Molecular genetics ready to launch a golden age of winegrape breeding

The cultivation of wine grapes could be the most insular type of horticulture currently in existence. The majority of wine production worldwide is made up of just 20 cultivars of the thousands of grape varieties available. The wine industry is convinced these traditionally cultivated varieties alone provide all the diversity necessary and that newly-bred types can’t compete on wine quality. This notion persists even in the context of the latest gene research that suggests that a lot of traditional varieties of the world were deliberately crossed with older varieties. However, the landscape could change as wineries that are well-known regions adapt to the changing climate.

Through the ages, breeding

The process of clonal selection accomplishes the development of a limited variety of traditional cultivars. The people look for natural changes in bud-sports that are vine offshoots. If these changes can be beneficial (better color, size of berries, or dates of ripening), the new varieties – known as copies – are reproduced by cuttings and then distributed.

However, these naturally occurring mutations do not give the wide range of fruits and wine quality that is required to ensure excellence in the face of a changing climate. There are varieties outside of the usual 20 possibilities that could provide better fruit quality in cooler or warmer conditions, but they’ll need to be evaluated and propagated. There are new varieties that can be crossed, but they would require selection for a variety of characteristics and could take a long time. It is faster and more precise to make use of advancements in molecular genetics, which will help optimize traditional breeding methods and select for higher quality, higher climatic adjustment, as well as better disease and pest resistance.

How can you fight Pierce’s Disease?

When Europeans first arrived on the eastern coastline of North America, they brought cultivars of the European grapevine, Vitis vinifera, and Vitis vinifera, with them. The vines weren’t well-adapted to the changing environment and were quickly afflicted by insects and diseases. In the south of the US, along with Mexico, Pierce’s Disease (PD) caused the most severe impact and continues to limit the production of premium wine grapes severely. This is caused by Xylella Fastidiosa, a bacterium that reduces the xylem’s capacity to conduct water in the plant. It causes loss of water and even death of the vine. The issue of Pierce’s Disease provides a case study of the ways that molecular genetics can help solve problems that traditional breeding methods can’t.

There are a few naturally resistant to PD grapes. Grape breeders have tried to enhance their qualities for many years, but they are thwarted because several genes are responsible for every desirable trait. Disase-resistance, as well as fruit quality genes, work independently during breeding, making it hard to determine which features will end up in the descendants that these. vinifera crosses that cross-resistant varieties. In addition, the odds of finding individuals who have improved the quality of fruit while retaining resistance are extremely low.

Looking to the DNA

Recent advancements in molecular genetics have led to the development of the genetic map. They are able to track the position of desirable traits, such as resistance to disease and fruit quality, in a grape’s genetics. The easily identifiable DNA markers associated with these traits could indicate whether or not they exist. The process of selecting using tags can significantly speed up traditional breeding programs for perennial woody crops like grapes – frequently reducing generation times from 5 to 8 years to as low as two or fewer years.

Vitis Arizonica hasn’t been meticulously over the centuries, just like wine grapes. Dan Ng, CC BY-SA

My research lab has focused on PD resistance found in different varieties of V. arizonica grapes that are found in northern Mexico. This resistance is governed by a single dominant gene that we genetically identified and named PdR1. We begin by crossing V. arizonica with V. vinifera in the traditional method. The past was when we would make these crosses and needed to test the offspring for resistance, typically after a year or two after they had grown sufficient to be able to harvest cuttings to test greenhouses.

Now, we have markers for PdR1. We can grind a small amount of leaf tissue taken from the newly planted seedlings and search for DNA markers. From the beginning, we can tell what plants have resistance. In addition, it is the ability to eliminate plants that are susceptible to disease before spending time and money placing these in vineyards.

Because V. Arizonica is homozygous-dominant for PdR1, that is, there are two different functional versions of this gene; all the progenitors of the first generation in these V. arizonica / V. vinifera crosses are resistant. They contain around 50 percent V. vinifera. We intend to test the plants in order to determine which ones fight off the bacteria that cause disease most effectively and also are the most fruit-like and then make them crossbred to the V. vinifera wine variety. The progeny of that lineage are around 75 percent V. vinifera. Remember, the higher the V. vinifera is produced, the better the wine. We continue to breed new generations and back up to V. vinifera. The next generation will be 88 percent V. vinifera, then 94%, then 97 percent.

We could produce this many generations in a mere 12 years. To reduce time, we only made one or two wines during production. From our previous research, we have discovered that the odors of scents that are foxy and musty, as well as blue-purple coloration that is common to wines of American species parentage, start to fade at 88 percent V. vinifera. They are almost absent in 94 percent of V. vinifera wines. Now, we’re scouring through the thousands of 97 percent V. vinifera grapes and testing them at the greenhouse in severe, harsh conditions to determine those with the strongest resistance and the highest wine quality.

In 2015, we’ll launch a great, as-yet-unnamed percent V. vinifera wine – 07355-075 in our lab, which is made up of 50 percent Petite Sirah and 25% Cabernet Sauvignon. In one or two years, we will announce the very first 97 percent of V. Vinifera wines that have PD resistance.


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