In the Vineyard If spraying is unavoidable...


The best course of action is a carefully calculated programcombinedwith induction of phytoalexin response.


By Gary Strachan


he Holy Grail of viticulture is to achieve spray elimination. This is not simply attainment of organic status or the use of sustainable practices, it’s the seemingly impossible task of staying out of the vineyard with a tractor and sprayer.


T GARY STRACHAN


A few months ago I reviewed Lon Rombrough’s book on organic viticulture. One point that I remember was attributed T.V. Munson, the noted grape breeder from Texas. During the selection of wild grapes for breeding, he paid attention to the environment in which the grape was growing. For example, not all native Vitis rupestris or Vitis rotundifolia is the same. The survivors in a particular ecological niche are only there because they have become resistant to all of the pathogens and environmental stresses of that niche. Even if you introduce other grapes of the same species into that area, there is no guarantee of their immediate adaptation to their new environment.


The western coast of North America has no native grape species. Everything we grow has been introduced from somewhere else. So have most of the pests. Our semi-arid climate was a barrier to grape species and their pathogens, but by introducing viticulture we also created a favourable climate for pathogens. Is it even possible to cultivate grapes without their pathogens appearing?


Grapes are remarkably resilient.Even without human intervention, Vitis vinifera, the best-known wine grape, was colonized in western Europe from the species origin, mostly in the eastern Mediterranean. The eastern half of North America was colonized by many localized species that were resistant to native diseases, but the failed introduction of European vinifera by early colonists is a well known story. We now know that the native species


Sovereign Coronation, a seedless table grape bred in Summerland. These were grown this year with no sprays. Also resistant to bird damage.


possessed disease-resistant genetic qualities that were not expressed in European grapes.


All grape species have defences against abiotic stresses such as heat, drought, salinity and ultraviolet radiation, but some species and cultivars have much greater resistance than others.


All species exhibit the ability to induce phytoalexins in response to abiotic or biotic (infectious agent) challenge. Phytoalexin is a general term applied to substances produced by a plant to ward off a disease state. A good depiction of this is the familiar table that lists susceptibility of commercial grape cultivars to mildew infection. Some hybrid varieties that contain Vitis labrusca genes may be almost immune to powdery mildew whereas other vinifera varieties such as Bacchus or Chardonnay are quite susceptible. This begs the question of how can we induce resistance into mildew susceptible varieties?


In our age of genetic manipulation, an obvious strategy would be to simply transfer the genes responsible for mildew resistance. This has already been done, not only in grapes but also in wheat. The stilbene genes of grapes can confer resistance to fungus infection in wheat.


In spite of our ability to create disease-resistant grapes, it won’t likely happen until the public becomes more accepting of GMO foods. Most people


avoid GMO foods if they have a choice.


Conventional breeding


and selection such as the projects conducted in Summerland from the mid-1960s to mid-1980s have selected grapes with greater resistance but seldom have resulted in widespread adoption of new varieties, with the exception perhaps of Sovereign Coronation, a productive, easily grown, seedless table grape. New wine grape


selections with unfamiliar flavours and names are unable to displace the handful of familiar European varieties that have set the standard for


wine character and quality for hundreds of years.


Despite 50 years of growing productive, hardy, partially mildew- resistant hybrids in B.C., when our wine industry was shocked by NAFTA, the redeveloped industry was based on a few familiar vinifera varieties that we had also evaluated during the early 1980s while we were testing the hybrid selections from Summerland and other breeding projects.


For now, the best course of action is to maintain a carefully calculated spray program combined with a planned induction of phytoalexin response. For example, regulated deficit irrigation (RDI) induces the plant’s drought response strategy. Early season cluster exposure induces the plant to defend against ultraviolet radiation. Mycorrhizal inoculation at planting and during mulching induces plant defences against fungal infection. A bonus to winemaking is that the phytoalexin response produces increased tannin, flavonoid, anthocyanins, terpenes and resveratrol. These are are compounds that inhibit fungi and are associated with higher quality wine.


Eventually we will select new grape varieties in which these compounds are part of the plant’s constitutive metabolism, but for now we must remain aware of how we can work with the plants to keep them healthy. The best wines are produced in a healthy vineyard.


British Columbia FRUIT GROWER • Fall-Winter 2017 23


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