...From the pages of Agricultural Research magazine
From Hawaii to
Plant physiologist Paul Moore examines coffee trees involved in genetic studies on the Island of Oahu.
You're relaxing at a neighborhood
café, savoring a cup of your favorite roast and a decadent slice of
chocolate macadamia nut torte. The tropical beans used to brew your coffee and
the rich, buttery nuts embedded in the torte may have come to you from the
farms of the sunny Hawaiian Islands.
Scientists with the ARS U.S. Pacific
Basin Agricultural Research Center in Hawaii, and their colleagues, are
discovering more about the genetic makeup of these exotic tropical crops. Their
research should benefit not only growers, but also coffee lovers and macadamia
One of the scientists' goals is to ensure that the genetic diversity, or gene pool, of both crops is preserved for the future. For example, as-yet-unknown genes in today's popular commercial coffee varieties or in their wild, uncultivated relatives might hold the key to innovative new coffees for tomorrow. In the case of macadamia, the investigations could streamline breeding of superior trees that boast genes for bigger yields of this premium nut.
In preparing to identify
potential causal agents of
grey kernel disease of
macadamia, plant pathologist
Lisa Keith examines
macadamia nuts for
hairline cracks, which seem
to be necessary for symptoms
A Little History
Macadamia nut and coffee plants sailed into Hawaiiliterallyin
the 1800s. Hawaii was an important stopping point for sailors to restock
provisions needed for their long voyages. Though macadamia devotees may find it
hard to believe, macadamia trees were first imported into Hawaii for
landscaping and establishing pleasant woodlands, and only later were cultivated
for their tasty, unusual nuts.
Coffee was first transported to the Hawaiian Islands via a British gunship
that was carrying home the bodies of King Kamehameha II and Queen Kamamalu, who
had died of measles during a state visit to London. The ship took coffee trees
aboard during a stopover for supplies in Rio de Janeiro. The rest is
Both coffee and macadamia flourished in Hawaii's mild climate. Today, macadamia nutsknown as "mac nuts" to island localsare grown mainly on the Big Island of Hawaii, while coffee is produced throughout the Hawaiian Islands, earning them their nickname "America's Coffee Islands."
Macadamia nuts, from
Uncovering the Beans'
To discover more about coffee and macadamia nut genetic material, the
researchers are examining the makeup of specific stretches of DNA. Snipping
corresponding stretches from each of the individual species ensures a stable,
valid basis of comparison. Any dissimilarities among the DNA samples could be
important, helping reveal the location of interesting genessuch as one
that makes a particular species more hardy or flavorful than others.
Coffee plant leaves used for the tests came from a genebank assembled by
University of Hawaii scientists and maintained by the grower-sponsored Hawaii
Agriculture Research Center, based at Aiea. The researchers analyzed three
coffee species from Africa, the likely origin of coffee. Coffea arabica,
the source of today's premium beans, and C. canephora, known for the
robusta beans commonly used for making instant coffees, are the two most widely
grown coffees in the world. C. liberica is grown commercially in the
Philippines as well as in parts of Africa.
When researchers compared these species, they found significant variation: C. arabica, for example, was about 50 percent different from C. canephora and C. liberica. Says ARS plant physiologist Paul H. Moore, "The beans from these species make very different brews. The species grow at different elevations and differ in their resistance to pests. Perhaps some of those differences are reflected in the variations in the genetic material that we examined."
One of 43 macadamia
accessions maintained as
field plantings at the
U.S. Pacific Basin
Agricultural Research Center,
in Hilo, Hawaii.
Nearly all the C. arabica varieties examinedBourbon, Catimor, Catuai, Caturra, and Mokka Hybridwere, on average, 93 percent similar among the stretches of DNA analyzed. Catimor and Mokka Hybrid differed the most from each otherinformation that could eventually result in a better cup of joe.
Probe Zeros In on Mac Species
America's official macadamia nut genebank at Hilo, Hawaiiabout 45
minutes by plane from Honoluluprovided leaf samples for the macadamia nut
study. ARS horticulturist Francis T.P. Zee manages the collection, which
includes macadamia nut types grown in Hawaii, California, Australia, South
Africa, and Thailand.
The macadamia nut study is helping to clarify key genetic differences among
four of the world's seven macadamia species, as well as a wild relative with
the evocative name "rose nut," or Hicksbeachia pinnatifolia.
Of the five species examined, only Macadamia integrifolia and M.
tetraphylla bear edible nuts; M. ternifolia, M. hildebrandii,
and rose nut do not.
Scientists found that the two macadamia species that produce edible nuts
were the most similar to each other. According to plant molecular geneticist
Ray Ming of the Hawaii Agriculture Research Center, who led the investigation,
macadamia nut species were, on average, about 26 percent different. This is a
relatively high level of genetic diversity and means there's enough variation
to breed unique new nuts for Hawaii's orchardsa boon for mac nut lovers
around the world.
These studies are the most comprehensive genetic analyses to date of cultivated arabica coffees and cultivated macadamia nut varietiesand the first to use a sophisticated laboratory technique called AFLP (amplified fragment length polymorphism). Delving even further into the variations among and within macadamia nut and coffee species may lead scientists to genes that control desirable traits, enabling future advances that may make your coffee and torte that much more delectable.By Marcia Wood, Agricultural Research Service Information Staff.
This research is part of Plant, Microbial, and Insect Genetic Resources,
Genomics, and Genetic Improvement, an ARS National Program (#301) described on
the World Wide Web at www.nps.ars.usda.gov.
Paul H. Moore is with the
USDA-ARS U.S. Pacific Basin Agricultural
Research Center, Tropical Plant Physiology, Disease, and Production Unit,
99-193 Aiea Heights Drive, Aiea, HI 96701; phone (808) 486-5411, fax (808)
Francis T.P. Zee is with the
USDA-ARS U.S. Pacific Basin Agricultural
Research Center, Pacific Basin Tropical Plant Genetic Resource Management
Unit, P.O. Box 4487, Hilo, HI 96720; phone (808) 959-5833, fax (808) 959-3539.
"Forum" was published in the June 2004 issue of Agricultural Research magazine.