A Century of Tropical Agricultural Research
A sample of tropical fruits some
of which are studied by scientist
|Tropical islands aren't just famous
for blue skies and emerald water. You can also find a profusion of tropical and
exotic fruits that can reawaken the senses.
For a century, USDA scientists at the Tropical Agriculture Research Station
(TARS) in Mayagüez, Puerto Rico, have been working to bring these tasty
fruits to consumers everywhere and make them available for centuries to come.
"One of our new projects is to introduce, preserve, and evaluate tropical
fruits that are economically important to the United States," says Ricardo
J. Goenaga, the head of TARS. "Changes in the U.S. population's diet and
an increase in the country's ethnic diversity have increased demand for
"Puerto Rico has 300 different soil series, representing 10 of 12 major
soil groups. Rainfall ranges from 35 inches in the southern semiarid region to
over 80 inches in the northeastern region. We can grow tropical crops in
different agroenvironments to determine where these crops grow best," says
Entomologist Randall Pingel
examines papaya fruits for
symptoms of papaya
|At various times, you'll find
familiar and uncommon crops being studied at TARS, including dry beans,
sorghum, banana, plantain, and exotic fruits such as rambutan, carambola (star
fruit), mamey sapote, lychee, longan, papaya, mango, and mangosteenalso
known as the "queen of fruits" for being one of the finest flavored
fruits in the world.
"Puerto Rican farmers have established about 2,000 acres of mango orchards
in response to increased demand for these fruits," says Goenaga.
"They are mostly exported to the U.S. mainland and Europe.
"Very little information is available on growing and managing tropical
exotic fruits. We're trying to find out what diseases and insects, as well as
physiological and environmental variables, affect their growth and yield
"We want to know which insects are problems, when they attack, and what
damage they cause," says ARS
entomologist Randall L. Pingel. "But this process takes time. Crops like
rambutan, sapodilla, and mangosteen take 4 to 8 years to bear fruit."
Sorghum flowers from various
accessions give geneticist John
Erpelding clues to sources of
resistance against sorghum ergot,
a major fungal pathogen.
|Tropical Plants from Afar
One of TARS' main goals during its first 40 years was worldwide tropical plant
collecting. Currently, about 2,000 species are growing at the station,
representing one of the best tropical plant collections in the Western
Hemisphere. Many of the crops are not native to this area, like rambutan from
southeast Asia or lychee from China. Exotic plants there include cinnamon,
nutmeg, rubber, vanilla, black pepper, citronella, camphor, teak, mahogany,
palms, and Manila hemp. Goenaga says the lab receives germplasm requests from
The facility is part of the U.S. National Plant Germplasm System (NPGS). It
introduces, maintains, characterizes, and evaluates germplasm collections of
banana, plaintain, sapodilla, mamey sapote, cacao, Garcinia, Annona, and
bamboo. Preserving these collections for future generations is extremely
important, says horticulturist Heber Irizarry, who is in charge of the
Geneticist James R. Smith
examines recently developed
bean lines resistant to common
|Irizarry's main research has been on
plantain and banana. There are 28 plantain and 83 banana accessions in the TARS
collection. TARS researchers have made a noteworthy contribution toward the
introduction, selection, and evaluation of superior plantain and banana clones
and the proper management of these crops under different environments.
TARS researchers are collaborating with other international institutions to
introduce and evaluate newly released black sigatoka-resistant plantain and
banana hybrids developed by the International Institute of Tropical Agriculture
in Nigeria, Africa, and for the Fundación para la Investigación
Agrícola in Honduras, Central America.
Black sigatoka, caused by the fungus Mycosphaerella fijiensis Morelet,
is the most destructive disease of plantain and banana. The fungus attacks
plant leaves, preventing the fruits from filling and causing drastic yield
reductions. Though the disease is not present in Puerto Rico, it is in some
neighboring Caribbean countries and has been reported in South Florida.
In Corozal, Puerto Rico, plant physiologist Ricardo Goenaga (foreground) and agronomist Edmundo Rivera collect carambola fruits to check for brix (sweetness) in a variety trial.
|Truly Diverse Beans and Grains
There are very few dry-bean breeders in the world, and ARS geneticist James R.
Smith is one of them. Smith has a fondness for beans, which are high in dietary
fiber, low in fat, and a good source of protein. He's responsible for the TARS
bean project, designed to improve bean germplasm by increasing genetic
"We are collaborating with researchers at Zamorano, a Pan-American School
for Agriculture in Honduras, to develop bean varieties resistant to common
bacterial blight," says Smith. "We are developing bean germplasm for
several different market classes, of which the United States has at least 10.
