Most of the grapes in Washington State are grown on their own roots (non-grafted) due to the limited presence of phylloxera. This aphid-like insect forms galls on roots and occasionally leaves, and can cause premature shoot defoliation, vine decline, and eventual death. Since there are no chemicals to treat phylloxera, most growers simply graft wine grape varieties onto phylloxera-resistant rootstocks.
Recently, chip bud grafting in Washington State vineyards has been used to change existing varieties to a new variety to increase economic gain, depending upon market conditions and consumer needs.
Grafting combines two separate plant pieces, a scion and a rootstock (Figure1). The scion wood is the variety desired for fruit production, while the rootstock portion of the vine serves as its root system.
During the grafting process, callus is formed, which are undifferentiated cells that bind the scion and rootstock together. These cells differentiate into specialized cells that form a new xylem (water and nutrient pathway) and phloem (sugar pathway) within the graft union. Several different grafting techniques can be used to produce complete grapevines or top-work varieties in the field. Bench grafting of rootstocks and scions is often used in a nursery setting (Table 1). These vines are then callused in the nursery to develop the graft union before field planting. Field grafting is used on vines designated for top-working (Table 1), and requires protection with waterproof paraffin, paint, or grafting tape. The graft union then calluses and differentiates into xylem and phloem in the field.