Viticulture research at California State University, Fresno suggests a strong market potential for two table grape varieties recently introduced to commercial growers.

Autumn Royal and Sweet Scarlet were introduced through a long-term table grape development program operated jointly by Fresno State and the U.S. Department of Agriculture. Leading the program are Fresno State viticulture professor Sayed Badr and USDA geneticist David Ramming. The pair has collaborated on the development of other table grape varieties including Crimson, Princess and Summer Royal. Ramming's specialty is breeding for desired characteristics and Badr's is evaluating viticultural practices.

In today's breeding programs, care must be taken develop a varieties that not only appeal to consumers' taste preferences, but fit well into retail marketing strategies, Badr explained

“Retailers like to have a mix of colors in their table grape displays, such as red, green, and black. A good display of colors has eye appeal to consumers,” he said. Timing is also a key element in marketing. Newer varieties have the best opportunity for success if they ripen later or earlier than existing popular varieties — that way retailers have a continuous supply of California-grown, good tasting grapes that are available through the summer and fall months.

Of the several varieties Badr and Ramming have been testing, Autumn Royal is growing in popularity because it is seedless, has a large berry, a neutral flavor, and it comes in at the right time in the marketplace, Badr said.

Production trials at the Fresno State campus vineyards have shown that the Autumn Royal grows well in the San Joaquin Valley — so well in fact that limiting vine production is crucial for producing a high-quality crop.

“With over cropping we can delay fruit maturity, inhibit color development, and reduce berry size and sugar levels,” Badr said. “So you can have a large crop, but the quality tends to go in the other direction.”

“For Autumn Royal we are recommending quadrilateral training with spur pruning five to seven spurs per cordon and one to two nodes per spur,” Badr said.

While Autumn Royal is a late-maturing variety, Sweet Scarlet is a mid-to-late season red grape that has become popular among retailers and consumers since its release in 2003.

“It has a special flavor, a light to medium Muscat flavor with a pleasing aftertaste,” Badr said. And because of its color and earlier maturity, it tends to compliment rather than compete with the black Autumn Royal.

Viticultural research trials on Sweet Scarlet over the last three years have focused on the effect of pruning methods, gibberellic acid (GA) application and girdling on yield and fruit quality. Different treatment combinations produced varying effects on berry size, weight, and titratible acidity, Badr noted.

“Girdling or GA alone caused a slight increase in berry weight or size. However, girdling plus GA at 20 or 40 mg/L significantly increased berry weight and berry size.”

The results should be valuable to growers, not as exact prescriptions, but as guides for leading to optimum production, Badr emphasized.

“Every vineyard has its own climate, soil, and rootstock conditions. That's where the variability comes in. the grower has to fine tune these practices depending on his particular vineyard conditions,” he said.

Details of the viticultural trials for both Autumn Royal and Sweet Scarlet are available in poster presentations on display at Fresno State's Viticulture and Enology Research Center (VERC). Complete written reports are to be released later this year. Call the VERC library at 559-278-2089 or visit the website at http://cati.csufresno.edu/verc for more information.