Factors influencing reproductive development and dry mass allocation in pears

For consistent yields in pear fruit production, knowledge of the development of the reproductive bud is required.  Detail on the development of the bourse shoot primordium within the reproductive bud was followed and correlated to the bourse shoot growth of the different cultivars.  The effect of scoring on reproductive bud induction was evaluated and the effect of pruning on dry mass allocation monitored in ‘Packham’s Triumph’ during 2002/04. The sink strength of primary growth increased by 40 % for short bearing units (SBU’s) and 140 % for thick bearing units (BU’s) as compared to long bearing units (LBU’s) and thin BU’s respectively.  The increase in primary growth was due to better fruit set and larger fruit in the SBU’s and the thick BU’s.  Since the increase in primary growth is less for SBU’s compared to thick BU’s the conclusion, which can be made, is that branch diameter influenced sink strength more than branch length.  In 2004/05 two cultivars were used, viz. ‘Packhams’ Triumph’ and ‘Early Bon Chretien’.  The response in ‘Packhams’ Triumph’ was similar to that found in the previous season, but no differences were found in ‘Early Bon Chretien’.  The physiological basis for the beneficial effect of scoring on flower induction was evaluated by analysing endogenous plant hormones levels following the scoring treatment in apples.  It appears however that a change in cytokinin levels 24 hours after the scoring treatment could be involved in the flower induction.