I. INTRODUCTION
Alfalfa (Medicago sativa L. sensu
lato) is the most important forage legume species in North
America. The area of alfalfa cut for hay in the U.S increased
from a few ha in the mid-1800s to a peak of 12.1 million ha in
1958. Since 1980, the area has varied between 10.5 and 10.9 million
ha. The crop has an estimated market value of about $7.5 billion.
Compared with all other crops, alfalfa is recognized as the most:
In addition, alfalfa is an excellent
source of vitamins and minerals for all classes of livestock and
is important for improving soil tilth. It also serves as a model
system in many types of forage crop research and for the study
of autotetraploid inheritance (Barnes et al., 1988). Many annual
species in the genus Medicago serve as important components
in pastures in regions with Mediterranean climates. Potential
use of annual Medicagos in the U.S. remains to be determined.
However, they may be particularly well suited for use as pasture,
green manure, and cover crops in sustainable agricultural systems.
II. HISTORY, USE, AND STATUS OF VULNERABILITY
OF MEDICAGO SPECIES
Origins of alfalfa and its early
introductions in North America
Alfalfa originated in Vavilov's "Near
Eastern Center"--Asia Minor, Transcaucasia, Iran and Turkistan.
In the wild, M. sativa and related perennial species are
found throughout Eurasia and as far north as Siberia. Alfalfa
spread from its center of origin into Europe, North Africa, Arabia
and eventually South America with invading armies, explorers,
and missionaries as feed for horses and other livestock. In 1736,
European colonists brought alfalfa to the eastern U.S. where the
crop was referred to by its European name, lucerne. These introductions
generally were not successful, except for a few planted on well-drained
limestone soils. Alfalfa was well suited to the dry climates and
irrigated soils of the western U.S., where it was introduced from
Mexico by Spanish missionaries as early as the 1830s. Alfalfa
eventually spread eastward to the Intermountain region and the
southern Great Plains. Movement into areas with severe winters
was limited by the lack of hardiness in the primarily Spanish-derived
germplasm. The introduction of winter-hardy types from northern
Europe to the North Central States in the 1850s allowed successful
alfalfa culture in the colder and more humid areas of the midwestern
and northeastern U.S.
Plant introduction and alfalfa
improvement
From alfalfa's initial introduction
until 1955, about 33 recognized alfalfa cultivars or regional
strains were grown in the U.S. and Canada. About half of these
were directly introduced from Europe, Asia or the Near East. Between
1958 and 1991, organized alfalfa breeding expanded tremendously
and the number of recognized cultivars increased to about 400.
Before 1925, most alfalfa breeding efforts in North America were
directed toward selecting strains that were more winterhardy.
During the next 30 years, emphasis was placed on developing cultivars
that combined winterhardiness and resistance to bacterial wilt.
During the late 1950s, the emphasis was placed on developing cultivars
resistant to other diseases and several insect pests (Barnes et
al., 1988).
A trend toward increased genetic diversity
in alfalfa cultivars, spurred largely by breeding efforts begun
in the 1950s, and the inherent genetic heterogeneity of the species
has made alfalfa less vulnerable to catastrophic loss than it
was 50 years earlier. Nevertheless, relatively few individual
sources of germplasm have been exploited in alfalfa breeding and
genes from a single accession have frequently been used repeatedly.
For example, a single introduction (PI 20725) is represented in
at least 30 distinct, and widely grown cultivars (Rumbaugh, 1991).
All basic germplasm used in the development of present North American
alfalfa cultivars can be traced to one or more of nine primary
regional germplasm sources (Barnes et al., 1977). However, several
of the nine regional sources have been represented by very few
introductions. Most notable in this regard is the predominance
of a small number of closely related 'African' and 'Indian' introductions
within elite nonhardy cultivars (Smith et al., 1991). Furthermore,
in some regions sources of exotic alfalfa germplasm, which may
be useful in plant breeding, are subject to loss due to the importation
of elite cultivars, principally from the U.S. (Marble, 1989).
