Tolerance to Lime - Induced Chlorosis and Drought in Grapevine Rootstocks - Abiotic Stress: Plant Responses and Applications in Agriculture - page 292

to recommend them for planting in individual sites/localities with regard to their availability
of water.
Some studies dealt with the Wue of individual botanic species and rootstocks. A higher Wue
value was found out in Vitis rupestris while a lower one in Vitis doaniana, Vitis californica and
Vitis candicans (Padgett-Johnson, et al., 2003). Higher Wue values were also described in Vitis
riparia (Flexas et al., 1999) and the rootstock 110 R (Pou et al., 2008).
Soar et al . (2006) reported that rootstock effect on gas exchange of vineyard-grown grapevines
is most likely due to differences in the relative capacity of rootstocks to extract and provide
scions with water. Rootstocks have been reported to affect the efficiency of water transport to
the shoots via conductivity constrains imposed by the anatomy of xylem vessels (De Herralde
et al ., 2006).
Greenspan (2006) differentiates between terms “drought-tolerance” and “drought-avoid‐
ance”. Drought-tolerance refers to the ability of the rootstock to support grapevine physio‐
logical functions during periods of low soil moisture availability. Rootstocks may exhibit
drought-tolerance through several mechanisms:
Maintaining a low hydraulic resistance to water flow, even under dry conditions.
1. Maintaining photosynthetic activity in leaves, even under low water availability condi‐
tions.
2. Preventing the abscission of leaves during periods of low water availability.
Drought-avoidance refers to the ability of the rootstock to prevent low vine water status by
one or more of many mechanisms, including:
1. Deep or extensive root exploration to fully exploit soil moisture reserves.
2. Conservation of vine water use by inducing closure of the leaf stomatal pores to limit
transpiration.
3. Restricting vine vigour, thereby limiting the amount of transpiring leaf surface area.
The relationship existing between the response of plants and the drought-induced stress
influences, through physiological reactions of plants, also the development of important
qualitative parameters of grapes (Lovisolo et al., 2010):
1. Effects of plant metabolism, above all photosynthesis and transpiration, on accumulation
of sugars and secondary metabolites in berries.
2. Consequences at the berry level of both the chemically-mediated long distance signalling
between root and shoot (essentially cytokinin and ABA) and the whole-plant hydraulic
control via both the xylem and the phloem from root to berry.
3. Adaptation of berry metabolism to a severe osmotic stress existing in berry cells.
ABA, which is present in xylem fluid represents a key signal of root-shoot in plants that are
stressed by drought (Schachtmann & Gooder, 2008).