This first installment of a two-part report includes some abstracts of recent articles that deal with the part of the grapevine we don’t see—the rootsystem and its immediate environment. This installment includes articles related primarily to rootstock’s effects on vine performance: yield, berry composition, scion physiology, etc. The second group of abstracts deals with pest problems that may be reduced by rootstock choice such as viruses and nematodes.

(Editor’s note: Important research in Washington state on rootstock use versus own-rooted vines did not fit into this report but will be covered separately in a coming issue of Wines & Vines.)

Rootstock and Shiraz
Shiraz grapevines either own-rooted or grafted to three different rootstocks [Ramsey (Vitis champinii), Schwarzmann (V. riparia x V. rupestris) and 115 140 Ruggeri (V. berlandieri x V. rupestris)] at two sites in Australia (Adelaide and Nuriootpa) were used to evaluate the effect of rootstock on primary bud necrosis (PBN), fruitfulness and carbohydrate storage. Buds were dissected during winter dormancy and assessed for the number of inflorescence primordia (IP) and incidence of PBN. Trunks, canes and roots were sampled at dormancy for carbohydrate concentration. A water-deficit treatment was also applied at one of the two locations. Fruitfulness and yield were affected by water deficit. Rootstock type influenced the incidence of PBN, fruitfulness and carbohydrate concentration at both sites. 

C.M. Cox, A.C. Favero, P.R. Dry, M.G. McCarthy, and C. Collins, Amer. J. Enol. Vitic., published ahead of print March 20, 2012, doi: 10.5344/ajev.2012.11012. Contact the senior author: School of Agriculture, Food and Wine, University of Adelaide, Waite Research Institute, PMB 1, Glen Osmond, SA 5064.

Vegetative growth of Cabernet
Cover crops, rootstocks and root restriction were evaluated in Virginia to regulate vegetative growth of Cabernet Sauvignon grapevines. This was a complicated, three-factor experiment involving two cover crops [row-middle and under-trellis cover crop (UTCC), row-middle-only cover crop combined with 85cm weed-free strips in the vine row], three rootstocks [Riparia Gloire (Riparia), 420A and 101-14], and root restriction, whereby vines were either planted in root-restrictive (RR) fabric bags at vineyard establishment or planted without root restriction.

Root restriction and UTCC were independently effective in suppressing vegetative development as measured by rate and seasonal duration of shoot growth, lateral shoot development, trunk circumference and dormant pruning weights. Riparia was the most effective rootstock in limiting vegetative development among the three evaluated. Under-trellis cover crop reduced cane-pruning weights by 47% relative to vines grown on herbicide strips. Canopy architecture was generally improved by both UTCC and by root restriction, but generally unaffected by rootstock.

The principal direct effect of the UTCC and the root-restriction treatments was a sustained reduction in stem water potential. Results suggest practical measures can be used to create a more favorable vine balance under conditions of variable rainfall, such as exist in the eastern United States. 

T.A. Hatch, C.C. Hickey and T.K. Wolf, Amer. J. Enol. Vitic. 62:298-311 (2011). Contact the senior author: Virginia Tech, (540) 869-2560; thatch@vt.edu.

Drought-tolerant grape root system
The role of root systems in drought tolerance is a subject of very limited information compared with above-ground responses. Adjustments to the ability of roots to supply water relative to shoot transpiration demand is proposed as a major means for grapevines to tolerate drought. Seasonal root proliferation in a directed manner could increase the water supply function of roots independent of total root area and represents a mechanism whereby water supply to demand could be increased.

To address this issue, seasonal root proliferation, stomatal conductance (gs) and whole root system hydraulic conductance (kr) were investigated for a drought-tolerant rootstock (Vitis berlandieri x V. rupestris 1103P) and a non-drought-tolerant rootstock (V. riparia x V. rupestris 101-14 Mgt), upon which had been grafted the same clone of Merlot. Leaf water potentials for Merlot/1103P were +0.15 MPa higher than Merlot/101-14 Mgt during spring, but dropped by ≈ -0.4 MPa from spring to autumn and were lower by -0.15 MPa than for Merlot/101-14 Mgt. Surprisingly, gs of Merlot on drought-tolerant 1103P was less down-regulated, and canopies maintained evaporative fluxes ranging from 35-20 mmol/vine/s during the diurnal peak from spring to autumn, respectively, three times greater than those measured for Merlot on drought-sensitive 101-14 Mgt.

Drought-tolerant 1103P grew more deep roots during the warm summer dry period, and the whole root system conductance (kr) increased during that same time period. The manner in which drought tolerance was conveyed to the drought-sensitive clone appeared to arise from deep root proliferation during the hottest and driest part of the season, rather than through changes in xylem structure, xylem density or stomatal regulation. This information can be useful to growers on a site-specific basis in selecting rootstocks for grape clones that may be particularly drought-sensitive.

M.M. Alsina, D.R. Smart, T. Bauerle, F. de Herralde, C. Biel, C. Stockert, C. Negron and R.J. Save, Experimental Botany 62:99-109 (2011). Contact the senior author: Department of Viticulture and Enology, University of California, Robert Mondavi Institute North, 595 Hilgard Lane, Davis, CA 95616.