Annual species of Medicago--the
"medics"
The genus Medicago also includes
many lesser known, but potentially useful annual species. Members
of the 29 annual Medicago species, commonly known as "medics",
are receiving more attention with the emphasis on more sustainable
agricultural systems. Medics are native to semiarid areas around
the Mediterranean Sea and have long been used in unimproved pastures
in the region. Many medics are now widely distributed throughout
the world, largely in areas with mild, rainy winters and alkaline
soils. In these regions, medic seeds germinate in late fall with
the onset of winter rains, grow vegetatively until early spring,
and then flower and produce seed in late spring before the plant
dies. Hardseededness is common in medics reducing premature germination
during summer months. Many medics are tolerant of grazing and
can produce multiple forage crops in a single season. Medics have
been extensively utilized in Australia and are grown on about
50 million ha there (Crawford et al., 1989). Medics have been
most successful in cereal-legume crop rotation systems in southern
Australia where winter rainfall averages between 250 and 500 mm.
Certain medics have also been used in revegetation, intercropping,
hay production or as green manures. The U.S. PI collection now
contains over 2000 accessions of annual medics. These introductions
originate from a wide variety of environments and represent a
tremendous source of potentially useful plant materials for use
in sustainable agriculture.
III. PRESENT GERMPLASM ACTIVITIES
The roles of public and private
alfalfa researchers
The rate of release of new alfalfa cultivars
in the U.S. has increased steadily over the last 90 years. About
one cultivar was released every three years between 1901 and 1940;
one each year between 1941 and 1960; about 17 per year between
1981 and 1985; about 30 each year between 1985 and 1990; and about
60 per year between 1990 and 1995. Since their inception in the
mid-1950s, private alfalfa breeding programs in the U.S. have
been responsible for the rapid increase in numbers of recognized
alfalfa cultivars. During the period between 1955 and 1960, approximately
20% of cultivars were released from private breeding programs.
This proportion increased to more than 95% between 1985 and 1990.
Private breeding programs increased in number, size and sophistication
from about 1965 to 1985. During the late 1980s, competition for
market share caused several mergers within the private sector.
At present, there are about 8 commercial alfalfa breeding programs
with annual research expenditures ranging from about $100,000
with 1.0 scientist-year (SY) to more than $2 million with five
or more SYs.
Increased breeding by industry was accompanied
by a reduction in the number of public breeding programs, and
by a change in the direction of public research from breeding
new cultivars to developing new breeding procedures and improved
germplasm (Barnes et al., 1988). The transition from applied alfalfa
breeding to more fundamental research within public agencies contributed
to the development of several comprehensive research efforts.
Examples of research areas include: study of the morphology and
anatomy of alfalfa as it relates to productivity and persistence,
improvement of nitrogen fixation, improvement in grazing tolerance,
transfer of genes between ploidy levels and Medicago species,
development of methods to maximize heterosis for yield, improvement
of forage quality by improving nitrogen concentration in the forage,
elevating insect resistance by using novel methods of insect inhibition,
development of genetic maps using molecular genetic markers, description
of phenotypic and genetic relationships between different alfalfa
germplasm sources, transformation of alfalfa with foreign genes,
and use of tissue culture in selection programs. More generally,
public researchers working with alfalfa also continue to provide
valuable knowledge in plant genetics, physiology, and growth,
including resistance to biotic and abiotic stresses.
The increase in private commitment to
alfalfa improvement has been associated with a concomitant the
decline in the number of public alfalfa researchers. The wide
acceptance of the best proprietary cultivars by the 1980s confirms
the efficacy of private breeding programs, and suggests that an
appropriate balance has been reached between fundamental public
research and more applied private research. However, the balance
between public and private programs may now be in danger because
of recent reductions in support for public alfalfa research programs.
The termination of a number of public alfalfa breeding and genetics
programs also means that many breeder's germplasm collections
may be subject to loss.
Increasing the use of medic germplasm
Annual Medicagos have not been
used as intensively in agriculture in the U.S. as in Australia
or the Middle-East. Naturalized medics are most common in California
where ecotypes of M. polymorpha, known locally as bur clovers
are most frequent. They fix nitrogen and produce high protein
forage on many winter rangelands in some of the drier areas of
the state. Bur clovers are also found in the pastures of east
and central Texas and southern Oklahoma. The medic species M.
orbicularis (button clover) and M. arabica (spotted
bur clover) have been introduced into the southeastern U.S. where
they were overseeded into grass pastures. Research in Montana
and Utah indicates that certain medics such as M. lupulina
may also hold promise as summer annuals on pastures and rangelands
in the Great Basin (Rumbaugh and Johnson, 1986). A cultivar of
M. lupulina has been released by the Montana State Agricultural
Experiment Station (Sims et al., 1985). The use of annual medics
as summer green manure crops has been investigated extensively
in the north central and northeastern US since the early 1990s.
