Progress and Challenges for the Deployment of Transgenic Technologies in Cassava

AgBioForum, 7(1&2): 51-56. ©2004 AgBioForum.
Progress and Challenges for the Deployment of Transgenic
Technologies in Cassava
Nigel Taylor, Lawrence Kent, and Claude
The production of genetically modified cassava (Manihot escu-
Fauquet
lenta Crantz) plants is routine in the advanced laboratories that
Donald Danforth Plant Science Center, St Louis
invested in this technology during the 1990s. The ultimate aim
of those engaged in cassava biotechnology is to develop and
deliver improved planting materials to farmers in the tropical
regions. Transgenic plants are now being produced that express
traits with potential agronomic importance. Although good sci-
ence will remain an essential basis for this goal, if farmers are to
benefit from this investment, it is essential that researchers and
others involved in these programs adopt a mindset geared
towards product development and delivery. The first field trials
of cassava are now under way. This paper examines the major
challenges facing public sector research organizations engaged
in the transgenic improvement of cassava.
Key words: cassava, field trial, intellectual property, product
development, transgenic.
Introduction
Production of enhanced germplasm through conven-
It is possibly among the vegetatively propagated
tional breeding is problematic in the vegetatively propa-
“orphan crops” that transgenic technologies can have
gated crops. Cassava, in common with the other species
the biggest impact. Despite their importance as sources
listed above, is characterized by strong heterozygosity
of both food and income for billions of people in the
and inbreeding depression. Breeding programs in cas-
tropical and subtropical regions, yields in these crops,
sava consist of crossing elite parents and screening
which include cassava (Manihot esculenta), plantains
thousands of first-generation progeny for desired char-
(Musa spp), sweetpotato (Ipomea batatas), taro (Colo-
acteristics (Ceballos, Iglesias, Perez, & Dixon, in press).
casia esculenta), and yams (Dioscorea spp), have
Although important contributions to disease resistance
increased by less than 30% over the last 40 years. This
and harvest index have been achieved in this manner
contrasts with rice and wheat, which benefited greatly
(Jennings & Iglesias, 2002; Kawano, 2003), many
from investment during the Green Revolution and real-
believe that transgenic technologies offer the key to
ized yield improvements of at least 80% and 100%
unlocking the full potential of cassava. Insertion of
respectively over the same period (Food and Agriculture
genetic material by direct gene transfer allows benefi-
Organization of the United Nations, 2004). The vegeta-
cial traits to be integrated rapidly into elite germplasm
tively propagated food crops therefore have a largely
without changing the genetic background of the mother
untapped potential for improvement in both quantity of
plant. In this way, desired traits can be introgressed into
production per unit area and for development as com-
elite parent material prior to sexual crossing or into the
modity products within developing economies. How can
products of a breeding program that lack a specific trait
this potential be exploited, and how can the resulting
required by farmers. In other cases, existing farmer-pre-
benefits be passed to farmers and consumers in develop-
ferred landraces and varieties can be modified to per-
ing countries? In this article, we will use the root crop
form better in a given environment. An example of the
cassava as an example of the progress being made and
latter approach is the introduction of transgenic resis-
the challenges faced in attempting to bring the potential
tance against cassava mosaic viruses into susceptible
of biotechnology to bear on vegetatively propagated
landraces grown by small farmers in Africa or into culti-
crops. Great promises made by proponents of agricul-
vars grown for commercial-scale starch production in
tural biotechnology—from both the private and public
southern India. Biotechnology also allows the introgres-
sectors—cite such potential as justification for contin-
sion of beneficial traits not accessible through conven-
ued investment into research and development in this
tional means, such as herbicide tolerance and Bt-
field. It is hoped that this article will illustrate some of
imparted resistance against stem borers and hornworms
the realities involved in attempting to deliver on this
(Taylor, Chavarriaga, Raemakers, Siritunga, & Zhang,
rhetoric.
in press).

