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SUMMARYComplementary DNA (cDNA) of citrus tristeza virus (CTV) RNA, synthesized using calf thymus DNA random primers, was converted to a double-stranded form and inserted into the PstI site of the Escherichia coli pBR322 plasmid by the G-C tailing method. Bacterial clones harbouring virus-specific sequences were detected by colony hybridization with a 32p-labelled viral RNA probe. Hybridization patterns of denatured virus RNA revealed the presence of three types of specific clones: those hybridizing with a distinct narrow band corresponding to the full-length virus RNA, those hybridizing with a broader band of virus RNA sequences, and those hybridizing with several distinct virus-related RNA bands. Similar patterns were obtained when these clones were hybridized to purified double-stranded RNA from CTV-infected plants. None of these cDNA clones hybridized with similarly treated preparations extracted from healthy plants. The origin of variation among the CTV clones is discussed.

The nucleotide sequence of the 3' terminal region of potato virus Y (PVY) was determined. Starting with a poly(A) tail of 18 residues a non-coding region of 335 nucleotides precedes the region encoding for the virus coat protein (cp) 801 nucleotides long ending with a TGA. This region was located by comparing the predicted amino acid sequence with the one determined for the PVY capsid protein by Shukla et al. (1). Both sequences contained 267 amino acids sharing about 94% homology. They differ, however, at several positions presumably due to base transitions within their respective nucleotide sequences. Restriction endonuclease sites in and around the cp coding region were identified.

Symptoms typical of a phytoplasma infection were observed on a large number of Limonium hybrids in Israel in October 2000. Phytoplasma infection was confirmed by electron microscopy and polymerase chain reaction analysis. To identify the agent of pathogen spread surveys were made of candidate leafhoppers vectors in Limonium hybrid crops: one known phytoplasma vector (Orosius orientalis (Matsumura)) was present in very large numbers, ≈10-fold greater than any other species; three other known vectors were present in low to moderate numbers (Circulifer haematoceps complex (Mulsant et Rey), C. tenellus complex (Baker) and Exitianus capicola Stål); individual specimens of other vectors were occasionally found. Field collected specimens of these four species were shown to vector phytoplasma to healthy Limonium hybrid seedlings; this is the first time E. capicola has been shown to be a phytoplasma vector. A laboratory colony of O. orientalis was additionally shown to be able to acquire the phytoplasma from infected Limonium hybrids and subsequently vector it to healthy seedlings.

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