Buds of “Italia melhorada” grapevines grown under tropical conditions develop a quiescent state

Abstract A double cropping system for the grapevine (Vitis vinifera L) has been commercially adopted for use in regions where the tropical climate is characterized by high temperatures and small variations in daylength throughout the year. Under these climatic conditions, the use of hydrogen cyanamide (HC), a compound that breaks bud dormancy, is mandatory to produce homogeneous budbreak. However, it is unknown whether grapevine buds are capable of developing endodormancy (ED) under these climatic conditions. In this study, typical signals of ED, such as the number of nodes per cane, the development of periderm and the thickening of the cell wall of the bud meristematic cells, were analysed in vines of “Italia melhorada” grown in Mossoro, Brazil (5o12’16”S ), under a natural (ND) photoperiod (12/12 h), a short-day (SD) photoperiod (10/14 h) and a long-day (LD) photoperiod (14/10 h). The abundance of phytochrome A (VvPHYA) and B (VvPHYB) and FLOWERING LOCUS T (VvFT) transcripts in the leaves and buds was also determined. The results showed a reduced number of nodes per cane and development of the periderm in the shoots of grapevines grown under ND and SD photoperiods. In addition, compared with that under the LD photoperiod, the expression of VvPHYA and VvFT under the ND and SD-photoperiod decreased, and the expression of VvPHYB increased. However, the thickness of the cell wall of the bud meristematic cells increased only in the grapevines exposed to the SD photoperiod. Therefore, we hypothesize that cell wall thickening is a characteristic of ED, while decreased expression of VvPHYA and VvFT and increased expression of VvPHYB are characteristic of quiescence. Consequently, under a tropical conditions, the grapevine buds would be in a quiescent state and not in a dormant state.