Abstract
In modern viticulture, grafting commercial grapevine varieties on interspecific rootstocks is a common practice required for conferring resistance to many biotic and abiotic stresses. Nevertheless, the use of rootstocks to gain these essential traits is also known to impact grape berry development and quality, although the underlying mechanisms are still poorly understood. In grape berries, the onset of ripening (véraison) is regulated by a complex network of mobile signals including hormones such as auxins, ethylene, abscisic acid, and brassinosteroids. Recently, a new rootstock, designated M4, was selected based on its enhanced tolerance to water stress and medium vigor. This study investigates the effect of M4 on Cabernet Sauvignon (CS) berry development in comparison to the commercial 1103P rootstock. Physical and biochemical parameters showed that the ripening rate of CS berries is faster when grafted onto M4. A multifactorial analysis performed on mRNA-Seq data obtained from skin and pulp of berries grown in both graft combinations revealed that genes controlling auxin action (ARF and Aux/IAA) represent one of main categories affected by the rootstock genotype. Considering that the level of auxin tightly regulates the transcription of these genes, we investigated the behavior of the main gene families involved in auxin biosynthesis and conjugation. Molecular and biochemical analyses confirmed a link between the rate of berry development and the modulation of auxin metabolism. Moreover, the data indicate that this phenomenon appears to be particularly pronounced in skin tissue in comparison to the flesh.
Highlights
In Europe, Vitis vinifera varieties are grown as scion grafted onto a rootstock
Based on Color Index for red Grapes (CIRG) index values, the pigmentation of berry skin in Cabernet Sauvignon (CS)/1103P displayed a 14-days delay compared to CS/M4, while at harvest (E-L38) berries from both graft combinations reached the same CIRG value, confirming a recovery from CS/1103P (Figure 1C, Supplementary Figure S1)
The different evolution of berry development and ripening in CS/1103P and CS/M4 berries was observed in 2012 (Supplementary Figure S2), the two growing seasons were characterized by significant differences in temperature excursions as described in Supplementary Data S1
Summary
In Europe, Vitis vinifera varieties are grown as scion grafted onto a rootstock. At first, grafting was adopted with the aim of preventing devastation to European viticulture by Phylloxera. This gradually imposed the use of rootstocks as general practice and the development of new rootstock genotypes became an important issue in modern viticulture (Whiting, 2004). Rootstocks can be used to confer other advantages affecting physiological processes at the scion level, such as biomass accumulation, quality yields, vine vigor, and grape berry quality (Walker et al, 2000; Gregory et al, 2013; Berdeja et al, 2015). The beneficial effects of rootstocks on stress resistance and vegetative growth represent an extremely important issue in viticulture, but their effect on grape development rates and on berry quality warrants investigation. It is widely known that the rootstock influences grapevine reproductive performance and berry development (Kidman et al, 2013), studies addressing the relationship between a given graft combination and the berry ripening evolution are still lacking
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