GM technology series
Achieving successful deployment
of Bt rice
Sasha Ming High1
, Michael B. Cohen2
, Qing Yao Shu3,4
and Illimar Altosaar1
1
Department of Biochemistry, Microbiology and Immunology, Faculty of Medicine, University of Ottawa, 451 Smyth Road, Ottawa,
ON, Canada K1H 8M5
2
Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E9
3
Institute of Nuclear Agricultural Sciences, Zhejiang University, Hangzhou 310029, China
4
Present address: Plant Breeding and Genetics Section, Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture,
International Atomic Energy Agency, Wagramer Strasse 5, A-1400, PO Box 100, Vienna, Austria
An additional billion mouths will need feeding within
the next decade. In spite of the extensive research and
development that has been invested in Bt rice (rice
transformed with insecticidal genes from Bacillus thuringiensis)
and the success of Bt maize and Bt cotton, Bt
rice is not grown commercially. Bt rice has the potential
to eliminate yield losses caused by lepidopteran pests,
estimated at 2–10% of Asia’s annual rice yield of 523
million tons. Cultivation of Bt rice should also lead to
substantial reductions in the use of broad-spectrum
chemical insecticides, with benefits for farmers’ health,
environmental quality and biological control of other
rice pests. The major challenges are developing appropriate
resistance management strategies and resolving
trade policy impediments.
The global population is steadily growing while the
amount of arable land is steadily decreasing. Thus, it is
essential that sustainable strategies be implemented to
use agricultural resources efficiently to yield an abundant
healthy diet. Experience to date with genetically engineered
crops has shown that this technology can make
substantial contributions towards this goal. Among the
first transgenic crops approved for release were Bt maize
and Bt cotton, which contain genes encoding insecticidal
proteins from the bacterium Bacillus thuringiensis. These
crops have been readily adopted by farmers, have resulted
in increased yields and reductions in insecticide applications,
and have been sustainable when used with
resistance management programmes [1]. However, continuing
controversies surrounding the risks and benefits of
this novel technology have prevented its benefits from
reaching consumers in many parts of the world.
Rice is the target crop for many improvement programmes
because it is the staple diet for nearly two billion
people worldwide and the major food for over half of those
living in Asia [2]. At the 2003 International Congress of
Plant Pathology (Christchurch, New Zealand), Zhangliang
Chen (President of the China Agricultural University)
announced that China was feeding 22% of the world’s
population using only 7% of the available land* and that
their productivity is currently dependent on heavy
chemical inputs. In 2002, rice production in China reached
177 million tons, of which 3.1 million tons was exported,
producing revenue of US$578 million (http://www.irri.org/
science/ricestat/index.asp). These numbers represent only
a fraction of what might be available if rice plants were not
subject to insect attack. Many rice varieties have been
transformed with genes encoding various Bt crystal (Cry)
proteins and have been shown to be resistant to one or
more lepidopteran pests of rice (Table 1), the most
important of which are the yellow stem borer (Scirpophaga
incertulas), the striped stem borer (Chilo suppressalis) and
several species of leaf-folders (Marasmia spp. and Cnaphalocrocis
medinalis) [3]. Field trials of Bt rice commenced
in China in 1998 [4–6] and in India in 2001 (S.K.
Raina, pers. commun.) (Table 2), but no Bt rice or other
transgenic rice varieties have yet been released for
commercialization. Here, we review the potential benefits
of Bt rice, biosafety issues, approaches to resistance
management and the regulatory issues that continue to
delay the release of this technology to farmers.
Benefits of Bt rice
The use of Bt cotton has resulted in substantial decreases
in insecticide use in developed and developing countries,
and, in some cases, also in increases in yield and profitability
[1,7]. For example, farmers growing Bt cotton in
India gained a 70% reduction in insecticide applied, a
saving of US$30 per hectare in insecticide costs and a
revolutionary yield increase of 80–87% [7]. In a survey
conducted in China in 1999, the average number of
pesticide applications by farmers using Bt cotton was 6.6
per crop, compared with 19.8 for farmers growing
conventional cotton, and the proportion of farmers reporting
pesticide poisoning symptoms was 4.7% compared
with 22% [8]. Hopefully, anticipated downstream public
health improvements will continue to be monitored in
Bt-cotton-growing areas, documenting the longer-term
Corresponding author: Illimar Altosaar (altosaar@uottawa.ca).
