Environment and position of first bud to break on apple shoots affects lateral outgrowth

A study was conducted to determine which bud (terminal or lateral) breaks first, and thereby exerts primigenic dominance, on ‘Granny Smith’ and ‘Golden Delicious’, 1-year-old apple (Malus × domestica Borkh.) shoots grown in two locations in the Western Cape, South Africa, with differing degrees of chilling. Primigenic dominance of laterals was more common in a warm area than a cool area, and more common in ‘Granny Smith’ than ‘Golden Delicious’. Laterals rarely broke before the terminal in ‘Golden Delicious’, and so differences in lateral development due to position of first bud to break were only analyzed in ‘Granny Smith’ shoots from this point on in the study. In ‘Granny Smith’, lateral budbreak and growth was influenced by the position of the first bud to break on the shoot, but did not differ between locations. On ‘Granny Smith’ shoots with primigenic dominance of the terminal, lateral budbreak and growth was suppressed, in accordance with the typical ‘delayed foliation’ commonly observed in warm winter climates. However, when at least one lateral broke before the terminal, lateral budbreak and growth were similar to previous observations in cold winter areas.