THE CASSAVA MOLECULAR DIVERSITY NETWORK MOLCAS

1
THE CASSAVA MOLECULAR DIVERSITY NETWORK (MOLCAS)
1Fregene M., 2Rosling H., and 3Akerbolm M. 1.
Centro Internacional de Agricultura Tropical
(CIAT), AA6713, Cali, Colombia 2. Division of
International Health, Department of Public Health
Sciences, Karolinska Institute, SE-171 76,
Stockhplm, Sweden 3. The International Program
in the Chemical Sciences (IPICs), Uppsala
University Dag Hammarskolds vag 31, SE-752 37,
Uppsala, Sweden
It has been argued that the most effective
technology transfer approach to increase small
cassava farmer productivity and preserve his
environment must involves new crop varieties
(Kawano et. al. 1998). The CGIARs Impact
Assessment and Evaluation Group (IAEG) crop
germplasm study estimate that the annual
varietal productivity gains from CGIAR improved
crops ranged from 1-2 percent per year, with the
greatest impact on the twin evils of poverty and
environmental degradation (CGIAR1999). This
gain was made possible only by years of effort in
collecting, characterizing and systematically
using germplasm resources, especially local
traditional land races. For example, the highest
level of resistance To the cassava mosaic disease
found in some Nigerian land races surpasses
currently deployed resistance bbtained from a
wild relativefollowing more than 2 decades of
breeding (Fig1). The potential for continued
improvement in non-grain crop yields, especially
cassava, is indeed tremendous, given that useful
genetic diversity remains to be systematically
defined and exploited like has been done for
grain crops. For example heterosis or hybrid
vigor found in unrelated corn germplasm at the
turn of the century is be expected to occur in
cassava, considering that populations maybe
genetically differentiated and do have a high
frequency of partially or completely dominant
genes. Systematic efforts to study genetic
diversity are no doubt required in cassava
considering the vast phenotypic variation known
for the crop. Hundreds of thousands of land
races are held by farmers in Latin America and
Africa are indeed an invaluable resource for the
future but using them in a systematic way to
increase protect the cop and increase
productivity is a daunting task. New molecular
marker tools in cassava (Mba et. al. 2000) make a
study of genetic variation in cassava germplasm
a feasible goal in terms of time and resources.
These tools have been applied to the assessment
of genetic diversity of several collections made
in farmers fields and collections held
in International and national research
Institutes. Although the direct outputs of the
project are largely strategic, they will provide
IARC and NARS breeders with information on useful
genetic variability. The ultimate beneficiaries
of germplasm assessment and subsequent genetic
improvement are small, resource-poor,
subsistence farmers who typically produce
cassava. Farmers' benefits will generally start
to accrue 5-7 years later, after some breeding
efforts.
Summary of Workshop Report After 2 years of the
existence of the network, it a workshop was held
to review progresses, and discuss future
perspectives. The first MOLCAS workshop was held
August 22-24, 2000 at CIAT headquraters, Cali,
Colombia. It was attended by members of the
network from Swede,. Brazil, Malawi, Nigeria, a
representative from IPICs, the donor and
interested CIAT scientists, a total of 30
participants. Two days were spent reviewing the
results of cassava collections and analysis with
molecular markers in Brazil, Malawi, Tanzania,
CIAT, and IITA collections, the third day was
spent discussing future projects and deciding on
priorities. A total of 8 presentations were
made during the workshop. Three talks dwelled on
new methodologies, namely recent advances in
plant genomics and the implications for study and
use of genetic diversity GIS tools for guiding
collection of genetic diversity and the need to
involve farmers in the study of genetic
resources. There were 3 genetic diversity
assessment reports, conducted in Brazil, Malawi
and Tanzania respectively the other 2
presentations were from CIAT on the study of
genetic diversity in wild relatives and the CIAT
cassava collection. The presentation on
advances in plant genomics, given by Dr Matthew
Blair, CIAT bean geneticist, on behalf of Prof
Steve Kresovich, Director Genome diversity
Instititute of Cornelll University, was a good
introduction to advances and powerful new tools
of plant genomics that are redefining traditional
thinking on genetic diversity. In particular,
the new methods of uncovering bi-allelic, highly
abundant single nucleotide polymorphisms (SNPs)
promises to provide unprecedented resolution for
genetic studies. The studies of genetic
diversity assessment of cassava land races in two
African and one Latin American country provided
new evidence on the elucidation of the genetic
structure of cassava in its primary and a
secondary center of diversity. The studies,
conducted with SSR, AFLP, and RAPD markers
revealed a low level of genetic differentiation
in the land races along lines that are not fully
understood at the moment, although some evidence
points to bitter and sweetness of roots, and
multiple introductions. Questions raised about
the underlying reasons for observed organization
of genetic variation and the preservation of the
genetic structure in the primary and secondary
centers of will be the objective of further
studies. Finally, we were reminded about the
wisdom of properly marrying farmers knowledge of
cassava with molecular tools to make the best
interpretation of results.
