Next Generation Sequencing to characterise the breaking of bud dormancy using a natural biostimulant in kiwifruit (Actinidia deliciosa)

- Buds dormancy and its biostimulant-induced breaking have been characterized.
- Biostimulant's effect on bud break/flowering depends on the moment of application.
- Several changes in gene expression occur before natural bud break in kiwifruit.
- Biostimulant responsive genes were also identified.
- Basis to improve bud break-enhancing compounds and optimize their application timing.

Dormancy occurs in many woody perennials and fruit trees, and is characterised mainly by the temporal absence of growth. This strategy has an ecological role in ensuring plant survival under non-permissive growing conditions. In kiwifruit (Actinidia deliciosa), buds must be exposed to a certain amount of chilling to complete dormancy and achieve optimal bud break and flowering in spring. However, in warmer geographical areas bud break can be limited by insufficient winter chilling, leading to less and uneven flowering and lower productivity. Several bud break-enhancing compounds have been shown to be effective in kiwifruit, overcoming the negative effects of poor winter chilling. However, their mode of action is still largely unknown. In this work, using a molecular approach based on Next Generation Sequencing, we characterised dormancy and its breaking after the application of the biostimulant Erger®. Samples were collected at different time-points and in distinct geographical areas, namely Italy and New Zealand. Our results indicated that the effect of Erger® depends on the moment of application. Furthermore, molecular mechanisms that characterise a biostimulant treatment for bud break, irrespective of the region and seasonality, were identified. This characterisation opens new perspectives to improve bud break-enhancing compound formulations and identify their best moment of application.