Lateral shoot formation and flower-bud formation in apple in the first year after budding as affected by air temperature and exposure to red light

Abstract

Under controlled environment conditions the effect of three air temperatures (16°, 21°, and 26°C) and of low-intensity red light during the night (at 21°C only) on the vegetative development and flower-bud formation of apple trees (cvs Rode Boskoop and Elstar) were evaluated in the first year after budding. Day and night temperatures were the same; soil temperature was 17°C. The vapour pressure deficit of the air was low (about 0.40 kPa at each temperature). Shoot growth increased with increasing temperature especially in the 16-21°C range. The growth effects were mainly reflected in lateral shoot growth. At 16°C lateral growth was poor (in ‘Boskoop’) or almost absent (in ‘Elstar’). At 26°C, lateral shoots was more evenly spread along the main axis than at lower temperatures. Exposure to red light had no effect on growth. Flowering on the main stem and on the lateral shoots were considerably less at higher temperature. The same held when only clusters with more than four well developed flowers were considered. Red light during the night significantly increased flowering on the main shoot, at least when cluster quality was not taken into account. In both cultivars cluster quality was poor in all treatments.