Regrowth and flowering in sweet orange after pruning

Abstract

Sweet orange trees, cv. Late Valencia, 6 m in height were moderately pruned in the spring of 1969, up to 8 % of the canopy being removed. Over 2 years, three or four growth cycles were completed. The amount of regrowth was correlated with the size of the first growth cycle flush after pruning, and this was correlated with the diameter of the pruned branch. No flowers were found on regrowths 1 year after pruning; only 75% of regrowths produced flowers 2 years after pruning, and only 50 % produced fruit. Small plants (rooted cuttings) were used to investigate pruning responses in the phytotron. Low temperatures (18/13�C) immediately after pruning for 8 weeks resulted in smaller first growth cycle flushes after pruning, and even after transfer to warm (27/22�) conditions the original height was not regained after three growth cycles. Plants that received cool conditions after the first or second growth cycles regained their original height after the third growth cycle. The amount of regrowth was correlated with the length of the first growth cycle flushes, which was correlated with the original height of the plants and the height after pruning. Flowers could not be induced on the old wood after pruning or on the first growth cycle flushes, and only few flowers were formed in the second growth cycle flushes. Many inflorescences were produced on third growth cycle flushes following inductive conditions (18/13�C) for 8 weeks. Light pruning of less vigorous plants did not inhibit subsequent flowering. The practical implications of this work are discussed. Moderate pruning will remove part of two crops, not one, because of the inability of regrowth flushes to flower until several growth cycles have formed. The tree relatively quickly replaces the growth removed, and this depends on the vigour of the first growth cycle flushes after pruning. Pruning in autumn or winter would be expected to result in less vigorous regrowth. Our lack of knowledge on the pruning responses of orange trees is emphasized, with suggestions for future practical investigations.