Over 20 medic cultivars from seven different
species have been released by Australian plant breeders. Their
improvement has focused on earlier flowering, reduced pod spininess,
increased forage and seed production, and tolerance to insects.
Intensive efforts have also been directed toward the development
of medics and their associated Rhizobium bacteria. While
medics cannot be directly hybridized with their perennial relative
alfalfa, research on transferring certain traits, such as resistance
to some insects from medics to alfalfa is also now underway. Until
the early 1980s, relatively little research has been conducted
with annual Medicagos in the U.S. The ACGC is actively
working to promote the recognition and use of medics, especially
as part of sustainable agricultural systems. A short article describing
the range of variation in the medics and their possible uses was
distributed by the ACGC in early 1991 and has appeared in various
publications oriented toward farmers and ranchers.
IV. ACGC ACTIVITIES SINCE 1991
The present ACGC committee contains
20 members fairly equally divided between the public and private
sectors (Appendix A). From 1991 to 1995, Steve Smith served as
chair. Joe Bouton is the current chair.
In 1976, the U. S. PI collection had
about 900 accessions of Medicago sativa and M. falcata
plus several hundred accessions of annual and related perennial
Medicago species. At that time there was no systematic
plan for seed increase under isolation and most evaluations were
made with open-pollinated seed. There was no national program
for germplasm evaluation or germplasm enhancement and few plant
breeding programs were concerned with using P.I.'s. Since then,
alfalfa scientists individually and collectively with the NPGS
have developed a functional system for germplasm collection, maintenance,
and evaluation. Most parts of the system are now in place. ACGC's
present concerns involve refinement of the collection as well
as preservation and evaluation of parts of the system, and development
of a germplasm enhancement program to make basic germplasm more
useful to the alfalfa research community.
Collection Management
Plant exploration and collection trips
made by D. Johnson and D. Sheely to Mongolia and by Stephanie
Greene et al. to the North Caucasus Mountains, Russia resulted
in the addition of several new accessions of both perennial and
annual Medicagos.
These recent acquisitions have increased
the collection to about 2936 accessions of perennial Medicagos
and 2613 accessions of annual Medicagos (Appendix B). Since
one of the committee's main objectives has been to regenerate
seed of each of these accessions in cage isolation (e.g. to move
away from open-pollinated seed), a current inventory shows that
only 417 accessions of perennials and 406 accessions of annuals
still require this type of seed increase (Appendix B).
Medicago accessions were distributed
as follows:
FY1991 FY1992 FY1993 FY1994 FY1995 Perennials 2139 1520 1409 1016 2518
Annuals 2858 1780 1079 991 1319
With the recent evaluations for ruminal
protein degradation, unifoliolate internode length, and tolerance
to lygus, Sclerotinia, and acid soils, data are now available
in the Germplasm Resources Information Network (GRIN) for over
35 agronomically important traits for the core collection, and
for many traits, a large portion of M. sativa accessions
in the collection. Basic agronomic data on annual medics are also
available from seed increase plots as well as the addition of
anthracnose evaluation on the annual core collection.
Evaluation Proposals
The committee decided to solicit and
fund proposals on evaluation of the collection from the alfalfa
community. In the initial year (1995), 14 proposals were received.
Nine reviewers were selected from the committee with a majority
of these from the alfalfa seed industry. The top 4 proposals were
funded and included enhancement of Medicago germplasm for
resistance to multiple virulence phenotypes of Aphanomyces root
rot, enhancement of M. falcata germplasm for use in cultivar
development, measuring genetic distances among accessions in the
core collection, and evaluation of the collection for glandular
trichome density and alfalfa weevil resistance. The committee
plans to continue this "granting" program for the immediate
future.
Curation
Dr. Stephanie Greene began as Alfalfa
Curator at Pullman in January 1995. Dr. Greene will concentrate
on regeneration and curatorial activities along with organization
of evaluation data, user support and research on regeneration
techniques. An immediate goal was to update and clarify the accession
histories so duplicate accessions may be eventually eliminated.
To date, 12,000 accession histories have been completed, and of
these, 500 have been entered into GRIN. Once completed, the GRIN
data base will be carefully reviewed for duplication based on
accurate passport information. Dr. Greene expects to complete
this project by the end of 1996.