The Network The molecular genetic diversity
network of cassava (MOLCAS) comprises of
scientists drawn from institutes in Malawi,
Uganda, Tanzania, Nigeria, Brazil, Sweden,
Colombia, France, and the USA, and it is funded
by the International Chemical Sciences Program
(IPICs), University of Uppsala. The goal of the
network is to enhance the enduring and emerging
roles of cassava as a food security crop and
industrial crop by the assessment and
exploitation of genetic variation. The network
assists members, with tools, information, and in
some instances funds, with the collection
molecular and agronomic characterization of
cassava land races in Africa and Latin America.
Studies concluded to date by members of the
network include ? SSR study of cassava land
races in Northern Malawi (Bvumbwe Agricultural
Research Station Malawi, SLU, Uppsala,
Sweden) ? SSR study of cassava land races in
Southern Tanzania (CIAT, SLU, ARI-Mwanza,
ARI-Mikocheni Tanzania) ? A molecular marker SSR
study of cassava land races from the Amazonian
basin and North Eastern coast of Brazil
(ICA-Campinas, Brazil) ? A comparative SSR study
of cassava land races from 7 Latin American and 2
African countries See Fig 2. Ongoing studies
include ? SSR study of a cassava collection
from the Amazonian region of Colombia (CIAT, Uni
Valle Colombia) ? SSR study of land races in
Nigeria (IITA, NRCRI Nigeria, CIAT) ? SSR study
of land races from the andean, forest and coastal
regions of Peru (in collaboration with
PRONIRGEB-INIA, Peru, IPGIR-CIAT office, CIAT) ?
SSR study of land races from Ghana (IITA, Crop
Research Institute (CRI), Accra Ghana, CIAT)
? Test for heterotic (hybrid vigor)
patterns in land races from central America and
Africa.
Fig 3. Hierarchical clustering (Ward) of Fixation
Index (FST) pair-wise distances between cassava
land races, grouped by country, and elite parents
by source.
Future Activities IPICs, the principal donor of
MOLCAS has invited the network to apply for
funding during the period 2001-2003, the last
session of the workshop was therefore spent
brainstorming projects the network considers
priority for the future. Anke Van de Hurk, IPGRI
scientist based at CIAT, served as a very able
facilitator in this process. In the period
2001-2003, the network has prioritized the
following studies ? SSR marker study of the
role seedlings play in preserving genetic
diversity during the disease epidemics
(Uganda) ? A study of broad adaptation of
cassava genotypes in Southern Africa (Malawi,
Tanzania, Mozambique, Uganda) ? Farmer
keys for identification of their varieties
(Malawi). ? A study of broad adaptation of
cassava genotypes in Brazil (Brazil) ?
Continuation of the country study of genetic
diversity structure (Democratic Republic of
Congo, Ghana and Mozambique) ? Development
of a set of highly polymorphic markers for
studying genetic diversity in cassava ? A
web-site to disseminate results and outputs of
MOLCAS activities ? Increase linkages to many
other groups interested in the molecular
diversity of cassava.
CGIAR. 1999. The CGIAR research agenda Facing
the poverty challenge. Mid-term meeting,
Washington D.C. USA, 22-28 October, 2000 CGIAR
Secretariat, World Bank, Washington D.C.. Kawano
K., Narintaranporn K., Narintaranporn P.,
Supachai S., Limsila A., Limsila J., Supahan D.,
Sarawat V., and Watananonta W. 1998. Yield
improvement in a multi-stage breeding program
for cassava. Crop Science 38325-332
Mba REC, Stephenson P, Edwards K, Mezer S,
Nkumbira J, Gulberg U, Apel K, Gale M, Tohme J,
Fregene MA (2000) Simple sequence repeat (SSR)
marker survey of the cassav (Manihot esculenta
Crantz) genome toward a SSR-based molecular
genetic map of cassava. Theor Appl Genet
10221-31
We thank the International Program in the
Chemical Sciences (IPICs), Uppsala University for
funding.