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Integrated Pest Management of
Cassava Whiteflies
 An integrated pest management (IPM) program for cassava pests in
Valle del Cauca is being designed and implemented. Because farmers’ surveys show that
the predominant pest, for both small and large farmers, is whitefly, emphasis is being
given to the complex of whitefly species associated with the crop. At present, research
activities for whitefly control, many funded by the Colombian Ministry of Agriculture and
Rural Development (MADR),
include host-plant resistance, biological control, cultural practices, and chemical
control. CIAT and CORPOICA have
jointly developed a cassava variety that is resistant to whiteflies. Released in November
2002, this variety is expected to greatly aid small farmers to control this pest.
Various biological control agents, including predators, parasites,
and entomopathogens have been identified and are being evaluated. An isolate of the
entomopathogenic fungus Verticillium lecanii (CIAT 215) has shown highly positive
results in preliminary trials, and has the potential to be commercially formulated. A
predator species, Chrysopa sp., has been collected from whitefly infested cassava
fields, and is being mass reared in the laboratory. It will then be evaluated in the field
for whitefly control. Numerous parasitoid species of whiteflies have been identified in
field surveys in three countries (Colombia, Ecuador, and Venezuela) but their efficiency
in controlling high whitefly outbreaks is still being assessed.
A 2-month prohibition on growing cassava at CIAT’s Palmira
station dramatically reduced whitefly populations in subsequent plantings. The prohibition
is now recommended practice, especially for large-scale cassava farmers in Valle del
Cauca.
Most farmers, small or large, resort to pesticide applications to control whiteflies.
In a series of field trials, Confidor® (imidacloprid) gave the best results for
controlling cassava whiteflies, with Actara® (thiamethoxan) also giving favorable
results. However, a cost-benefit ratio study shows that, while pesticide use for larger
farmers is profitable because of a guaranteed higher price for cassava roots, it may be
uneconomical for small farmers. These results reinforce the idea that alternative methods
must be sought for whitefly control that are efficient and cost effective for the small
farmer, as well as being environmentally sound.
Contact: Anthony Bellotti
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Related Web Site |
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A Cassava Variety Resistant to
Whitefly
 Whitefly
resistance in agricultural crops is generally rare, and control usually requires the
continued use of agrochemicals. Pesticide use reduces farmers’ income, and is
especially detrimental to small farmers who do not have easy access to credit for
purchasing costly inputs. Host-plant resistance (HPR) offers a low-cost, efficient, and
easy-to-use technology for controlling major pests in cassava, such as whiteflies.
Several good sources of resistance to whiteflies have been
identified in cassava, and high-yielding, whitefly resistant, cassava hybrids are being
developed. The hybrid CG 489-31 (CIAT breeding code) is officially being released by CORPOICA in November 2002, under
the varietal name ‘Nataima-31’, probably the first of a food crop to be released
for whitefly resistance. This variety was developed over 15 years in a collaborative
effort between CIAT and CORPOICA. Especially for small cassava farmers,
‘Nataima-31’ is a high quality, high-yielding, cassava variety that will require
little or no pesticide use. It is also moderately resistant to thrips and mites.
Contact: Anthony
Bellotti
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Press Release:
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Cassava HCN Content and Burrower Bug Behavior
Because previous laboratory studies showed that adults and nymphs
of Cyrtomenus bergi feeding on a high-HCN cassava clone had increased mortality,
this study aimed to develop a bioassay, using a holidic liquid diet, for proving that high
HCN levels induce mortality in newly hatched larvae and adults of C. bergi. The
bioassay developed in this study should be useful in the future testing of other active
molecules on C. bergi.
Contact: Paul-André Calatayud
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Identifying Mealybug Populations
 The
ITS region of the mitochondrial 16S rDNA gene has been used in several studies on
phylogenetic relationships. At CIAT, we have used RAPD-PCR tools to identify different
mealybug populations and to characterize the ITS of the mitochondrial 16S rDNA gene from
four populations representing three species of mealybugs in Africa and South America.
Furthermore, PCR was used to detect Wolbachia bacteria in these populations. The
RAPDs developed in this study comprised a diagnostic method that can be used to rapidly
identify mealybug species.
Contact: Paul-André Calatayud
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Detecting a Phytoplasm Associated with
Frogskin Disease in Cassava (Manihot esculenta Crantz) in Colombia
 Frogskin (FSD) is an important cassava disease that affects roots. The causal
agent remains unknown, even though it has been reported with increasing frequency in
Colombia, Brazil, and Venezuela. Yield losses close to 90% have been reported in
commercial fields in Colombia.
The specific primers R16mF2/R16mR1 and R16F2n/R16R2 were used in a
nested PCR assay to detect and confirm that phytoplasms were associated with FSD. To
characterize and subsequently classify the phytoplasms, two pairs of universal primers
(P1/P7 and R16F2n/R2) were used to amplify the 16S rDNA gene. Root, stem, leaf, and flower
samples were taken from symptomatic plants, and 1.2-kb fragments amplified.
Sequence analysis of the cloned fragments revealed that the
phytoplasms found were similar to the Chinaberry yellows phytoplasm (GenBank acc. no.
AF495657, 16SrXIII Mexican periwinkle virescence group) and the Cirsium white
leaf phytoplasm (GenBank acc. no. AF373106, 16SrIII X-disease group), both with a sequence
homology of 100% and 99%, respectively.
The presence of phytoplasms was confirmed by the DAPI and
Dienes’ staining methods and by grafting. This is the first report of
phytoplasms associated with FSD in cassava.
Contact: Elizabeth
Alvarez
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Molecular Techniques for
Determining the Causal Agent of Cassava Frogskin Disease
Amplified fragment length polymorphism (AFLP) is a powerful tool used in molecular
marker studies for genetic traits. Given the difficulty in identifying the causal agent of
FSD, we decided to use this methodology. We found some fragments that amplified only for
cassava samples affected with FSD. One fragment was cloned and sequenced, and found to
have homology with the S1 species of rice ragged stunt virus (RRSV). Previously, we had
described a cDNA clone that had homology with the S5 species of RRSV. Now that we have
cloned two species of a virus with homology with RRSV, we can state that a new virus in
cassava has been found. Evidence suggests that this virus is associated with FSD, although
further studies are needed to clarify this association.
Contact: Lee Calvert
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