Does gibberellin treatment inducing parthenocarpy affect development of fertilized fruits in pear (Pyrus communis L. cv. 'Conférence') ?

Pear (Pyrus communis L.) is the most important fruit crop in Belgium and ‘Conférence’ represents 90% of the pear production. ‘Conférence’ is self-incompatible and 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 and climatically unfavorable conditions (frost, low temperatures, rain, etc) could prevent the pollination by insects. In this case, parthenocarpy induction by spraying gibberellins is a common practice in ‘Conference’ orchards. However, whether gibberellin treatment affect fruit set and quality of fertilized fruits has not been investigated. We therefore compared the impact of gibberellin spraying on the development of parthenocarpic and fertilized fruits. Un-pollinated, open-pollinated and hand-pollinated flowers were sprayed or not with 10 mg/L GA4/7 at balloon, anthesis and wilted stages and the resulting fruit production and quality were assessed. Hand-pollination increased fruit size and fruit weight by respectively 9% and 8% but decreased fruit length by 10% compared to parthenocarpic fruits whatever the gibberellin treatment. Treatment with GA4/7 increased the fruit set at harvest (28% vs. 22%) compared to untreated fruits. The time of GA4/7 spraying significantly affected fruit parameters and treatment was more efficient when applied at balloon stage. Regarding fertilized fruits, GA4/7 treatment decreased seed development by respectively 12%, 13% and 36% when applied at balloon, anthesis and wilted 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 anthesis and wilted stages compared to untreated fruits. However, treatment at balloon stage did not affect fruit size and weight. Thus, our results showed that GA4/7 treatment might negatively affect the development of pollinated fruits depending on the timing of spraying