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AgBioForum, 7(1&2), 2004 | 52
Present Status of Transgenic Cassava
cases, technologies successfully developed in other
The potential of transgenic technologies for improving
crops have been transferred to Manihot esculenta.
cassava was first recognized in the late 1980s. At that
Transgenic cassava plants produced to date represent
time, a small group of scientists established the Cassava
proof of concept for the respective traits in this species,
Biotechnology Network (CBN; Thro et al., 1999), to act
with efficacy of the transgenic strategy demonstrated at
as a mechanism to bring together researchers in devel-
the laboratory and/or greenhouse level. For a more
oping and industrialized countries with a shared vision
extensive review of the technologies used to generate
for using advanced molecular tools to improve the crop.
these plants, the reader is referred to a recent review
It was not until 1996, however, that recovery of the first
compiled in collaboration by the five laboratories with
transgenic cassava plants was reported (Li, Sautter, Pot-
existing capacity to produce transgenic cassava (Taylor
rykus, & Pounti-Kaerlas, 1996; Raemakers et al., 1996;
et al., in press).
Schopke et al., 1996). This frustrating delay arose from
The ultimate aim of transgenic programs in cassava
an inability to generate the totipotent tissues required to
is to develop and deliver improved planting materials to
produce transgenic plants. An interesting comparison
farmers in the tropical regions. Publication of technical
can be made between rice and cassava, both of which
achievements in scientific journals cannot, therefore,
were considered recalcitrant to in vitro manipulation in
represent the end point of such endeavors, but are mile-
the mid-1980s. Within ten years, mostly as a result of
stones in a product development and delivery process.
initiatives by the Rockefeller Foundation, transgenic
As a first step in this direction, investment is being made
technologies for japonica rice became so routine that
to test existing transgenic plant lines under field condi-
they were considered model systems for plant genetic
tions. Transgenic cassava plants have been field trialed
transformation. Progress in cassava was distinctly
in the US Virgin Islands and within screenhouse facili-
slower, due to much lower levels of investment in the
ties in Western Kenya, and confined trials are in prepa-
biotechnologies required for the improvement of the
ration at CIAT in Colombia.
crop. With fewer than seven laboratories engaged in
transgenic technologies for cassava worldwide, generat-
Challenges to Deployment of Transgenic
ing a critical mass of researchers proved to be difficult.
Cassava
The CBN, through its international meetings and small
As the initial technical hurdles have been overcome,
grant systems, was instrumental in encouraging collabo-
new challenges are becoming apparent. Although not
ration between research groups in the United States,
specific to cassava, these represent major hurdles that
United Kingdom, The Netherlands, Switzerland, and the
must be overcome if the technology is to move forward
CGIAR center at Centro Internacional de Agricultura
from proof of concept to product development, deregu-
Tropical (CIAT) in Colombia. Breakthroughs in the abil-
lation, and commercial release. The challenges being
ity to generate morphogenic culture systems (Li et al.,
faced by the small group of researchers engaged in this
1996; Taylor et al., 1996) eventually resulted in the pro-
effort are varied and include further technical questions,
duction of cassava plants transgenic for marker genes
intellectual property rights, the underdeveloped regula-
both via microparticle bombardment (Raemakers et al.,
tory environment and biosafety infrastructures within
1996; Schopke et al., 1996) and Agrobacterium-medi-
target countries, and of course accessing the funding
ated gene integration (Li et al., 1996).
needed to solve these issues. The inexperience of most
Since the first reports of transgenic plant recovery in
public-sector research scientists in handling a product-
cassava, efforts have focused on integrating genes with
delivery process, and the need to achieve these goals
the potential to impart traits of agronomic interest.
within the tropical regions, are also important factors
Genetically transformed plants have been recovered
that must be overcome in the technology transfer pro-
with reduced cyanogenic content (Siritunga & Sayre,
cess.
