Sweetpotato chlorotic stunt virus (SPCSV) (Crinivirus: Closteroviridae)
occurs in the main tropical regions of the World and is probably the most damaging
pathogen of sweetpotato (
Ipomea batatas
). However, until recently,
little research had been done on it. The methods of identification were inadequate
and this led to synonymy. The virus is transmitted by the whitefly species,
Bemisia tabaci
and
Trialeurodes abutilonea
, in a semi-persistent
fashion. At least two serotypes occur, one, first described from West Africa (SPCSV
WA
), and the other first described from East Africa (SPCSV
EA ). Both
serotypes have also been found in the Americas. Nucleotide sequencing has facilitated
the process of distinguishing strains. The SPCSV may have originated along with
sweetpotato in the Americas, but is perhaps more likely to have been a 'new
encounter' for sweetpotato when it was introduced to Africa and elsewhere
in the 'Old World'. It infects few plant species other than
Ipomoea
spp. The virions comprise long flexuous particles and the genome is RNA and bipartite.
Geographically, isolated strains of SPCSV have been distinguished using serological-
and nucleic acid-based methods. The virus synergises Sweetpotato feathery mottle
virus (SPFMV) (Potyvirus: Potyviridae), leading to increased titres of this virus
and the development of the severe disease sweetpotato virus disease (SPVD) in
dually infected sweetpotato plants. Plants affected by SPVD following artificial
or natural infection with SPCSV plus SPFMV have generally yielded
c.60
-90% less than uninfected or unaffected controls in field trials; plants
infected with SPCSV alone generally yielded
c.30 - 80% less. However,
in crops, compensatory growth by unaffected neighbouring sweetpotato plants probably
results in direct effects on overall crop yields being small, and the major effect
of SPCSV in constraining the yields of sweetpotato is perhaps through preventing
the cultivation of high yielding but SPVD-susceptible sweetpotato cultivars. Breeding
resistant high-yielding varieties has been the main means of avoiding the deleterious
effects of SPVD. Although sweetpotato cultivars which have field resistance to
SPCSV have been identified, no gene conferring immunity to SPCSV has been identified
within sweetpotato or its close relatives. Cultivars non-indigenous to Africa
seem particularly susceptible. Extreme resistance has been identified in certain
wild
Ipomoea
spp. Recent epidemiological studies indicate that
most spread of SPCSV is short distance, leading to interest in the use of phytosanitation
measures to grow high-yielding but somewhat SPVD-susceptible cultivars. This paper
comprises a review of research work done on SPCSV world wide dating from 1939
to-date.
