Finally, proof that leaf floral induction with photoperiodic dependent flowering does not occur in the grapevine plant (Vitis vinifera L. 'Chardonnay')

Abstract

This research study, for the first time, presents unequivocal evidence that leaf derived photoperiodic dependent flowering (PDF) does not occur in the grapevine. The morphological changes in the shoot apical meristem (SAM), at the beginning of the flowering pathway in angiosperms, are described as starting in two possible ways: with floral induction stimulus from the leaf or a non-leaf stimulus directly on the SAM. Floral induction, floral evocation, floral initiation then floral development are defined and discussed, together with the current concepts and classification of plant PDF. The only two research papers in the English language literature suggesting grapevine PDF absence are described, with a detailed analysis in the discussion that raises doubt as to the validity of the data and subsequent conclusions. To examine the hypothesis that "leaf derived PDF does not occur in the grapevine" Vitis vinifera L. 'Chardonnay' grapevines were completely defoliated from budburst as leaves appeared, and compared to a control group (where all leaves were left) by microscopic dissection of compound latent buds at 31, 54 and 76 days post budburst. Latent bud inflorescence primordia developmental stages, at each of the sample dates, were the same in treatment and control groups. The experimental data supports the hypothesis, indicating that leaves, with floral induction, are not needed to initiate the grapevine flowering pathway. The initial stimulus to commence grapevine flowering is directly on the compound latent bud vegetative SAM with no leaf involvement. Further research investigating the presence or absence of floral evocation in grapevines, and its timing if the event occurs, is now enabled.