Factors affecting rooting of in vitro shoots 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.