2003), resistance to infection by geminiviruses (Chel-
lappan, Masona, Ramachandran, Taylor, & Fauquet, in
Technical Issues
press), expression of Bt proteins (Ladino et al., 2002),
Desired traits within a transgenic plant must be
modified starch content (Raemakers et al., 2003;
expressed at the required level and in a predicable man-
Uzoma, Arias-Garzon, & Sayre, 2003), and elevated
ner under conditions that the crop experiences during
protein content within the storage roots (Zhang, Jaynes,
cultivation. Presently, little data is available regarding
Potrykus, Gruissem, & Pounti-Kaerlas, 2003). In most
how transgene expression will be affected when geneti-
Taylor, Kent, & Fauquet — Progress and Challenges for the Deployment of Transgenic Technologies in Cassava

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AgBioForum, 7(1&2), 2004 | 53
cally modified cassava plants are cultivated in the field
relatively straightforward. In such cases, a few cultivars
in the tropics. As with other vegetatively propagated
may be grown over tens of thousands of hectares in a
crops, obtaining homozygous transgenics in cassava is
situation not unlike maize in the United States. Africa,
not practical, meaning that required levels of expression
the world’s largest cassava-producing region, presents a
must be obtained and reliably sustained at the T0 gener-
different scenario, where cassava remains very much a
ation over many vegetative cycles. Such goals have
small-farmer crop grown in mixed stands as a source of
been achieved for Solanum potato (Kaniewski & Tho-
food for the family. As a result, scores of landraces and
mas, 2004, this issue), but empirical studies on stability
varieties may be grown in any given region, and deci-
of transgene expression in cassava must be confirmed
sions regarding which landraces, varieties, and breeding
by carrying out field trials for specific traits in this crop.
lines to target for investment through transgenic
The challenges involved in establishing the required tri-
improvement must be made with care and with signifi-
als in the tropics are not trivial and are discussed below.
cant input of local knowledge.
As with all crop species, significant variability exists
There are also technical challenges in culturing the
in the response of different cassava cultivars to the
prioritized germplasm and adjusting the transformation
available genetic transformation protocols. To date,
systems to allow efficient production of transgenic
most transgenic cassava plants ready for field trial are of
plants. The capacity to generate the 15–30 independent
model cultivars that have proved to be amenable to the
transgenic events required at the proof-of-concept stage
genetic transformation protocols. In seed-propagated
must be increased tenfold (or more) in order to reliably
crops, it is possible to integrate a desired transgenic trait
generate plants of the quality required for release to
into one or a few easily transformable cultivars and then
farmers. Most public-sector research facilities are not
backcross these with local varieties to generate the
experienced in, or geared up for, this level of output. To
desired products. In most cases, this is not an option for
date, data is available for transgenic plant production in
the vegetatively-propagated crops, because the aim is to
six cultivars of cassava. With the appropriate investment
enhance existing farmer-preferred germplasm or elite
many more could be brought into the existing systems.
breeding lines without altering their existing desirable
For example, production of embryogenic tissues—the
characteristics. As transgenic cassava programs move
central component of transgenic protocols in cassava—
towards a product development mode, it is essential that
has been reported in more than 60 varieties (Taylor et
capacity to produce genetically transformed plants is
al., in press), so there can be optimism that farmer-pre-
expanded into the agronomically most important variet-
ferred varieties from all the tropical regions can be
ies and breeding lines within the major cassava-growing
genetically transformed with the appropriate invest-
regions.
ment. However, adapting the tissue culture systems to
Transgenic programs are multiyear, multimillion-
suit priority germplasm requires time and resources that
dollar efforts and must generate products readily accept-
the leading laboratories based in North America,
able to the intended end users. Failure to genetically
Europe, and the CGIAR Centers would rather invest in
modify the relevant germplasm will result in a signifi-
trait development and transgene expression studies. It is
cant waste of resources, regardless of the effectiveness
considered important, therefore, that in the near future,
of the transgenic trait. To prevent this, one must identify
development of the culture systems required for trans-
which cassava varieties and landraces are dominant
formation of specific cassava varieties be carried out
within a given region, what traits they are lacking, and
within the respective cassava-growing regions. To this
what role they play within the local cropping system.
