Development of parthenocarpic fruits in the pear (Pyrus communis) cultivar Conference

Pear is the second fruit production in Belgium and the cultivar Conference represents 90% of this production. Pyrus communis is a self-incompatible species and requires inter-cultivar cross-pollination to develop fruits. However, blooming occurs early in the Spring and climatically unfavorable spring conditions (frost, low temperatures, rain,…) could prevent the pollination by insects. In this case, parthenocarpy induction by spraying plant hormones, mainly gibberellins, is a common practice in orchards and allows achieving sufficient yield. No precise study has been carried out to determine the most efficient hormones, the best application time and the required amounts to apply. Our work aims at highlighting pear tree reproduction and focuses on parthenocarpy processes in the Conference cultivar. We investigated if intrinsic parthenocarpy due to endogenous hormones occured in Conference. We also compared the efficiency of gibberellins, auxins and cytokinins in the parthenocarpic fruit induction. Parthenocarpic fruit development was compared to fertilized fruits resulting from hand compatible cross-pollination. Spontaneous intrinsic parthenocarpy occurred in Conference, but pollen deposit (even incompatible) increased the number of fruits initiated. Gibberellins (GA3) increased the fruit set compared to the other hormonal treatments and trees treated with gibberellins and/or cytokinins produced larger fruits. Parthenocarpic fruits remained, nevertheless, smaller than fertilized ones. Gibberellin inhibitor treatments showed that endogenous gibberellins do not act alone to induce parthenocarpy and polyamines quantification revealed a role for putrescine and spermine in parthenocarpy induction in Conference.