Issue link: http://winesandvines.uberflip.com/i/63937
GRAPE GRO WING Rootstocks Deal With Drought Research reveals best choices for various vineyard conditions By Paul Franson n more than a century of fighting phylloxera, winegrowers have tended to select grapevine rootstocks that resist the destructive pest. With progress, other considerations have come to light: Viruses, nematodes, limited vine life spans, crop productivity and soil issues have become major con- cerns. Most recently, water usage and conservation have emerged as vitally important issues. In many areas where grapes grow well, it's only because they've been irrigated—and in some cases are protected from drought by spraying. This is true in most of California, Washing- ton and many other areas. But future restrictions on water for environmental reasons and because of increasing demand seem likely to make drought-resistant vines and rootstocks key, along with tolerance for salt and other minerals. However, balancing all the requirements including drought tolerance can be tricky. Dr. Andy Walker from the Viticulture & Enology department at the University of California, Davis, recently discussed rootstocks for dry climates and saline soils, starting with a history of rootstocks. I back to basics Rootstocks were developed by French researchers to address grape phylloxera in the late 1800s. French scientists came to the SpecTrellising_July10.qxp 5/13/10 9:25 AM Page 1 Highlights • The search for phylloxera-resistant rootstock continues. Vitis riparia and V. rupestris root well from dormant cuttings. • Andrew McElrone and Andy Walker are breeding rootstocks to tolerate drought and control growth. • They have been sourcing wild grapevines in the Southwest; thus far the samples are very diverse. United States to collect species resistant to phylloxera, a native American bug that devastated much of Europe's grapevines when American grapes were exported to Europe in hopes of develop- ing hardier vines. The scientists collected many cuttings, but only Vitis riparia and V. rupestris rooted well from dormant cuttings. These re- main important components of today's rootstocks. Vitis riparia is native to North America from the Rocky Moun- tains to the Atlantic Ocean, and from Canada to Texas. It natu- rally grows in alluvial soils in riparian habitats, and it climbs in trees and shrubs. It has shallow roots and low vigor but matures rapidly. It resists phylloxera and is easy to propagate, but it is susceptible to lime in the soil. One example is Riparia Gloire. Vitis rupestris grows from Texas to Tennessee, but it is rela- tively rare now: Much of its habitat has been destroyed. It's a shrubby plant found in rocky creek beds, and it rarely climbs. The deep roots of Vitis rupestris induce vigor, but they are not very drought tolerant on shallow soils. It resists phylloxera and is easy to propagate, but it has variable nematode resistance or lime tolerance. One example is St. George rootstock, which is virus tolerant but susceptible to nematodes. In early tests, vineyards grafted onto these species grew well ini- tially but began to decline on limestone-based soils. Un-grafted vines of these species thrive on lime-based soils, but scions grafted on them do not take up enough iron, so the French scientists returned to the U.S. and, with the assistance of T.V. Munson, collected Vitis species from the limestone plateau of central Texas. Vitis berlandieri grew in limestone soils in Texas. It is consid- ered a subspecies of V. cinerea, var. helleri, and climbs on trees. It is found in deeper soils between ridges and is deep rooted with some drought tolerance, variable phylloxera resistance and good lime tolerance. It is difficult to propagate. The scientists also experimented with a few other species for breeding rootstocks including V. longii (V. acerifolia), V. champinii and V. cordifolia. None propagate as easily as the V. riparia- and V. rupestris-based rootstocks, but V. berlandieri was the best of these, 72 Wines & Vines MAY 2012