Morphological and Anatomical Investigations on in Vitro Micrografts of OHxF 333 / Pyrus elaeagrifolia Interstock / Rootstock Combination in Pears

In this study, possibility of creating a specific interstock / rootstock combination to obtain a clonal, semi dwarf, composite pear rootstock tolerant to various stresses by micrografting was investigated. In vitro shoots of ‘Old Home x Farmingdale 333’ (Pyrus communis L.) which is a clonal semi dwarf pear rootstock resistant to fireblight and pear decline was used as interstock, and in vitro Pyrus elaeagrifolia Pallas seedlings known as tolerant to Fe-chlorosis, salinity and drought stresses was used as rootstock. Cleft grafting was applied in micrografts. Grafted seedlings were cultured on Murashige and Skoog basal medium with ½ strength of macronutrients for 8 weeks under white fluorescent light for 16 h day^-1. Cultures, except the control, received complete darkness either 1 or 2 weeks at the beginning of incubation. Graft take success in the control treatment was significantly higher (97.9%) than darkness treatments of 1 or 2 weeks (90.5% and 82.5%, respectively). Ultrastructural observations with transmission electron microscope revealed that dividing cambialinitials reached to 2-3 layers, and new xylem and phloem elements distinctly differentiated in transverse sections of the graft union 8 weeks after micrografting in the control and darkness treatments. The results indicated a successful graft union formation.