New Crops: Peppermint and Grapefruit
In the 1950’s, plant breeders became interested in using
radiation to improve cultivated plants. After irradiation, the
number of variations can be dramatically increased, making it
possible to trigger more variants in one season than might be seen
in a lifetime under normal conditions.
BNL initiated a cooperative program in which dozens of
organizations sent plant seeds and vegetative grafting stock to the
Laboratory for irradiation by various methods, including the Gamma
Field, the Graphite Research Reactor and
special irradiation chambers. After the material was exposed, it was
returned to the home organization for propagation and mutation
screening. The organization then tracked mutations that appeared
useful.
Aside from the color and size changes that were achieved in a
number of ornamental plants, an outstanding success story of this
program concerns peppermint.
Some years ago, the sole source of peppermint oil in the U.S. was
the Mitcham variety, until it fell to a wilt disease caused by the
verticillium fungus.
Soil fumigation and crop burning were only partially successful
in reducing the incidence of this disease. Attempts to produce
disease-resistant varieties by cross-breeding failed because those
varieties that resisted the fungus always suffered an unacceptable
change in the oil flavor.
In the late 1950’s, a visiting researcher from a large
mint-producing company, participating in Brookhaven’s cooperative
program, grew a number of viable plants from irradiated stock. One
of these was a disease-resistant mutant that maintained the original
flavor of peppermint oil. This mutant is now in general use.
The savings achieved through its introduction amount to millions of
dollars yearly. And what American child has not chewed peppermint
gum!
Another practical result of the BNL irradiation program is
gourmet grapefruit – Star Ruby and Rio Red.
In the late 1950’s, a Texas citrus grower found a natural
mutation on a Foster Pink grapefruit tree. Called Hudson Pink, the
fruit was sweet and red, but contained a lot of seeds.
In 1959, the Texas A&I University Citrus Center sent to BNL more
than 3,000 Hudson Pink seeds for irradiation. Six seeds produced an
almost seedless grapefruit with peel an orange-red color and juice
the color of ripe tomatoes. From these, one was selected that
consistently produced the fruit with the fewest seeds. This was the
Star Ruby grapefruit – a brilliant, red grapefruit with a higher
sugar and citric acid content than its predecessors.
Budwood was made available to nurseries in 1970, and Star Ruby
was planted in several locales. It does not thrive in all locations,
and yield is variable. Still, the trees are reported to do well in
California and Israel. Although production will always be limited,
the Star Ruby does have consumer appeal as a gift fruit because of
its rich red color.
Another grapefruit, however, seems destined for the mass market.
In 1963, the Texas Citrus Center had BNL irradiate budwood from a
planting of the popular Ruby Red grapefruit. The budwood was
propagated on rootstock, and several years later, one of those trees
grown from irradiated budwood produced fruit with flesh three times
redder than the Ruby Red. In 1971, this particular tree was
propagated and ten trees placed in a test planting. In 1976, the
careful nurturing and tracking of the original budwood finally paid
off. A natural mutation was discovered on a limb of one of the ten
trees. This mutation, named Rio Red, produced fruit with flesh color
nearly as red as Star Ruby (five times redder than Ruby Red),
although the peel doesn’t have such a deep blush.
Rio Red budwood was released to growers in 1984. While it’s too
soon to tell, Rio Red will likely become popular, both among citrus
growers and consumers. Taking after Ruby Red, it is less finicky
about growing conditions. Given no unexpected production problems,
it will find its way onto more and more breakfast tables.
The success story of Star Ruby and Rio Red grapefruit may be
appended someday. In 1986, the Texas Citrus Center sent to the
Laboratory orange budwood, which was irradiated in the Medical
Research Reactor. Years from now, we may see the payoff.
- Excerpted from "The First Forty Years, Brookhaven National
Laboratory, 1947-1987"
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