Communications
One of the ongoing objectives of the
ACGC is to improve the user community's understanding of the resources
held within the collections. In 1993, ACGC developed and distributed
the first Medicago Germplasm Newsletter to members of the
NAAIC in the U.S (Appendix C). The costs of the bulk mailing were
covered by the NAAIC. A second volume of the newsletter was produced
and distributed in 1994 and the committee plans to continue this
activity in the future.
Enhancement
The current PI collection of perennial
Medicago species is large and few accessions have many
of the basic traits necessary in current varieties. The disparity
in pest resistance between current alfalfa cultivars and essentially
all PI's makes the use of the collection difficult in applied
alfalfa breeding. Recognizing this, the ACGC has in the past considered
funding development of regional and national germplasm pools for
perennial Medicagos utilizing both plant introductions
and elite germplasm (see 1991 report). Budget constraints and
the lack of this objective being a high priority for the committee
resulted in the enhancement plan never being implemented. However,
this will be changing with the funding of two proposals concerning
enhancement (see Evaluation Proposals section above) and indicates
the alfalfa community considers specific enhancement proposals
more desirable and workable than development of regional germplasm
pools.
The ACGC has not developed an enhancement
plan for the annual Medicagos.
V. RECOMMENDATIONS
1. Continued funding for the alfalfa
germplasm CRIS project at Pullman, WA for the preservation of
the current Medicago collection with annual assignment
of activities by the ACGC and for continuation of the current
evaluation "granting" program with an increased emphasis
on the development and refinement of core collections .
2. Implement a germplasm enhancement
plan that includes participation by public and private breeding
programs.
3. Develop a thorough exploration and
collection plan based on recognized deficiencies in the U.S. PI
collection and other collections including standards to reduce
redundancy.
4. Generate a plan to catalog and facilitate
the distribution and preservation of germplasm held in breeder's
programs that are being discontinued.
Considering the funding currently available
from the USDA for alfalfa germplasm preservation and evaluation
research, it seems unrealistic to request new funds. However,
the committee is greatly concerned with the transfer of the Trifolium
collection to Pullman without the funds normally associated with
the Trifolium collection. This move effectively reduces the budgets
available to manage and evaluate both collections. Therefore,
ACGC considers restoration of these moneys to be critical in order
to properly manage, evaluate, and enhance both the Medicago
and Trifolium collections.
VI. REFERENCES
Barnes, D.K., B.P. Goplen, and J.E.
Baylor. 1988. Chapter 1: Highlights in the USA and Canada p. 1-24.
In A. A. Hansen, D. K. Barnes, R. R. Hill, Jr. (ed.) Alfalfa
and Alfalfa Improvement. ASA/CSSA, Madison, WI.
Barnes, D.K., E.T. Bingham, R.P. Murphy,
O.J. Hunt, D.F. Beard, H.H. Skrdla, and L.R. Teuber. 1977 Alfalfa
germplasm in the United States: genetic vulnerability, use, improvement,
and maintenance. USDA Tech. Bull. 1571. U. S. Government Printing
Office, Washington, D. C.
Crawford, E.J., A.W.H. Lake, and K.G.
Boyce. 1989. Breeding annual Medicago species for semiarid
conditions in southern Australia. Adv. Agron. 42:399-437.
Guarino, L. 1990. Alfalfa collecting
in southern Arabia. Plant Genetic Res. Newsl. 80:33-35.
IBPGR. 1985. Forages for Mediterranean
and adjacent arid/semi-arid areas. Report of a working group,
April, 1985. IBPGR Secretariat, Rome.
Marble, V.L. 1989. Fodders for the Near
East: Alfalfa. FAO Plant Prod. and Protect. Paper 97/1. FAO, Rome.
Rumbaugh, M.D. 1991. Plant introductions:
The foundation of North American forage legume cultivar development.
p. 103-114. Use of Plant Introductions in Cultivar Development,
Part 1, CSSA Spec. Pub. no. 17.
Rumbaugh, M.D. and D.A. Johnson. 1986.
Annual medics and related species as reseeding legumes for northern
Utah pastures. J. Range Manage. 39:52-58.
Sims, J. R., S. Koala, R. L. Ditterline,
and L. E. Wiesner. 1985. Registration of 'George' black medic.
Crop Sci. 25:709-710.
Smith, S.E., A. Al-Doss, and M. Warburton.
1991. Morphological and agronomic variation in North African and
Arabian alfalfas. Crop Sci. 31:1159-1163.
Updated June 24, 1996.