end, training of scientists and technicians from the
For example, investing in the genetic enhancement of a
national agricultural research systems (NARS) within
cultivar primarily grown for sale to the local starch-pro-
the tropical regions must be a priority within transgenic
cessing factory may have a more significant impact on
cassava programs (Taylor, Schöpke, Masona, & Fau-
the well-being of farmers than the same enhancement
quet, 1999).
applied to a variety primarily cultivated for on-farm
consumption. It can be appreciated that this knowledge
Intellectual Property
is not part of the average biotechnologist’s repertoire but
Some claim intellectual property (IP) issues to be a
requires the skills and input of agricultural economists.
major factor limiting the deployment of transgenic tech-
In some situations, such as in Asia, India, and parts of
nologies in developing countries, while others consider
Latin America, where cassava is increasingly grown on
this to be a trivial problem if the correct procedures are
a commercial scale, identification of priority cultivars is
Taylor, Kent, & Fauquet — Progress and Challenges for the Deployment of Transgenic Technologies in Cassava

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AgBioForum, 7(1&2), 2004 | 54
followed early in the product delivery program. The lat-
the optimal insertion events. Although field trials of
ter tend to be those knowledgeable in IP issues and with
transgenic crop plants are common in North America
access to legal advice on such matters. The experience
(more than ten thousand have been safely carried out in
of the authors and other cassava biotechnologists falls
the United States since 1989), equivalent levels of expe-
somewhere between these views, but it is certain that IP
rience do not exist in the countries where tropical crops
presents a potential minefield which must be negotiated
such as cassava are central components of the staple
carefully. Ensuring compliance with IP consumes scarce
diet. Although many developing countries have assem-
resources and in some cases has prevented the develop-
bled the regulatory structures required to carry out field
ment of potentially beneficial products in cassava.
trials, the existing legislation is often outdated, and the
Of the five laboratories engaged in production of
process itself has never been put into practice. The result
transgenic cassava, two are partially funded by commer-
is that the human skills and biosafety infrastructure
cial starch companies interested in the use of biotech-
required to carry out field trials are lacking. This is most
nology to modify the starch content of cassava storage
especially the case in sub-Saharan Africa, where to date
roots. In these cases, the commercial backers have the
outside of South Africa, only Kenya, Zimbabwe, and
experience and resources available to ensure that all IP
Burkina Faso have carried out field trials of transgenic
issues are resolved prior to commencing product devel-
plants, with the combined number in all three countries
opment. Within the public sector, naivety in the impor-
totaling fewer than ten.
tance of such issues can lead to problems, although this
This situation obviously presents significant obsta-
is a situation that is improving as researchers gain hard-
cles for those wishing to develop a product delivery pro-
won experience in this area. Recent sublicensing of
cess within such regions. For example, an application to
enabling technologies from Monsanto Company to the
field trial cassava in Nigeria presently requires detailed
Donald Danforth Plant Science Center (see Horsch &
answers to 150 separate questions. When this applica-
Montgomery, 2004, this issue) for use by the cassava
tion was completed by the Donald Danforth Plant Sci-
community provides an example of an increasing range
ence Center (DDPSC) in collaboration with its partners
of proprietary tools becoming available to those
in that country, it reached almost 60 pages in length.
engaged in these efforts.
Establishing a screenhouse trial of cassava in East
Acquiring freedom to operate with transgenes
Africa required the DDPSC to commit approximately
imparting valuable traits can also be problematic. When
$150,000 worth of resources, over a period of a year, to
the intended aim is field deployment, lengthy and some-
cover training of African staff, upgrading containment
times costly negotiations must be initiated with the own-
infrastructure, processing the application through the
ers of such technologies. In some cases—for example,
biosafety committees, and numerous exchange visits
the EPSP-synthase (epsps) gene, which imparts resis-
between Africa and the United States. Such levels of
tance to the herbicide glyphosate—significant efforts
investment are a very significant undertaking for public
driven by farmer-identified needs in Colombia have
research organizations. Decisions about whether to
failed to gain access for use of this gene in cassava. This
spend scarce resources on such endeavors have to be
is certainly disappointing for those involved, most espe-
balanced against other demands, such as the need to
cially as a subsequent ex ante study of the potential
publish in high quality peer-reviewed journals and
impact of glyphosate-resistant cassava indicates that this
thereby secure future funding for the research. It is
technology could be worth as much as $300 million to
hoped that programs such as Plant Biosafety Systems
the Colombian economy over a 15-year period (Pachico
(PBS, funded by the United States Agency of Interna-
& Rivas, 2003).