* Chen, Z. (2003) Feeding a quarter of humanity: challenges and the role of modern
technology. Abstracts of offered papers, 8th International Congress of Plant Pathology,
Christchurch, New Zealand, 2–7 February 2003.
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www.sciencedirect.com 1360-1385/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.tplants.2004.04.002
benefits of reductions in the use of broad-spectrum
insecticides.
Decreases in insecticide use and increases in yield and
profitability resulting from Bt rice, although still substantial,
will be less dramatic than those for Bt cotton. Rice
stem borers and leaf-folders cause less yield loss than do
lepidopteran pests of cotton and are the targets of fewer
insecticide applications. It is challenging to quantify yield
losses in rice because of the large and variable area over
which the crop is grown. In the most rigorous study to date,
Serge Savary et al. [9] found that total yield losses caused
by weeds, diseases and insects ranged from 24% to 41%
depending on location and production situation. Among
insect pests, stem borers (the principal target of Bt rice)
caused the greatest yield loss, estimated at 2.3% [9].
Typically, yield losses caused by stem borers have been
estimated at 5–10% [3]. In China, losses caused by rice
stem borers, in spite of the use of insecticides, were
estimated as 3.1% of the national rice yield, equivalent to a
monetary loss of 6.45 billion renminbi (RMB) (US$780
million) [10]. The cost of chemical control of stem borers
was estimated as RMB2.85 billion, with ecological and
health costs of RMB1.45 billion to RMB2.85 billion and
RMB0.3 billion, respectively [10]. Total pesticide costs
account for less than 3% of the production costs of
Asian rice farmers but the number of applications
varies greatly [11]. For example, farmers in Zhejiang
Province (China) (Figure 1) apply 20 times as much active
ingredient as those in Central Luzon (The Philippines).
The relatively small proportion of production costs
attributable to pesticides is in part a result of the relatively
low cost of pesticides and of a decline in insecticide use in
some countries where integrated pest management (IPM)
training programmes have been implemented. In IPM
courses, farmers learn that most insecticide applications
are unnecessary because yield losses are generally overestimated
and that insecticides disrupt biological control
of pests by predators and parasitoids [12]. Early-season
sprays directed at leaf-folders have been particularly
targeted by insecticide reduction programmes because rice
plants can readily compensate for defoliation that occurs
at the vegetative stage [13].
In relation to the size of Asia’s rice harvest of 523 million
tons (http://www.irri.org/science/ricestat/index.asp), the
estimated 2–10% yield loss attributable to stem borers
and leaf-folders across the region represents an enormous
amount of rice. In addition, insecticide reductions that will
result from the introduction of Bt rice will confer
Table 1. Bt rice lines with resistance to lepidopteran pestsa
Cultivar Promoter Gene Refs
KMD1b
, KMD2b
Ubiquitin cry1Ab [4,57]
Elite Eyi 105, Bengal Ubiquitin cry1Ac [58]
IR64, Pusa Basmati-1, Karnal Local Ubiquitin cry1Ac [59]
Basmati 370 Ubiquitin cry1Ab, cry1Ac [60]
IR58 CaMV 35S cry1Ab [61]
IR72, IR-64, CBII, Taipei-309, IR68899B, MH-63–63,
IR51500-AC11, Vaideh-1, IRRI-npt
CaMV 35S, Actin-l, pith tissue-specific, PEPC cry1Ab [62]
Tarom Molaii PEPC cry1Ab [63]
IR64 Ubiquitin cry1Ac [64]
Vaidehi, TCA-48 CaMV 35S cry1Ab [65]
Basmati-370, M-7 CaMV 35S cry2A [66]
Kaybonnet, Nipponbare, Zhong8215, 93VA, ZAU16, 91RM,
T8340, Pin92-528, T90502
Ubiquitin cry1Ab, cry 1Ac [67]
Taipei-309 CaMV 35S cry1Ab [68]
Basmati 370 Pollen-specific, ubiquitin, PEPC cry1Ab [69]
Ariete, Senia Ubiquitin cry1B [70]
Ariete Maize proteinase inhibitor cry1B [71]
CMS restorer Minghui 63b
, Shanyou 63b
Actin-1 cry1Ab/cry1Ac hybrid gene [5]
Abbreviations: CaMV, cauliflower mosaic virus; PEPC, phosphoenolpyruvate carboxylase.
a
Data modified from Ref. [72].
b
Lines have been field tested in China.
