Archived Issues

Low conversion

As early as 1999, the tobacco industry took steps to reduce the level of tobacco-specific nitrosamines (TSNAs), carcinogens found to be particularly high in U.S. flue-cured and burley tobaccos, as well as tobaccos in Canada and parts of Europe. Reducing flue-cured TSNAs proved to be relatively simple. Reducing TSNAs in burley, however, proved to be trickier.

Matt Mullen

A problem and a solution
In tobacco, nicotine can lose a methyl group in a process called demethylation, or conversion, to form nornicotine. Many burley tobacco plants convert a substantial proportion of their nicotine to nornicotine during curing. Nitrogen oxides in the atmosphere sometimes react with nornicotine to form compounds known as nitrosonornicotines during curing, and nitrosonornicotines are the major TSNA in burley tobacco.

Fortunately, within populations of burley tobacco plants, there are certain plants that convert nicotine into nornicotine at very low levels. And low levels of nornicotine mean fewer of these molecules will be converted to TSNAs during curing. These types of plants are known as low converters.

Seed breeders knew if they eliminated the mother plants that converted nicotine at a high rate in seed lots—a process known as “screening”—most of the seed produced from the remaining mother plants would therefore be of the low-converting type.

The LC ProtocolSeed companies and university breeding programs have developed a number of techniques to identify high-converting plants, but the process is slow and labor intensive. A more promising technique has emerged from research at the University of Kentucky (UK) in Lexington, Ky.

Anne Jack is a tobacco research specialist at UK. Formerly the head of plant breeding at the Tobacco Research Board in Zimbabwe, Jack has been instrumental in developing a program to certify seed as low converting, known as the UK LC Protocol.

The LC Protocol calls for breeders to use ethephon, a chemical sometimes used to accelerate ripening of fruits and vegetables. Burley tobacco plants have a gene that controls the amount of nicotine that will be converted into nornicotine. Dipping the leaves in a solution of ethephon “forces” the gene in the leaf to express its full potential and makes it possible to cure young leaves, which breeders can then test a month after transplanting. The high-converting plants can then be eliminated from seedlots before they flower. Starting in September, the
LC Protocol became available at www.uky.edu/
Ag/Tobacco.

So what’s the difference between seed screened for low-conversion plants and seed that bears the LC suffix? Currently, LC designates that the seed has been screened using the official UK protocol, and the breeders of the seed have applied to their respective state commissions to release the LC seed as a completely new variety. Seeds produced according to these procedures can bear the LC suffix after the variety name, for example: TN-90LC.

In other words, all LC seed has been screened, but not all screened seed will necessarily bear the LC suffix. “Seed that has been screened just means that the seed has been screened with a method,” Jack says. “That’s not to say that other methods don’t work, however.”

All of the seed coming out of UK breeding programs from now on will bear the LC suffix. UK has also developed a logo for seed that originated from its breeding programs and has gone through the LC screening process under UK’s supervision.

Moving quickly
According to a summary of U.S. burley tobacco marketing contracts published by UK in 2005, Philip Morris, Universal and R.J. Reynolds all specifically mandate that growers use screened or LC seed varieties.

Development of the LC Protocol moved quickly. Gary Palmer, UK burley tobacco specialist, says the development of the LC Protocol “was a monumental task, but we’ve managed to do this transition in three years.”

And though industry needs demanded a quick transition, growers shouldn’t even know the difference between LC-designated seed in the fields, Palmer says. “Hopefully, the farmer won’t even notice. TN-90LC should perform exactly like the old TN-90.”

Tobacco companies and leaf dealers continue to boost demand for the LC seed, says Sam Baker, vice president of Cross Creek Seed in Raeford, N.C., and Cross Creek Sementes do Brasil in Santa Cruz do Sul, Brazil. “Everybody internationally is clamoring for it right now,” Baker says. “Philip Morris started requesting LC, and everybody else seemed to follow.”

Many seed companies are moving to clear out their inventories of screened seed and migrating to LC. “It’s mainly domestically [in the U.S.], but it’s beginning to take hold internationally as well,” says one U.S.-based seed merchant. “It’s not required internationally, but we as a seed company are migrating to all LC.”

According to Humberto Alba, president of F.W. Rickard Seeds, TN-90 had been the bestseller in the burley market until KT 204LC was introduced in 2005. In 2006, KT 204LC overtook TN-90 as the bestseller in the burley market. “The University of Kentucky did a very good job of disseminating information about the outstanding characteristics of this new variety, and it overtook TN-90 in the marketplace in less than two years,” Alba says.