Enhancing budbreak and axillary shoot development of 'M.9' apple rootstock during the early period of stool-bed establishment

Abstract

During the early period of establishment, productivity of newly planted stool beds is often limited because a low proportion of axillary buds break along the rootstock stem, despite these buds being anatomically well developed. Using newly established stool beds of the apple rootstock 'M.9', we applied thidiazuron (TDZ; 1000 mg L -1) on to the rootstock stem at budbreak (on 15 September 2005) or 2 weeks later to ascertain whether axillary budbreak along the rootstock stem could be enhanced. Subsequently, foliar sprays of gibberellins (GA 4+7; 400 mg L -1) were applied to determine whether elongation of the resultant axillary shoots could be increased. TDZ applied at budbreak or 2 weeks later increased the percentage of axillary buds that broke to form shoots, with more than 80% of buds breaking on TDZ-treated rootstocks compared with 41% for the untreated control. The elongation growth of newly produced shoots in response to foliar application of GA 4+7 was pronounced for the TDZ-treated rootstock stems. TDZ painted on to the rootstock stems at budbreak or 2 weeks later increased the yield of stool shoots per metre length of new stool bed from approximately 18 in the control to c.30 with GA 4+7. Paint application of TDZ (1000 mg L -1) followed by foliar application of GA 4+7 (400 mg L -1) can increase stool shoot yield in newly planted stool beds. © 2011 The Royal Society of New Zealand.