The perspective of sweetpotato chlorotic stunt virus in sweetpotato production in Africa: a review

摘要

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 Trideurodes 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 originatedalong 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 compriselong 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 percent less than uninfected or unaffected controls in field trials; plants infected with SPCSV alone generally yielded c. 30 - 80 percent 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 Ipoinoea 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.