Table 2. Milestones in the development of Bt rice
1981 First cry gene cloned and sequenced [73]
1984–1999 Inception of The Rockefeller Foundation’s International Rice Biotechnology Program
1985 Transformation of plants with cry genes [74–77]
1986 First field tests of plants transformed with cry genes in the USA and France
1988 First field trials of Bt cotton in the USA [78]
1993 First published report of japonica rice transformed with cry gene [79]
1994 Opening of containment greenhouse at International Rice Research Institute, The Philippines, for
growth of transgenic plants
1995 First published report of indica rice transformed with cry gene [61]
1996 First growing season by farmers of Bt maize, Bt cotton and Bt potato
1997 First growing season by farmers of Bt cotton in China [8]
1997 Field trials of Bt cotton begin in India [7]
1998–1999 Field tests of Bt rice begin in China [4–6]
1999 First published report of rice transformed with two cry genes [55]
2001 Field tests of Bt rice begin in India S.K. Raina, pers. commun.
2002 First growing season by farmers of Bt cotton in India [7]
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important benefits to environmental quality and the
health of farmers and consumers. Particularly, extensive
pesticide run off from rice fields pollutes not only ground
water but also environments far away from rice paddies.
Furthermore, because many pesticides are not degraded
before the rice is eaten, they pose potential risks for rice
consumers. For these reasons, the benefits of Bt rice might
be far greater than the benefits of Bt cotton. Rice currently
imported into Canada, for example, can contain the
following pesticide levels: 25.0 ppm HCN, 5.0 ppm quinclorac,
2.0 ppm methoxychlor, 0.5 ppm Naled, 0.05 ppm
bentazon, 0.1 ppm other pesticides (http://www.hc-sc.gc.
ca/food-aliment/friia-raaii/food_drugs-aliments_drogues/
act-loi/pdf/e_c-tables.pdf). A global goal should be to
engender regulations that would see these contaminants
removed from the rice supply and replaced by Cry proteins
as expeditiously as possible.
With respect to transgenic crops in general, much is
made of hypothetical unintended effects – not all of these
are necessarily negative. A valuable unintended benefit
observed in Bt maize is a reduction in levels of mycotoxins
[14], some of which are known carcinogens. In maize, the
single determinant of mycotoxin in the grain is grain
damage, which is caused almost exclusively by insect
feeding. Rice grains can be contaminated with mycotoxinproducing
fungi during growth [15]. It is possible that stem
borer larvae that feed on developing panicles increase
mycotoxin contamination. Bt rice might also reduce the
spread and propagation of fungi in storage if the grains are
resistant to feeding by lepidopteran pests of stored grain,
such as the Angoumois grain moth (Sitotroga cerealella) or
the rice moth (Corcyra cephalonica).
Biosafety concerns
Outcrossing
Asia was the origin of the genus Oryza. Two common wild
rice species in Asia, Oryza nivara and Oryza rufipogon,
have the same AA genome as cultivated rice, Oryza sativa,
and are known to hybridize with cultivars under field
conditions [16,17]. In addition, there are many weedy rice
types in Asia derived from O. rufipogon, O. nivara,
O. sativa or hybrids of cultivars and wild rice [18]. Not
all rice crops flower synchronously with neighbouring wild
rice populations and, when they do, the outcrossing rate is
generally low. For example, one study in Hunan Province
(China) [19] found a maximum of 3% outcrossing to
O. rufipogon. Cultivated rice is primarily self-pollinated
and outcrossing among cultivars occurs at a low rate. The
outcrossing rate between transgenic and non-transgenic
cultivars in a field test in Spain ranged from 0.05 to 0.53%
[20]. Nonetheless, given the vast area over which rice is
cultivated and wild and weedy rices occur, transgenes will
almost certainly escape into non-transgenic plants. Novel
technologies under development that can restrict pollen
fertilization and seed germination might reduce the rate of
outcrossing when transgenic pollen does happen to
encounter non-transgenic flowers [21]. The extent to
which transgenes will persist and spread in wild and
weedy rices and in non-transgenic cultivars and the
possible consequences of outcrossing will need to be
assessed on a case-by-case basis.
