Difference between pollination and parthenocarpy in the 'Conference' pear production

Pear (Pyrus communis) is the first fruit crop in Belgium and ‘Conference’ represents 90% of the pear production. As a self-incompatible species, pear tree requires cross-pollination to develop fertilized fruits. Hives could be settled in the orchards to facilitate pollination and allow a better fruit size production. However, blooming occurs early in the spring in Belgium and unfavorable weather conditions (frost, low temperatures, rain, etc.) could prevent the pollination by insects. In this case, parthenocarpy induction by spraying phytohormones, mainly gibberellins, is a common practice in ‘Conference’ orchards. Our work aims to better highlight the pear tree reproduction and focuses on the pollination and parthenocarpy processes in ‘Conference’. Field trials were realized during 3 years to compare fruits resulting from 1) spontaneous intrinsic parthenocarpy with emasculated flowers, 2) induced intrinsic parthenocarpy with flowers pollinated with intra-cultivar incompatible pollen, 3) induced extrinsic parthenocarpy with phytohormones (gibberellins, cytokinins or auxins), 4) hand compatible inter-cultivar pollination, 5) open pollination by insects. We observed that spontaneous intrinsic parthenocarpy due to endogenous phytohormones occurred in ‘Conference’. However, pollen deposit (even if incompatible) increased the number of fruits initiated by 10 to 40% depending on the climatic conditions. Gibberellin treatments could also increase the parthenocarpic fruit set under adverse weather conditions. However, phytohormone treatments did not particularly increase fruit weight and fruit size in relation to extrinsic parthenocarpy. According to the year, parthenocarpic fruits remained, nevertheless, up to 12% smaller than fertilized ones. Our results also suggest that endogenous gibberellins do not act alone to induce parthenocarpy since gibberellin inhibitor (paclobutrazol) treatment did not completely prevent parthenocarpic fruit initiation.