Whitefly and whitefly-borne viruses in the tropics : Building a ... - cgiar

CHAPTER 1.10
72
Madagascar
Introduction
Cassava mosaic disease (CMD), caused
by cassava mosaic begomoviruses
transmitted by the whitefly Bemisia
tabaci (Gennadius) and through virusinfected
planting material (Harrison,
1987), is the most important viral
disease of cassava (Manihot esculenta
Crantz) in Madagascar. The disease
was first reported in Madagascar in
1932, although it was of only minor
importance at this time (François,
1937). Epidemics were first reported in
1934, from an area to the west of Lake
Alatroa on the central plateau and,
between this time and the end of the
1930s, the epidemic spread to cover all
cassava-growing areas of the island
(Cours, 1951). Symptoms in local
varieties were very severe and cassava
cultivation was abandoned on a wide
scale. The impact was so great that the
government ordered urgent attention to
be given to the problem (Frappa, 1938)
and a major programme for the
development of resistant varieties was
initiated (Cours, 1951; Cours-Darne,
1968). The first of these varieties was
widely disseminated in the mid-1940s.
Since this time, CMD appears to have
* Laboratoire de Pathologie Végétale,
Ambatobe, Madagascar.
** International Institute of Tropical
Agriculture-Eastern and Southern Africa
Regional Center (IITA-ESARC), Kampala,
Uganda.
Whiteflies and Whitefly-borne Viruses in the Tropics
Sahondramalala Ranomenjanahary*,
Jocelyn Ramelison* and Peter Sseruwagi**
become a problem of relatively minor
significance.
Sweetpotato virus disease (SPVD)
results from co-infection of sweetpotato
(Ipomoea batatas [L.] Lam.) by whiteflytransmitted
Sweetpotato chlorotic stunt
virus and aphid-transmitted
Sweetpotato feathery mottle virus
(Gibson et al., 1998). SPVD has not
been reported as a major problem in
Madagascar, although the country is
one of the largest producers of
sweetpotato in Africa.
In order to provide a basic
understanding of the incidence of
whiteflies, CMD and SPVD in
Madagascar, a study was conducted in
four survey areas that represent the
major cassava and sweetpotato growing
areas: Antananarivo (central midaltitude
plateau), Fianarantsoa (eastern
humid coast), Toliara (south-western
semi-arid coast) and Mahajanga
(northern sub-humid coast) (Figure 1).
This initial phase of the study aimed at
documenting the status of whiteflies
and whitefly-transmitted viruses and at
describing producer knowledge of these
problems on cassava and sweetpotato,
with a view to prioritizing further
actions and eventually developing
integrated management strategies to
tackle the most serious problems
identified. The survey was carried out
during the months of June and August
1998.