The Effect of Scoring during Flower Induction or the Initiation Phase on Return Bloom in Pyrus communis L

The influence of scoring during the flower induction phase was investigated. Pear trees, Pyrus communis L. cv. Doyenne du Comice, Forelle and Rosemarie were used in the study, conducted in the Western Cape, South Africa. The yield of ‘Doyenne du Comice’ increased by 38% in scored trees compared to the control. The increase in yield was due to 50% more fruits on the scored trees than on the control trees. The increase in fruit number per tree was due to a higher percentage of reproductive buds per tree and the improved quality of these buds. Scoring of ‘Rosemarie’ at the correct time resulted in a 40% increase in reproductive buds. Scoring disrupts basipetal transport in the phloem, which results in the removal of apical dominance and an increase in root-derived cytokinins. More meristems can respond to inductive conditions and the higher concentration of cytokinins during inductive conditions leads to improved flower quality. INTRODUCTION A prerequisite for a large pear crop is the presence of a sufficient number of reproductive buds at the start of the season, but the quality of the flower cluster is equally important. Flower quality is measured in terms of its ability to set, retain and size fruit until harvest (Webster, 2002). To improve flower quality you need to increase the inflorescence size. Ferree et al. (2001) found a positive relationship between flower dryweight and fruit set and harvest fruit weight. There is, furthermore, a positive relationship between number of leaves and flowers in the inflorescence and fruit set (Lauri and Terouanne, 1999). Early bud development of apples is characterised by an increase in the number of appendages, i.e. bud scales, transition leaves and true leaves in the bud (Bijhouwer, 1924). Flower quality can be improved by earlier initiation, which will lead to a longer period of differentiation, or by increasing the rate of differentiation. Flower initiation is the first visible change of flower formation in the meristem, which, in pears, is seen as the broadening of the apex. Directly after flower initiation, flower differentiation follows, resulting in the formation of the different floral parts. The aim of this study was to improve the inductive conditions for initiation, thereby increasing the number of reproductive buds initiated and also enhancing the process of initiation, which will result in better bud quality. When the tree is scored at the start of flower initiation, the basipetal transport of auxin will be disrupted, which will lead to an increase in root-derived cytokinin (Li et al., 1995). This root–derived cytokinin should stimulate cell division in the developing reproductive bud, thereby raising the metabolic activity of the bud. Furthermore, the cytokinin can release meristems from apical dominance and therefore allow meristems to react to inductive conditions and become reproductive (Bangerth et al., 2000).