Factors affecting rooting ofin vitroshoots of walnut cultivars

SummaryFactors affecting the rooting of in vitro shoots were investigated using precocious walnut (Juglans regia L.) cv. Xinzaofeng. In vitro sub-culture was the most important step to achieve rooting of the shoots. Rooting of shoots was markedly affected by the method of induction, 3-indole-butyric acid (IBA) concentrations, light conditions, as well as shoot quality. Rooting rates of ≥ 75.4% were obtained with an optimised rooting protocol in which vigorous shoots were sub-cultured 45-times at 20 d intervals. These shoots appeared tender, with small leaves. A transfer method of root induction was applied and shoots were first induced on a semi-solidified, diluted Walnut Specific Medium (1/4 DKW) with 25 µM IBA in the dark for 12 d at 25° ± 3°C, then cultured on semi-solidified 1/4 DKW medium plus vermiculite, without IBA, with a 16 h photoperiod (53 µmol m–2 s–1). This protocol was extended to five other walnut cultivars, and rooting rates of ≥ 60.5% were achieved in all cases.