Journal APS Oct 2017

J ournal of the A merican P omological S ociety

220

Journal of the American Pomological Society 71(4): 220-225 2017

The Relationship Between Environmental Factors and Rootstock Growth Stage with Graft Success in Walnut B urak A ky Ü z 1 and Ü mit S erdar Additional index words: temperature, Juglans regia L., outdoor grafting, English Walnut Abstract  The aim of this study was to determine the influence of environmental factors and rootstock growth stage on graft success. The experiment was conducted during 2012 and 2013 at the Black Sea Agricultural Research Institute of Samsun, Turkey. The whip-and-tongue method was used to graft ‘Chandler’ ( J. regia ) scion wood onto one-yr-old English walnut seedlings ( Juglans regia L.). A factorial experiment with two years, two nursery conditions (open field and greenhouse with 50% shade) and four grafting times (15 March, 5 April, 25 April and 15 May) was performed to evaluate factors affecting grafting success. Graft success ranged from 18.3 to 100 % depending on nursery conditions, grafting time and year. Best graft success was obtained between the period of bud burst and about 15 cm shoot growth of rootstocks. Depending on the year, graft success was negatively correlated with minimum and mean temperature (p<0.01). The growth level of rootstocks was a useful indicator to initiate grafting for walnut under outdoor conditions.

 Walnut ( Juglans spp.) is one of the most important tree nuts that is grown nearly around the world. World’s walnut production is 3,458,046 tones (FAOSTAT, 2016), but compared to the tree density fruit production is lower than expected (Stanisavljevic and Mitrovic, 1997) due to the planting of seedlings or cultivars that produce low yields. Walnut can be propagated by using generative or vegetative methods. Vegetative propagation of English walnut ( Juglans regia L.) is considered more difficult than other fruit and nut trees (Gandev, 2007). Rooting of walnut is limited by physiological conditions such as the presence of high concentrations of phenolic compounds and their oxidation by wounding (Eris and Barut, 1988; Rongting and Pinghai, 1993).  The most common propagation method in walnut is grafting. Grafting of walnut needs more care due to the low rate of callus formation when compared to other fruits (Kruniyuki and Fordi, 1985; Coggeshall and Beineke, 1997; Akça, 2005; Ahmed et al., 2012). Grafting can be performed both

indoors (greenhouse, etc.) and outdoors (field, forest, orchard, etc.). Optimal environmental conditions, grafting method and grafting times important for maximum graft success of walnut depending on a particular region (Ahmed et al., 2012). Success is affected by sap production (“bleeding”), temperature, relative humidity, quality and growth stage of scion and rootstocks, and time of cutting the scion wood (Kuniyuki and Forde, 1985; Rongting and Pinghai, 1993; Gandev, 2007; Rezaee and Vahdati, 2008).  There are many studies describing the suitable method and time of grafting walnut (Ahmed et al, 2012; Erturk, 2013; Mir and Kumar, 2011; Stanisavljevic and Mitrovic, 1997) and the whip-tongue grafting method was reported to be the most successful method (Achim and Botu, 2001; Ozkan and Gumus, 2001; Asghar et al., 2006).  Environmental conditions affect grafting success for all fruit trees. Researchers have shown that walnut does not produce callus below 20°C and the optimum temperature for callus formation is 25-27°C (Erdogan, 2006;

1 Corresponding author: Phone: +905447232313 E-mail address: burakakyuz87@gmail.com Department of Horticulture, Faculty of Agriculture, University of Ondokuz Mayis, Samsun, Turkey