The Natural Occurrence, Transmission, Properties and Possible Affinities of Cowpea Mild Mottle Virus

Abstract

Cowpea mild mottle virus (CMMV), although thought to be of only local importance when first found in 1973 infecting cowpeas (Vigna unguiculata) in Ghana, has since been shown to have a very extensive geographical distribution and a wide natural host range. It occurs in Africa, Asia, South America and Oceania in tomato (Lycopersicon esculenturri) and a range of leguminous crops including cowpeas, groundnuts (Arachis hypogaea, soybean (Glycine max) and French beans (Phaseolns vulgaris). The virus has physico‐chemical properties resembling those of aphid‐borne carlaviruses; it has filamentous particles ca. 650 nm long which contain a single polypeptide of 31–33 KDa and single‐stranded RNA of 2. 5 × 106. Unlike carlaviruses, however, CMMV is transmitted in a non‐persistent manner by whiteflies (Bemisia tabaci) and the particles occur in vivo in characteristic brush‐like inclusions. It is also seed‐borne in some, but not all, cultivars of cowpea and soybean, but seed‐transmission is probably dependent upon the interaction of genotype, virus strain, time of infection and environmental factors. CMMV is serologically closely related to, and thus probably synonymous with, viruses previously designated groundnut crinkle, Psophocarpus necrotic mosaic, Voandzeia mosaic and tomato pale chlorosis. It is, however, serologically unrelated to 18 recognized carlaviruses; because it is also transmitted by whiteflies and induces the formation of unusual brush‐like inclusions, it is probably best left unclassified or tentatively placed in a sub‐group of the carlavirus group until the taxonomic significance of these features has been fully evaluated.

Assessment of the effect of rate and time of application of rice-husk powder as an organic amendment on cowpea (Vigna unguiculata L.,walp) inoculated with cowpea mottle virus

“…Leaves are distorted, reduced in size and a witches' broom syndrome is common. Yields may be reduced by more than 75% (Jeyanandarajah & Brunt, 1993). Indeed, Cowpea yield reductions of more than 75% have been reported (Shoyinka et al, 1978).…”

A carlavirus-specific PCR primer and partial nucleotide sequence provides further evidence for the recognition of cowpea mild mottle virus as a whitefly-transmitted carlavirus

“…However, unlike other members of the carlavirus group which are transmitted non-persistently by aphids [Foster, 1992], CMMV is unusual in that it is transmitted in a non-persistent manner by whiteflies (Bemisia tabaci) [Jeyanandarajah and Brunt 1993]. In addition, CMMV has several other unusual properties compared with other carlaviruses, which include, no serological relationships with 18 recognised members of the carlavirus group, and the induction of unusual brush-like intracellular inclusions in infected plants [Brunt et al, 1983].…”

“…This is confirmed by nucleotide sequence (958 nucleotides) from the 3' terminal region of CMMV RNA which contains a partial open reading frame (ORF) having high similarity with the coat proteins of other carlaviruses. The sequence also contains an 11.7K ORF at the 3' terminus, containing a 'zinc-finger' motif which is unique to carlaviruses.Cowpea mild mottle virus (CMMV) has physicochemical properties which resemble those of members of the carlavirus group, namely the presence of filamentous particles c. 650 nm in length, consisting of a coat protein of 31-33K and a single-stranded RNA of Mr 2.5 x 10 6 [Jeyanandarajah and Brunt, 1993]. However, unlike other members of the carlavirus group which are transmitted non-persistently by aphids [Foster, 1992], CMMV is unusual in that it is transmitted in a non-persistent manner by whiteflies (Bemisia tabaci) [Jeyanandarajah and Brunt 1993].…”

“…In addition, CMMV has several other unusual properties compared with other carlaviruses, which include, no serological relationships with 18 recognised members of the carlavirus group, and the induction of unusual brush-like intracellular inclusions in infected plants [Brunt et al, 1983]. It has been suggested that CMMV remain unclassified until the taxonomic significance of these differences have been investigated further [Jeyanandarajah and Brunt, 1993].We report here attempts to develop a rapid and specific identification test for carlaviruses which can also be used to determine whether CMMV and similar unclassified viruses are species of the carlavirus genus. The test is based on the polymerase chain reaction (PCR) using primers to conserved and unique sequences in carlavirus RNAs.…”

“…In addition, CMMV has several other unusual properties compared with other carlaviruses, which include, no serological relationships with 18 recognised members of the carlavirus group, and the induction of unusual brush-like intracellular inclusions in infected plants [Brunt et al, 1983]. It has been suggested that CMMV remain unclassified until the taxonomic significance of these differences have been investigated further [Jeyanandarajah and Brunt, 1993].…”