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Two novel mastreviruses (genus Mastrevirus; family Geminiviridae), with proposed names chickpea chlorosis virus (CpCV) and chickpea redleaf virus, are described from chickpea (Cicer arietinum) from eastern Australia. The viruses have genomes of 2,582 and 2,605 nucleotides, respectively, and share similar features and organisation with typical dicot-infecting mastreviruses. Two distinct strains of CpCV were suggested by phylogenetic analysis. Additionally, a partial mastrevirus Rep sequence from turnip weed (Rapistrum rugosum) indicated the presence of a distinct strain of Tobacco yellow dwarf virus (TYDV). In phylogenetic analyses, isolates of Bean yellow dwarf virus, Chickpea chlorotic dwarf Pakistan virus and Chickpea chlorotic dwarf Sudan virus from southern and northern Africa and south-central and western Asia clustered separately from these three viruses from Australia. An Australian, eastern Asian, or south-eastern Asian origin for the novel mastreviruses and TYDV is discussed.

In 1999, banana streak disease outbreaks occurred at two locations in Australia in new banana hybrids that were being screened for fusarium wilt resistance. Two different badnaviruses, banana streak GF virus and a newly discovered virus called banana streak IM virus (BSIMV), were detected in these plants. The complete nucleotide sequence of the BSIMV genome was determined and comprised 7768 nt. Three open reading frames were detected, the first beginning with a non-conventional start codon (CUG). A 55-nt repetition in the putative pregenomic RNA promoter was also identified. Phylogenetic analysis suggests that BSIMV is most closely related to banana streak VN virus.

SUMMARYDouble-stranded RNA (dsRNA) has been isolated from bananas infected with banana bunchy top disease (BBTD) but not from healthy bananas of the same cultivar. Four major dsRNA species were present in seven different extracts and these had molecular weights of 4.40 x 10 6, 1.35 x 10 6, 0"50 × 106 and 0.48 x 106. This pattern of dsRNA species is similar to that in extracts from plants infected with barley yellow dwarf virus or beet western yellows virus strain ST9. The amount of extractable BBTDspecific dsRNA was affected by the temperature at which the infected plants were incubated and the interval between infection and harvest. The maximum amount of dsRNA was obtained from plants incubated at 30 °C and harvested 23 days after inoculation.Banana bunchy top disease (BBTD) is a severe disease of banana plants in many countries of the Asian-Pacific Basin as well as North Africa and India. In Australia, BBTD virtually destroyed the banana industry in the late 1920s and the industry now exists because of a vigorous but expensive inspection and eradication scheme. The cause of BBTD is thought to be a virus, probably a luteovirus (Matthews, 1982) because it is persistently transmitted by the banana aphid, Pentolonia nigronervosa, and diseased plants have yellowed leaves and damaged phloem (Magee, 1940). However, despite numerous attempts by many different workers to extract and characterize virus particles from BBTD plants, this has not been accomplished. In this paper, we report that we have isolated double-stranded RNA (dsRNA) from BBTD plants. This evidence also indicates that BBTD is caused by a virus, most probably a luteovirus.The isolate of BBTD used in this study was collected at Currumbin, Queensland, Australia and was maintained, by aphid transfer using Pentolonia nigronervosa, in plantlets derived vegetatively from a single cultured banana plant, Musa sapientum cv. Cavendish, regenerated from callus. The method used to extract dsRNA from banana plants was similar to that of Morris & Dodds (1979). Whole plants were harvested, frozen in liquid nitrogen and ground to a fine powder. The ground tissue (100 g) was shaken for 1 h at 4 °C in 400 ml 50 mM-Tris-HC1 pH 7.0, 100 mM-NaC1 and 1 mM-EDTA (STE), 200 ml water-saturated phenol containing 0.1 8-hydroxyquinoline, 200 ml chloroform, 50 ml 10~ SDS and 5 ml 2-mercaptoethanol. The mixture was centrifuged at 7000 g for 15 min and the aqueous phase was collected. Ethanol was added to it while stirring to give a final concentration of 15~. Whatman CF-11 cellulose was then added (0.15 g/g of original tissue) and the suspension was stirred under vacuum for 15 min at room temperature. The suspension was then poured into a chromatography column and washed with STE containing 15 ~ ethanol until the A zs4 of the eluate was that of STE containing 15 ~o ethanol. This normally required washing with 10 ml STE containing 15 ~ ethanol for each gram of tissue extracted. Double-stranded RNA was then eluted by washing with STE alone and precipitated by adding 2.5 vol. ethanol an...

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