between rootstock and scion, the necrotic layers that were formed, the formation of new cambium tissue between rootstock and scion, cambial continuity and the formation of new vascular tissues in the cambium. New cambium, xylem and phloem tissues were formed early in the region of the graft union but a longer time was needed for continuous connections to form within the cambium. Abnormalities were seen within the area of the graft union with some of the scion/rootstock combinations indicating incompatibility for these particular graft combinations. The results provide the possibility of applying an early selection method that will help to predict the future compatibility level of a specific scion/rootstock combination long before any external symptoms could be observed.