Roma Seedless

Main Characteristics

Roma Seedless is a new table grapevine variety artificially created by American breeder Joseph Maranto in the San Joaquin Valley, California. The breeding program was initiated in 1992, and the hybrid cross was made in 1993. The female parent used was the seeded grape variety Red Globe, while the seedless variety Crimson served as the male parent. The Roma Seedless grapevine variety belongs to the late-ripening group. Under the environmental conditions of Central California, commercial fruit maturity and harvesting typically occur in late October or early November.

This variety demonstrates high productivity potential when managed with short spur pruning. The resulting yield is characterized by substantially uniform, medium-to-large clusters of a conical, shouldered shape with an average weight ranging from 600 to 1000 grams. The rose-pink berries have an average weight of 6–7 grams, featuring a very firm skin and a crisp, meaty internal texture with a sweet, harmonious flavor. At the time of commercial harvest in early November, the soluble solids accumulate to approximately 20% sugar, with an average titratable acidity level of 4.3 g/l and a juice pH of 3.7. The Roma Seedless grapevine variety possesses excellent dessert qualities and a superior shelf life during post-harvest storage.

Morphological Description of the Roma Seedless Grapevine Variety

• Vine and Cane: The mature trunk is slender and includes long split strips of bark. The bark color is brown, with a light brown underbark. The mature one-year-old dormant cane is characterized by a medium length (approximately 1.5 to 2.1 m) and a substantially circular to slightly flattened cross-section, measuring about 10 mm in diameter with longitudinal striations. The cane texture is smooth, and the shoot color is light green. The growing tip generally ascends straight up.
• Tendrils: Developed in a sparse number and arranged discontinuously along the shoot. They are smooth in texture, green in coloration, and feature a bifurcated or trifurcated substantially conical configuration.
• Buds: The buds exhibit a pointed conical shape, with an average length of approximately 6 mm and a width of approximately 5 mm. Bud break commonly occurs in the middle to the end of March. Most of the basal buds are highly fruitful.
• Leaves: The mature leaf is generally medium in size (average length of approximately 102 mm and width of approximately 106 mm) with a heavy density on the vine. The leaf blade is five-pointed, smooth, and glabrous on both the dorsal (dark green) and ventral (light green) surfaces. The petiole sinus exhibits a U-shaped configuration. The midrib color is grape green. The margins are serrate with irregular teeth, featuring approximately 12 teeth per lobe and a total of 50 to 60 teeth on the entire leaf blade.
• Flowers: The bloom date begins approximately in the middle of May, with the full bloom stage reached during the third week of May. The flowers are fertile, produced primarily at the second or third node from the base of the shoot. The corolla consists of five light green petals that open from the bottom to the top. The five sepals are poorly developed. The androecium includes six upright and diverging stamens. The yellow pollen is abundant. A single pistil produces a liquid secretion to hold pollen for germination.
• Cluster and Berry: The cluster is medium-to-large in size (average length of 17.8 to 23 cm), compact, and substantially uniform with a conical shouldered form. The berries are uniform, ellipsoidal elongated in shape, with an average longitudinal length of 27 mm and a width of 20 mm. An average cluster contains approximately 120 to 150 berries. The skin is relatively thin but very firm, displaying a red-pink/rose-pink skin coloration. Seasonal temperature variations during the ripening stage may influence the intensity of color development. The internal flesh is light pinkish, firm, and seedless.

Vine Management and Viticultural Characteristics

The Roma Seedless grapevine variety exhibits high vigor that exceeds both of its parental varieties, Red Globe and Crimson. In commercial cultivation, this grapevine variety shows high productivity with spur pruning. For asexual propagation, it has been successfully grafted onto mature Thompson Seedless rootstock. No skin cracking or tendency to split under adverse weather conditions has been encountered during observations to date. The berry capstem is strong, with long chalazas firmly attached to the vascular tissue of the fruit.

The variety shows a high level of environmental adaptability and resistance to climate stress factors. The grapevine exhibits a good ability to resist drought, wind, and extreme summer heat (with high temperatures reaching 40–42°C in the evaluation region). The level of cold hardiness is rated as good; under the conditions of Central California where winter temperatures sometimes drop to values between -1.6°C and -10.5°C (13 to 29°F), no winter injury has been encountered. The winter cold experienced is sufficient to satisfy the vine dormancy requirement. No visible disease problems or fungal infections have been encountered during observations to date. The shipping, handling, and keeping qualities are excellent; after one month in cold storage, the fruit still displays a good commercial appearance and texture. The Roma Seedless grapevine variety demonstrates an excellent keeping quality and is highly suitable for long-term storage.

* VINEYARD Note: The image published herein has been reconstructed from a black-and-white original and may therefore contain inaccuracies regarding berry coloration.