Setting up molecular markers of flower induction in two Super High Density Olive tree varieties with divergent vegetative vigour

Biennial bearing and alternate flowering in olive trees represent a significant problem for the olive oil market. This phenomenon, involves high-yielding years followed by low-yielding years, causing economic instability for producers and difficulties in production planning. To address these challenges, the adoption of super-intensive olive groves and of varieties less prone to alternate bearing, are promising strategies. The super-high-density (SHD) olive groves allow for more efficient management of resources and more constant production over time. Two varieties (Lecciana and Coriana), recently developed for SHD groves, selected for their early flowering habit, were studied for the set-up of predictive molecular markers for flower induction. Leaf and bud samples were collected in two distinct periods before (October) and after (March) flower induction from one-year shoots of the two varieties. RNA was extracted and subsequent gene expression was analysed by quantitative PCR (qPCR). To monitor the induction of flowering in the selected varieties, the expression of the main olive FT (FLOWERING LOCUS T) and encoding genes OeFT1 and OeFT2, known for their role in the transition from the vegetative to reproductive phase in plants, was studied in leaves and lateral buds. The results showed that the presence and expression of OeFT genes are directly associated with flower induction after winter colds, as expected in olive, suggesting a crucial role of this gene in regulating the reproductive cycle of olive trees. At the same time, biometric analyses were carried out on both varieties to determine their vigour and its relationship with flower induction, by systematically evaluating the growth dynamics of the shoots in terms of shoot length, number of nodes and length of internodes.