Reassessment of seed influence on return bloom and fruit growth in 'Bartlett' pear

In a simple, yet elegant experiment conducted 30 years ago, Chan and Cain ( 1967) using 'Spencer Seedless', a facultatively parthenocarpic apple (Malus x domestica Borkh.) cultivar, proposed that seeds inhibited flowering and accentuated biennial bearing in apple. Their conclusions have been extrapol ated widely to include apple and other species. We have tested the universa lity of their conclusions using 'Bartlett' pear (Pyrus communis L.), a comm ercially important, facultatively parthenocarpic cultivar. Unlike 'Spencer Seedless' apples and seedless 'Bartlett' pear grown in France, California-g rown seedless 'Bartlett' pear fruit strongly inhibited flowering the follow ing year. However, the presence of seeds increased 'Bartlett' pear fruit si ze relative to seedless fruit by 13% and 20% in nonthinned and heavily-thin ned pear trees, respectively, indicating that seeds increased fruit sink st rength.