Fruit at First Leaf

Grapevines undergoing Precise Indoor Vine Conditioning

By Kyle Freedman, Amanda Lewis, Cristian Collado, Ricardo Hernández and Mark Hoffmann

Researchers at North Carolina State University are working on changing a fundamental aspect of grape growing: that new vines require at least two years to produce usable fruit. Their project, called Precise Indoor Vine Conditioning (PIVC), conducted in collaboration with lighting partner Current, could yield grapevines that can be planted and cropped in the very same year.

Understanding cluster development is key to the research. Like many woody plant species, grapevines develop clusters over two seasons. The development of inflorescence primordia (the early developmental stages of a group of flowers) happens in the first year within the dormant buds. Budbreak and the development of clusters happens in the second year, bearing the vine’s first fruit later that season.

The dilemma is that a mature grapevine must develop inflorescence primordia for next season, while developing fruit for this season. Optimal conditions for primordia development are not necessarily the same as for fruit development. High temperatures, moderate to low nitrogen and high light intensities are important to develop inflorescence primordia, yet the same factors can hinder the development of high-quality fruit. For young vines, grape growers typically opt to develop the primordia, delaying production till at least the third leaf.

The NCSU team, led by second-year Ph.D. student Kyle Freedman, hopes that PIVC can help growers balance the development of next year’s crop with the floral development of this year’s transplant. Lighting, they’ve found, is an important part of the project.

Working with Current in a greenhouse setting, the team identified the optimal lighting conditions under which a vine develops the greatest amount of inflorescence primordia and eventually clusters. Using Current’s advanced, programmable LED lighting options, they investigated the impact of different—and very precise—light intensities (amount of light) and durations of exposure (photoperiod) on primordia and cluster development, hence, the project name.

Kyle explained that the purpose of a controlled environment with advanced lighting is to give the grapevines ideal conditions to promote growth and development. During traditional nursery production, young grapevines experience a wide range of environmental conditions, such as reduced light from shading and cloudy days, and temperature fluctuations, both of which can inhibit growth and development. “While we don’t anticipate a shift from vineyard-grown grapes to greenhouses,” Kyle noted, “we do believe this system could provide new methods of nursery production and supply growers with stronger plants that could yield harvestable fruit earlier.”

Results from the light conditioning phase of Kyle’s research show that net photosynthetic rate increases significantly for Traminette moving from low to high supplemental light intensity and from low to medium for Concord. This distinction is important as not all plants can process additional amounts of light for photosynthesis, which is essential for increasing fruiting capacity. In addition, clusters were counted on the indoor-conditioned Traminette vines after they were transplanted in a local North Carolina vineyard, with the highest cluster counts observed in vines that had received medium supplemental light intensity in the greenhouse. With optimal light intensity to increase fruitfulness thus identified, it can be tested on future cultivars. Next steps in Kyle’s research include investigating the impacts of container size on root development as well as evaluating whole system’s economic feasibility.

This article was adapted from the original, titled Annual Grape Production: Only a Photon Away, published on the Current website on February 9, 2023.