The effect of soil temperature on lateral shoot formation and flower-bud formation in apple in the first year after budding

Under controlled environment conditions the influence of four soil temperatures (7°, 14°, 21°, and 28°C) on vegetative development and flower-bud formation of apple trees (cvs ‘Rode Boskoop’ and ‘Elstar’) were evaluated in the first year after budding. Relative air humidity was high, air temperature was 20°C. Broadly speaking, for both cultivars shoot growth clearly increased with increasing soil temperature. The effects on growth were mainly reflected in the number (not length) of the lateral shoots; the growth of the main shoot was little influenced by soil temperature. At 7°C the lateral shoots usually occurred higher along the main stem than at the higher temperatures. Flowering on the parent stem and on the lateral shoots was little affected by the soil temperatures tested. In general, flower-cluster quality was rather poor. If only clusters having more than four well-developed flowers are considered, flowering was favoured by higher soil temperatures; at 28°C, especially, cluster quality was much better than at the other soil temperatures. It is concluded that soil temperature is important in controlling the degree of lateral shoot-formation as well as the formation of well-developed flower clusters.