Does gibberellin treatment inducing parthenocarpy affect development of fruits from fertilization in pear (Pyrus communis ‘Conférence’) ?

Pear (Pyrus communis) is the main fruit crop in Belgium and ‘Conférence’ accounts for 90% of the pear production. ‘Conférence’ is self-incompatible and thus requires cross-pollination to produce fruits by fertilization. Hives could be settled in the orchards to facilitate pollination and to allow a better fruit size production. However, blooming occurs early in the spring and climatically unfavorable conditions (frost, low temperatures, rain, etc.) could prevent the pollination by insects. To overcome this inconvenience, parthenocarpy induction by spraying gibberellins is a common practice in ‘Conférence’ orchards. However, whether gibberellin treatment affects fruit set and quality of fruits produced by fertilization has not been investigated. We therefore compared the impact of gibberellin spraying on the development of parthenocarpic fruits and fruits obtained by fertilization. Un-pollinated, open-pollinated and hand-pollinated flowers were sprayed or not with 10 mg L^-1 GA4/7 at the balloon, full bloom and petal fall stages and the resulting fruit production and quality were assessed. Compatible hand-pollination increased fruit size and fruit weight by respectively 9 and 8% and decreased fruit length by 10% compared to parthenocarpic fruits whatever the gibberellin treatment. Treatment with GA4/7 increased the fruit set at harvest compared to untreated fruits. The time of GA4/7 spraying significantly affected fruit parameters and treatment was more efficient when applied at the balloon stage. Regarding fruits produced by fertilization, GA4/7 treatment decreased seed development by respectively 12, 13 and 36% when applied at the balloon, full bloom and petal fall stages compared to untreated fruits. Consequently, fruit size decreased by 2 and 5% and fruit weight by 8 and 13% when GA4/7 was sprayed at full bloom and petal fall stages compared to untreated fruits. However, treatment at the balloon stage did not affect fruit size and weight. Thus, our results showed that GA4/7 treatment negatively affect the development of fruits from fertilized flowers, depending on the timing of spraying.