Studies on shoot growth and flower initiation in apples : A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Horticultural Science in the University of Canterbury

Abstract

In experiments with mature apple trees (Malus domestica Borkh.), cv. Splendour, Granny Smith, Golden Delicious and Red Delicious on MM 106, trained to Lincoln canopy, the effects of proximity to the root bud position and cultivars on shoot growth were studied. Proximity to the root and bud position were the two main factors affecting shoot growth. Most of the large shoots were produced from basal buds on the upper side of the stem. The production of short shoots or spurs in the basal region was mainly from buds on the two sides of the stem and in the apical region from buds on the upper side of the stem. Most of the buds on the lower side, in both regions and on the sides at the distal end, remained dormant and few grew into spurs. Despite slightly delayed bursting, the basal shoots were dominant over the apical shoots due to their higher growth rates and longer period of growth; in fact, they grew almost the entire season. Shoots arising at positions more distant from the centre of the tree had slow growth rates, shorter internodes, more flowers and grew for a very limited period.

Although the general pattern of shoot growth in all cultivars was found to be similar, there were some varietal differences both in the production and distribution of shoots. The ratio of large shoots to small shoots was the highest in Red Delicious followed by Splendour, Granny Smith and Golden Delicious. In Red Delicious, there were few shoots with less than 0.5 cm diameter.

In another experiment, the effect of NAA and IBA on stump sprout control in apples was studied. Both NAA and IBA at 2.0% in lanolin were most effective in controlling sprouting below the pruning cut. In the year of application, IBA was better than NAA in checking shoot regrowth, but in the carry-over effect to the second year, NAA was better than IBA. There was no effect on crop yield.

Suppressing growth of basal shoots on an apple tree by NAA and IBA had no effect on the number of shoots or the total amount of shoot growth in the apical region.