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64 WINES&VINES March 2018 GRAPEGROWING WINE EAST LANCE CADLE-DAVIDSON I magine you are a wheat breeder. Your overarching goal is to produce varieties that increase yield by incorporating su- perior genetic traits such as large heads with more seeds, short stems and dis- ease resistance. You can make crosses of numerous elite parents that generate thousands of seedlings each year. Because each cross produces a family of hundreds of siblings, you can map the inheritance of yield components. It's an annual crop, so you see results of your efforts within months. By taking the seeds to the Southern Hemisphere, you can cycle through two or more generations per year. Measuring yield is relatively simple—and cheap. This process has been remarkably success- ful. Winter wheat yields have increased by 0.4 bushels (bu) per acre each year since 1960, and wheat farmers now produce 45 bu/acre, up 80% from 25 bu/acre in 1960. To cite another example, corn yields have increased fivefold since 1930. Now imagine you are breeding wine grapes. Your goal is a new variety that com- bines powdery mildew resistance with excel- lent fruit quality and yield. You start by emasculating flowers (using tweezers to painstakingly remove pollen-producing sta- mens) and bagging each cluster to prevent stray pollen from fertilizing them. You then take pollen you have collected from a male parent and spread it over the emasculated flowers of the female parent. Each cluster might produce 50 to 150 seeds. You plant those seeds the next year and observe seedling plants, then discard those that are susceptible or have growth defects. You select the best 5% to 15% of seedlings and replant them to a vineyard. In another three or four years, you can finally evaluate fruit characteristics and discard another 90% of the vines. Soon you can sample wines made from the most promising single vine selections, and then throw out another 90%. Measuring yield and most other traits is costly, and a single year's data is insuffi- cient—three- to five-year averages are needed for this perennial crop. Other quality metrics (e.g., fruit chemistry) are important, as are sensory attributes of wines made from the fruit. Odds are you will need more gen- erations to find a vine that combines all your desired traits. The bottom line is that, with grapes, it can take more than 15 years after the initial crosses to find out what you have, how it performs and to identify the most promising vines, which likely will be parents for the next generation. Crossing, selecting and evaluating new grapevines takes a lot more time and expense than evaluating a new hy- brid strain of wheat or corn. The numbers game and mapping Progress in breeding is determined by num- bers and time. Aside from the built-in time lag involved in growing grapes, the less obvi- ous consequence is that each grapevine takes up more space and costs more to grow and evaluate than wheat or corn. Grapevines are planted at densities of less than 1,000 plants per acre, as opposed to wheat and corn at upwards of 100,000 per acre. And they re- Grape Breeders No Longer Flying Blind Low cost of DNA sequencing allows breeders to incorporate disease resistance By Tim Martinson Many genes associated with powdery mildew resistance have been identified, including the REN4 gene expressed in the seedling above.