Dozens of improved rice cultivars containing single
major genes conferring resistance to insects such as the
brown planthopper and rice gall midge or to diseases such
as rice blast or rice tungro virus have been widely grown in
Asia since the 1970s [2]. Traditional rice cultivars and wild
rice species have served as the sources of these resistance
genes, which have been transferred to modern cultivars by
conventional breeding. There are no known cases in which
wild or weedy rice populations have become more
aggressive as a result of outcrossing of resistance genes
from cultivars, although we are not aware of any studies
that have examined this question. Pre-release studies on
the impact of transgene outcrossing might be appropriate
in some areas for transgenes that confer traits that are not
found in traditional cultivars or wild rice species, such as
high levels of resistance to stem borers (as conferred by
Bt cry genes) or to abiotic stresses such as drought or
salinity. Many rice-growing areas of Asia, such as central
China, do not harbour populations of O. rufipogon or
O. nivara, whereas in others, such as the Mekong Delta of
Vietnam, one or both of these species are abundant [22].
Surveys in the Mekong Delta indicate that stem borer and
leaf-folder populations on O. rufipogon and weedy rices are
generally low, suggesting that outcrossing of Bt genes to
these plants will not strongly affect their distribution or
abundance (M.B. Cohen et al., unpublished).
Impact on biodiversity
An outstanding feature of Bt crops is that cry toxins have
little or no effect on non-target organisms [23]. The
introduction of conventional insecticides to Asian rice
production in the 1970s had a devastating impact on
arthropod predators and parasitoids of rice pests, resulting
in vast outbreaks of the brown planthopper (Nilaparvata
lugens) [12]. Insecticides also drastically reduced the
populations of fish and crabs in rice fields, which are
harvested for food. By contrast, results from laboratory
and field studies with Bt maize, Bt cotton and Bt potato
Figure 1. Intensive rice production over the past 40 years has seen the widespread
use of pesticides by farmers, particularly insecticides, perhaps one of the most
damaging environmental consequences. Insecticide use has exploded because of
both supply and demand factors [11]. Photograph courtesy of Gongyin Ye.
Review TRENDS in Plant Science Vol.9 No.6 June 2004288
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indicate that these crops are generally not toxic to
beneficial arthropods and non-target organisms [24].
Laboratory and field studies to date with Bt rice provide
a similarly positive picture, although monitoring in larger
field plots will be essential when cultivation of Bt rice on a
larger scale is permitted. In small-scale field trials in
China, population densities of five common spiders were
similar in plots of Bt and non-Bt rice [25]. Brown
planthoppers reared on Bt rice were found to ingest Bt
toxins but were not toxic when fed to the most important
predator of planthoppers, Cyrtorhinus lividipennis [26]. In
a field experiment in The Philippines, Bt sprays were used
to simulate a major effect of Bt rice, the removal of foliagefeeding
caterpillars, and to quantify the impact on the
arthropod community [27]. No disruptions in the biological
control of non-target herbivores were found. It is likely
that the introduction of Bt rice will enhance biological
control in rice fields if farmers reduce insecticide applications
directed against lepidopteran pests. Gongyin Ye
et al. [6] noted that, although no planthopper outbreaks
occurred in their plots of Bt rice (which received no
insecticide applications), outbreaks did occur in nearby
insecticide-sprayed fields of non-Bt rice.
Food safety
More than 100 years of science supports the use of
B. thuringiensis as a biological pesticide system [28].
The US Environmental Protection Agency has found no
evidence that Bt crops currently registered are toxic or
allergenic to humans [23]. Studies have reported an
absence of acute, subchronic and chronic oral toxicity to
mammals associated with Bt microbial pesticides, which
also contain Cry proteins [29,30]. Investigations of the
digestive fate of recombinant DNA and proteins have
found that the amount of intact transgenic DNA and
proteins in the digestive tract is minimal to zero [31].
Chickens fed YieldGardw Corn Borer maize event MON
810 (Monsanto, http://www.monsanto.com) were analysed
and none of the extracted chicken breast muscle samples
contained any detectable transgenic DNA or Cry1Ab
protein [32]. In another study, pigs fed transgenic Bt
maize were slaughtered, and no recombinant or maizespecific
DNA was detectable in the tissue samples [33]. A
study of cows fed Bt maize found only short DNA
fragments (,200 bp) present in the blood lymphocytes;
in all other organs, plant DNAs were not detected [34].
Three recent studies have examined the food safety of
Bt rice. Bt rice flour containing the cry1Ab gene was fed to
test rats in a 90-day feeding trial and no toxic effects were
found at dosages of up to 64 g per kg body weight [35].