tional Development) will be successful in their efforts to
modernize the regulatory environment in developing
Regulatory Challenges for Establishing Field
countries, and that as a record of safe field trials is estab-
Trials
lished, the process will become progressively simplified
Genetically modified crop plants must be tested in the
and routine. Indeed, it is essential that this is achieved if
environments where they will be cultivated by farmers.
transgenic crops are to be developed and released to
Multiple trails in different locations within a target
farmers in these regions.
country are required for determining efficacy of the
transgenic trait, eliminating off-types generated during
the tissue culture/transformation process, and selecting
Taylor, Kent, & Fauquet — Progress and Challenges for the Deployment of Transgenic Technologies in Cassava

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AgBioForum, 7(1&2), 2004 | 55
Funding for Transgenic Modification of
addressed and solved if the benefits of biotechnology
Cassava
are to reach end users in developing countries. The text
Sustaining required levels of funding remains a major
above is not intended to convey pessimism, but to high-
concern for all research organizations engaged in
light the amount and type of work that needs to be done.
genetic modification of cassava. Despite the importance
Not all issues have been covered. For example, ques-
of the crop—after rice and maize, cassava is the most
tions of how new transgenic crops such as cassava will
important source of dietary calories in the tropics and is
be tested for food and environmental safety and deregu-
cultivated on a total area only 7% less than that commit-
lated for commercial release in the tropics, and who will
ted to potato—resources available for the improvement
pay for this process, have not been discussed. Instead,
of cassava are severely restricted. Cassava and the other
we have focused on the more immediate requirements
orphan crops listed above are not cultivated in the indus-
as experienced by those involved in such research and
trialized nations and are therefore not mandated for the
development programs. These include the need to test
large investments spent in improving species such as
prototype technologies in the field and to adapt trans-
maize and wheat. Indeed, cassava is most important in
genic capacity to include the most important farmer-pre-
the world’s least developed countries, where govern-
ferred planting material. Although good science remains
ment support for agricultural research is insufficient and
an essential base, on its own it will not deliver benefits
often nonexistent for development of the relevant bio-
to people in developing countries. Genuine commitment
technologies. A review of the Agricola database illus-
is required from research organizations and funding
trates this discrepancy in biotechnology investment.
bodies to tackle the less glamorous tasks of improving
Agricola shows citations for 471 and 242 papers
regulatory infrastructure in developing countries and
describing transgenic systems in maize and wheat
training scientists and regulators from these countries. If
respectively, but only 36 for cassava and two for plan-
sustainable programs for transgenic improvement of
tain.
tropical crops are to be achieved, it is also most impor-
Most funding for transgenic improvement of the
tant that capacity for development and deployment of
orphan crops is provided by aid agencies and charitable
genetically modified crops in developing countries is
foundations. Although commendable, this support is
acquired by its own people and that they are actively
most often piecemeal, and from the perspective of the
engaged in driving all levels of the process—from prior-
researchers, unpredictable. As a result, at any given
ity setting to production and analysis of transgenic
time, none of the laboratories engaged in transgenic cas-
plants, field testing, and commercial deregulation.
sava programs have guaranteed support for more than
one to three years into the future. Building and main-
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Document Outline

• Introduction
• Present Status of Transgenic Cassava
• Challenges to Deployment of Transgenic Cassava
  • Technical Issues
  • Intellectual Property
  • Regulatory Challenges for Establishing Field Trials
  • Funding for Transgenic Modification of Cassava
• Conclusions
• References

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