Soybean blotchy mosaic virus, a New Cytorhabdovirus Found in South Africa.

A previously unidentified plant Rhabdovirus sp. associated with a blotchy mosaic symptom of soybean (Glycine max), prevalent in the lower-lying, warmer soybean production areas of South Africa, was isolated and partially characterized. The virus was shown to be transmitted by mechanical inoculation and at least one species of leafhopper (Peragallia caboverdensis Lindberg (Cicadellidae, Agalliinae)). To determine the morphology and virion size, as well as intercellular accumulation, negative-stained preparations or embedded ultrathin sections of infected plant samples were observed under a transmission electron microscope. The distribution of the virions within the cytoplasm and its bullet-shaped morphology and size (338 to 371 nm by 93 nm) suggested that it is a putative member of the genus Cytorhabdovirus. Degenerate primers designed to a conserved region of the polymerase gene of a number of Rhabdovirus spp. were used in reverse-transcriptase polymerase chain reaction with total RNA from symptomatic plants as template. Amplicons were sequenced and compared with related sequences available on GenBank. The analysis confirmed that the virus was related to Cytorhabdovirus spp., with the highest nucleotide similarity being 60.7% with Northern cereal mosaic virus. The particle morphology, typical virion accumulation in the cytoplasm of infected cells, nucleotide sequence similarity with that of other plant Rhabdovirus spp., and unique symptoms on soybean suggest that the virus is a previously unknown Cytorhabdovirus sp., for which we propose the name Soybean blotchy mosaic virus (SbBMV).

Transmission of Activated-Episomal Banana streak OL (badna)virus (BSOLV) to cv. Williams Banana (Musa sp.) by Three Mealybug Species.

Four different mealybug species (Dysmicoccus brevipes, Planococcus citri, P. ficus, and Pseudococcus longispinus) were evaluated for their ability to transmit putative activated-episomal Banana streak OL (badna)virus (BSOLV) to banana cv. Williams (Cavendish subgroup, AAA). Expressible endogenous sequences of banana streak viruses (BSVs) have been reported to be present in the DNA of various Musa hybrids, including FHIA-21 (AAAB). To obtain activated episomal BSOLV for this experimental transmission study, intentional stress by tissue culture propagation was applied to indexed FHIA-21 which, while free of other viruses, can contain activated episomal BSOLV. Immunocapture polymerase chain reaction and triple-antibody sandwich enzyme-linked immunosorbent assay results revealed that 13.4% of the derived progeny of the mother plants were infected with episomal BSOLV. Four of these BSOLV-infected progeny were used as sources of episomal virus for transmission studies. D. brevipes, Planococcus citri, and P. ficus mealybugs were able to transmit the putative activated episomal BSOLV. Control plants for the transmission experiments included FHIA-21 corms with no background history of tissue culture, as well as virus-free Williams plants. Episomal Banana streak GF (badna)virus (BSGFV) was transmitted from asymptomatic corm-derived FHIA-21 plants by P. citri and P. ficus. This is the first report of P. ficus as a vector of BSVs.

First Report of Cucumber Mosaic Cucumovirus Subgroup 1 in South Africa, from Banana with Infectious Chlorosis.

Cucumber mosaic cucumovirus (CMV) is the etiological agent of infectious chlorosis disease in bananas (Musa spp.). In South Africa, diagnosis of CMV on banana has been based only on symptoms (1). A Grande Naine (Cavendish, AAA) plant with typical infectious chlorosis disease was obtained from Letsitele. Sap from this plant was inoculated to indicator plants. Virus was isolated by two serial local lesion transfers on Chenopodium quinoa and maintained on Nicotiana benthamiana. It was identified as a subgroup I CMV based on its reaction to CMV DTL-, but not CMV ToRS- monoclonal antibodies in double antibody sandwich (DAS)-enzyme-linked immunosorbent assay (ELISA). The identity was further confirmed by the polyhedral particle morphology under the electron microscope by negatively staining, and decoration in immunoelectron microscopy with antiserum to a local tomato isolate of CMV. Infectious chlorosis disease symptoms were induced by sap inoculation to healthy Grande Naine plants, and the virus detected by ELISA. This is the first confirmed diagnosis of CMV on bananas in South Africa. The isolate was deposited in the PPRI Virus Collection. Reference: (1) B. Q. Manicom. 1993. Pages 102-103 in: Handbook of banana growing in South Africa. J. C. Robinson, ed. Agric. Res. Counc., Inst. Trop. Subtrop.Crops, Nelspruit, South Africa.