Parental and Bt rice were compared for their major
nutritional components and physicochemical properties.
There were no significant differences in major nutritional
components (crude protein, crude lipid, free amino acids,
total ash and mineral elements) between the primary
transgenic rice KMD and the wild-type Xiushui 11, or
between the recurrent parent Jiazao 935 and new
transgenic line Huachi B6, which was bred using KMD
as the insect-resistant donor. Although a small amount of
Cry1Ab protein was detected in raw rice, no transgenic
protein was detected in the cooked rice [36]. In much more
extensive feeding trials currently under way with Bt rice
and rice expressing a plant haemagglutinin known to be
toxic to mammals, animals fed the Bt rice variety KMD1
presented microindicators that were essentially identical
to those observed in animals fed the nontransgenic
parental variety Xiushui 11 rice (Q.Y. Shu et al.,
unpublished).
Resistance management
Insect adaptation to conventional insecticides and crop
cultivars has been a pervasive and costly problem in pest
management [37]. As yet, there have been no measurable
increases in the frequency of resistance in pest populations
exposed to Bt crops in the field, but many insect species
have been shown to evolve resistance to Cry proteins
under laboratory conditions. The absence of pest resistance
to Bt crops is probably due in part to the
implementation of resistance management strategies in
countries where the crops have been released on a large
scale and in part to other factors such as fitness costs of
alleles conferring resistance [38]. In the USA and
Australia, farmers who grow Bt crops are required to
maintain refuges (fields or rows of non-Bt cultivars)
corresponding to 5–50% of the area planted with Bt
cultivars. Refuges maintain sufficient numbers of wildtype
susceptible insects in the population, reducing the
likelihood that insects carrying mutations for resistance
will mate with each other and produce homozygous
resistant progeny. Bt cotton farmers in China are not
required to plant refuges. Instead, it has been argued that
alternative host plants of the principal pest, Heliothis
armigera, serve as refuges [39]. In most cases (Bt maize
with resistance to rootworms being the exception), the
USA also requires that Bt cultivars contain a high dose of
toxin. This is defined as a dose that results in functional
recessiveness of pest alleles that confer resistance.
The biology of rice stem borers and the socioeconomics
of rice cultivation present a challenge to the design and
implementation of resistance management strategies for
Bt rice. Because most rice in Asia is grown on small farms
and extension services have limited reach and influence, it
will be difficult in most areas to establish and enforce a
policy of mandatory refuges. In addition, with minor
exceptions, the yellow stem borer and the striped stem
borer feed only on rice, so refuges will not be provided by
alternative host plants [40]. Governments can, however,
implement policies that might result in the maintenance of
adequate refuges [41]. First, governments can require that
Bt rice cultivars have two toxins, both produced at a high
dose and chosen such that a single insect mutation is
unlikely to confer resistance to both [42,43]. Such twotoxin
cultivars would require smaller refuges than would
single-toxin cultivars [42,44]. Biochemical studies have
identified several appropriate toxin combinations for rice
stem borers (e.g. Cry1Ab with Cry2A [45,46]). Because
four different cry genes have been transformed into rice
lines (cry1Ab, cry1Ac, cry1Ba and cry2A), a concerted effort
should be made to cross these lines to produce at least twotoxin
rice, if not three- or four-toxin rice (Table 1). Second,
governments can restrict the number of popular cultivars
that are released in Bt form and maintain seed supplies of
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non-Bt cultivars. Farmers who choose to grow non-Bt
cultivars would in effect be providing a refuge for
neighbouring fields planted with Bt cultivars. The nonBt
farmers would benefit from a possible area-wide
decrease in pest populations similar to the decrease in
pink bollworm populations in Bt-cotton-growing areas of
the southwestern USA [47].
Regulation and public policy
Research into GM crops is advancing rapidly in many
Asian countries, with over 100 private and publicly funded
laboratories working on improving crop quality and yields
in China alone [48]. China has acknowledged and
emphasized the importance of biotechnology in improving
agricultural crops since the late 1980s [8] (http://
yaleglobal.yale.edu/display.article?id¼2526). There have
been several successful field trials of Bt rice in China
[4,5,49] but commercialization of Bt rice has been delayed
by government officials. Following China’s admittance into
the World Trade Organization in December 2001, China
implemented strict regulations regarding the management
of biotechnology that have effectively delayed the
potential release of commercial Bt rice. One factor
currently delaying the release of transgenic rice by
many rice-producing countries is the prima facie
regulations (http://www.wto.org/english/res_e/booksp_e/
analytic_index_e/sps_03_e.htm) implemented by some
rice-importing countries, such as those of the European
Union, that restrict the import of GM food products.