Typical uses for some of these market classes include dark red kidneys for
salad bars, small red beans for chili, navy beans for pork and beans, and
pintos for refried beans."
Horticulturist Heber Irizarry
(left) and technician Nicolas
Diaz discuss the ideal stage
for harvesting cacao pods.
|A problem with growing tropically
adapted beans in the temperate United States is that many tropical varieties
are sensitive to day length. Smith is trying to make valuable
photoperiod-sensitive tropical varieties less sensitive to day length so they
can be grown in the United States.
Germplasm research at TARS involves cereal grain crops, like sorghum and corn.
About one-fifth of the world's sorghum is produced in the United States on only
4 percent of the country's agricultural land. Sorghum is a major food crop in
Africa and Asia, but in the United States, the grain is used to feed livestock.
Two-thirds of ARS' National Sorghum Germplasm Collection is from Africa, and
some of the germplasm was obtained 100 years ago. The collection is stored at
Griffin, Georgia, and Fort Collins, Colorado, and contains more than 40,000
seed samples from 106 countries, including most African and Asian nations. TARS
geneticist John E. Erpelding is curator of the collection. His primary focus is
to identify useful genetic variation that can be used to develop new and
"I'm determining the characteristics for each accession. There's a
considerable amount of variability in sorghum," says Erpelding. "So
far, we have characterized more than one-third of the collection. Certain
characteristics are adapted to specific regions. For example, a compact flower
head is typically found in drier regions."
Sample of variation in the
TARS sorghum collection.
| Sorghum, related to corn, is a
tropical crop sensitive to day length. Most sorghums in the collection will not
flower in the United States because they require a shorter day length during
the growing season for floral initiation. Erpelding says he's transferring
genes that influence sensitivity to day length to increase the genetic
diversity of sorghum that can be grown in the United States. Since sorghum can
be grown during the winter in Puerto Rico under a shorter day length, it is
ideal for studying sorghums having potential use in the United States.
"A collection from Mali has recently been added to our sorghum
collection," says Erpelding. "This addition will aid in preventing
loss of valuable genetic material and will be useful to researchers
Also part of TARS is a research station nestled on St. Croix in the U.S. Virgin
Islands. Here, quarantined plant materials from many countriesmostly
sorghum, pearl millet, and maizeare brought from the National Seed
Storage Laboratory at Fort Collins via the Plant Germplasm Inspection Station
at Beltsville, Maryland. Materials are grown and characterized and their seed
regenerated and sent to plant-introduction stations for long-term storage and
distribution to breeders and other plant scientists.
Since materials are quarantined, they must be grown in isolation from
commercial agricultural plantings and certified to be free of potentially
harmful plant pathogens. "We follow very strict protocols to safeguard
against diseases," says Goenaga. An ARS and an Animal and Plant Health
Inspection Service plant pathologist check plants very carefully and certify
them free of diseases before they are released for domestic use.
TARS, whose main hacienda-style building was built in 1909, will celebrate its
100th anniversary this year. Over the years the station has released about 300
tropical plant lines and cultivars.
So what's in store for the next 100 years? "A new project to identify,
increase, and preserve disease-free cacao clones," says Goenaga. "Our
cacao collection dates back to the 1950s and contains 200 accessions. We're
collaborating with other ARS labs to study how much genetic diversity is in the
current collection and to identify high-yielding clones. If we find favorable
lines, we can distribute them to growers worldwide."
Future research will also focus on developing tropical fruit production systems
that aid growers in expanding the markets and marketability of these crops.
Goenaga says developing value-added products with increased shelf life and
nutritional quality is also important for these crops. He notes that molecular
biology techniques will facilitate genotypic characterization of germplasm in
the sorghum collectionone of NPGS' largestand development of new
dry-bean germplasm possessing multiple stress resistance for breeding programs
in the United States.By
Weaver-Missick, 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 Wold Wide Web at http://www.nps.ars.usda.gov.
The scientists mentioned in this story are with the USDA-ARS
Agriculture Research Station, 2200 Pedro Albizu-Campos Ave., Suite 201,
Mayagüez, PR 00680-5470; phone (787) 831-3435, fax (787) 831-3386, e-mail
"A Century of Tropical Agricultural
Research" was published in the
issue of Agricultural Research magazine.