Morpho-Anatomical Observations during Bud Break in Vitis vinifera L.

The widespread distribution of grapevine is due to their large genetic variability, as well as the relative low chilling requirement of buds to overcome winter dormancy (50-400 h at <7 degrees C). Irregular bud break, reported when grapevine does not satisfy its chilling requirement, can cause poor uniformity of fruit development, while it has been shown that grapevine budbreak usually improves with increased exposure to chilling temperatures. The Baggiolini phenological stages (1952) were proposed for grapevine, characterised by simple descriptions of stages between budburst and fruit set. Afterwards a more specific evaluation method was realised by Eichhorn and Lorenz (1977) which proposed the BBCH system with transitional stages. Among the dormant and 'woolly' bud, occur important small changes corresponding to some sub-phases, that are not correctly studied and that could be an early signal of dormancy bud breaking. The 'greentip' stage (07) is generally considered indicative of 'budbreak', but it is difficult to identify precisely, because its duration is very short. The aim of this study is to explore the first phases of bud sprouting from a morphological point of view, to better define the phenological bud changes and to find the sub-phase as a clear indicator of budbreak under the climatic conditions of the Tuscan coastal area (Pisa, Italy-lat. 43,02N, long. 10,36E). Plant material of two diffused cultivars of Vitis vinifera: 'Cabernet Sauvignon' and 'Sangiovese' were utilised. After accumulation of 1250 Chilling Units (CU) dormancy breaking on two-node cuttings, by forcing method was evaluated (18 days at 25 degrees C, 60-70% relative humidity, 12/12-h photoperiod). Bud opening evolution was marked by the phenological stages (BBCH scale) reached in two day intervals under forcing and field conditions. Morpho-anatomical evolution of bud tissue was studied on fresh material under stereomicroscope. Heat requirement (GDH) was also calculated. The first stages of bud evolution were distinguished in both genotypes which showed a different GDH requirement. In relation to the morphological characteristics, stage 03 (bud scales opening) is suggested as a suitable early indicator of bud break in Vitis vinifera.