Comparative studies on physiological and morphological features of bearing and non-bearing spurs of the apple tree. I. Changes in starch content during growth

SummaryIn four successive years the amount of starch found by enzymic and microscopic methods was significantly larger in non-bearing spurs than in fruit-bearing ones of the biennial cropping cultivar Landsberger Reinette. Every year a dramatic fall in the starch content was observed in the fruit-bearing spurs at the end of June between the 5th and 6th week after full bloom. Applying foliar sprays to on-year trees of succinic acid-2,2-dimethylhydrazide (aminozide) and naphthaleneacetic acid (NAA) caused cessation of growth accompanied by a significant increase in the spur starch content despite the presence of fruits. The flowering of the treated trees was doubled. Gibberellic acid (GA3) applied to off-year trees reduced the starch level in their spurs. It is concluded that the starch content in spurs is lowered by hormones supplied by developing seeds. Hence a high starch content cannot be regarded as a direct cause of flower initiation but only as an excellent and rapid indicator of the direction of metabolic processes resulting from low amounts of auxin and gibberellins in the surrounding tissues.