There is thus a direct relationship between trade
policies in rice-importing countries and continued
insecticide consumption amongst rice producers. An
initial impediment to the development and release of
transgenic crops in Asia, the lack of national biosafety
regulations, is being overcome as more and more
countries implement biosafety frameworks. A second
probable factor is consumer acceptance. Rice is the
staple food for most Asians and occupies a unique
position in many cultures. Surveys indicate that most
consumers are not aware of transgenic crops [50],
presenting both a challenge and an opportunity to
governments, research institutions and companies
developing Bt rice. The successful introductions of Bt
cotton in China and India, and of Bt maize in the
Philippines [51] have demonstrated that these
countries have functioning regulatory systems for the
review and release of transgenic crops, and will provide
incentive for the eventual release of Bt rice. The
release of Bt rice would also be further expedited if
other transgenic rice cultivars are released first. It is
possible that ‘golden rice’ (with enhanced levels of
provitamin A) [52] and Xa-21 rice (containing a gene
for resistance to bacterial blight from the wild species
Oryza longistaminata) [53] will be the first transgenic
varieties approved for release.
Conclusion
The criteria for the successful deployment of Bt rice in Asia
include safety, sustainability and expeditiousness. Continued
research and development and evolution of the
regulatory environment are necessary if these criteria are
to be met (Box 1). Resistance management is the major
technical challenge for Bt rice. Given the monophagous
nature of rice stem borers and the limited ability to
influence farmer behaviour in most areas, how can
adequate refuges be maintained? Development and field
testing of rice containing two appropriate toxin genes, both
expressed at a high dose, continues to be a research
priority [42,54]. Only two reports of Bt rice lines pyramiding
two appropriate toxin genes (cry1Ac and cry2A) have
been published [55,56]. There is also a need for extensionists
to produce educational materials and programmes for
farmers to communicate the benefits of and best agronomic
practices for Bt rice. Although Bt crops have an excellent
record of environmental safety and compatibility with
biological control, monitoring of impacts on rice agroecosystems
will be essential when large-scale plantings of
Bt rice are approved.
The negative consequences of further delays in releasing
Bt rice include continued overuse of broad-spectrum
insecticides and their severe effects on farmer health,
biological pest control and environmental quality. Given
the disastrous state of rice paddy water quality caused by
disruptive chemical sprays, the gains in biodiversity alone
justify the implementation of extensive field trials. Our
own preliminary small-scale field trials have led to
encouraging observations of increased amphibian and
fish wildlife in rice paddy water where Bt rice is grown and
insecticide applications eliminated. In addition, there is an
ongoing need to increase rice yields to assure continued
food security in Asia.
It is known that Bt rice has the potential to increase
yields, to decrease pesticide applications and hence to
improve groundwater quality, and possibly also to reduce
mycotoxin levels. The substantial potential benefits
offered by Bt rice, particularly in light of the success of
Bt cotton and Bt maize, should be powerful motivators
for further development of improved Bt rice lines and
accelerated approval of the release of Bt rice to
farmers.
Acknowledgements
This article is dedicated to our mentor Ming Wei Gao on the occasion of his
80th birthday. We thank the Natural Sciences and Engineering Research
Council of Canada (I.A.), the Ministry of Science and Technology of China
(Q.Y.S.) and The Rockefeller Foundation (I.A., M.B.C., Q.Y.S.) for research
support, and the National Research Council of Canada for a WES
scholarship (S.M.H.). We thank the International Rice Research Institute
Box 1. Future research and regulatory needs for successful
deployment of Bt rice
† Resistance management strategies compatible with rice production
systems in Asia.
† High-dose Bt rice cultivars with two toxin genes, each of which
binds to a different receptor.
† Resistance monitoring programmes.
† Case-by-case evaluation of the possible impact of cry gene
outcrossing to wild and weedy rices.
† Studies of the fate of Cry toxins in tropical flooded soils.
† Programmes for monitoring the impact of large-scale Bt rice
plantings on biological control.
† Educational materials for farmers and consumers.
† Trade policies authorizing the importation of transgenic rice.
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for productive collaboration. We declare that we have no competing
financial interests.
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