Original varieties contaminated; new ones are virus-free

By Robert Burns
Texas AgriLife Research Center

One of the newest Texas Super­stars, virus-free Blue Princess verbena is not like other princesses, said the executive director of the Texas Superstar board.

For one thing, the Blue Princess likes the heat; in fact, it thrives on the Texas summer sun, said Dr. Brent Pemberton, Texas AgriLife Research horticulturist. And the same goes for its sister plant, virus-free Rose Princess verbena, which was also named a Texas Superstar for 2010.

“Most people make the mistake of pampering it,” Pemberton said. “It must be planted in the sunniest, best-draining spot in your landscape. It will not bloom profusely unless the plants get plenty of sunlight.” Plenty of sunlight means eight to 10 hours a day of direct ‘sunbathing sunlight,’” he said.

To produce virus-free stock, plants are carefully selected that have no disease symptoms. Once these plants are identified, they are grown in their own individual plots under “protected” conditions, Pemberton said.

Using virus-free stock for cuttings is not a new thing. The practice dates back to the beginning of the last century. “If they’re not virus-free, they don’t bloom and perform nearly as well as they do if they are virus-free,” Pemberton said. “You don’t do as well when you’re sick as when you’re healthy and well, and it’s the same for plants. This is true of roses and everything else. They’re just weaker if they’re infected.”

The resulting stock, called the “mother stock,” is continually monitored for disease symptoms, and any suspects are discarded. Cuttings are taken from the mother stock and increased. This process of selection may take years. From these increases more cuttings are made and the plants are sold to commercial growers.

The original Blue Princess verbena Texas Superstar was brought back from the United Kingdom by Greg Grant, a former AgriLife Extension horticulturist,  now with Stephen F. Austin State University.

Grant, working with other AgriLife Extension and AgriLife Research horticulturists, made selections from the English stock that were adapted to the hot conditions of Texas.

“You wouldn’t think a plant that came from foggy old England would be adaptable to the hard and mean
conditions of Texas, but it was,” Pemberton said. “We suspect, but we don’t know, that it was so because it was originally brought to England from South Africa.”

Not only is Blue Princess verbena heat tolerant, it is also more cold tolerant and produces larger flower heads than any previously available verbena. The original was also more disease and insect tolerant as well, which lead to its nomination as a Texas Superstar.

When first named a Texas SuperStar in 1998, the Blue Princess was virus-free, but the virus-free condition became a kicker. A few years later, the original Blue Princess mother stock became contaminated. A seedling selection from Blue Princess named Dark Lavender Princess was found and grown in virus-free conditions before it could be contaminated. The virus-free variety was eventually sold as Blue Princess, Pemberton said.

Both verbenas produce brilliant blooms, and while they need not be pampered, keeping them bright and beautiful requires discipline on the part of the gardener. Many gardeners are hesitant to prune the plants when there are still blooms, Pemberton said.

“After the first spectacular bloom display, cut-shy people will be looking at ugly for the rest of the season and wondering why,” he said. Pemberton’s advice to gardeners is to perform a light pruning after the first abundant blooms, when the plant appears to be shutting down. This will produce another lush crop of flowers.

“People who cannot discipline themselves to shear old blooms periodically should not grow verbena,” he said.

Texas Superstar is a registered trademark owned by Texas AgriLife Research. More information about the Texas Superstar program can be found at texassuperstar.com/.