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Greenhouse-grown cucumber plants showed mosaic-type symptoms and irregular yellow spots on their leaves. The disease did not affect plant growth and the fruits remained symptom free. A virus having isometric particles, 30 nm in size, was isolated from the infected tissues and from recycled drainage water collected from tuff (volcanic rock) raised beds on which plants were grown. The virus was identified as a variant of cucumber leaf spot virus (CLSV) that has a host range similar but not identical to that of a previously described CLSV isolate. The overall nucleotide sequence identity between the RNAs of the Israeli isolate and the type isolate virus (accession numbers: DQ227315 and AY571334, respectively) amounts to 96%. [ABSTRACT FROM AUTHOR]

An indexing system for detecting Tomato mosaic virus (ToMV) in commercial tomato seed lots is described. Factors associated with the procedure were analyzed and the following standard two-step working scheme is proposed: (i) mass screening by ELISA for the presence of the virus; (ii) evaluation of virus infectivity within the infested seed lots. A threshold of 10 ng ml−1 was determined for detection of purified ToMV by either ELISA or plant inoculation. Nicotiana tabacum cv. Xanthi NN was found to be a highly sensitive local lesion assay plant for the detection of ToMV. A positive ELISA threshold (1.3 times above the non-specific background) was set for seed samples taken from commercial seed lots by testing the same samples by both ELISA and a bioassay. [ABSTRACT FROM AUTHOR]

Transgenic tomato plants carrying a truncated replication associated protein (T-Rep) gene of the mild strain of Tomato yellow leaf curl virus-Israel (TYLCV-Is [Mild]) were prepared. The transgene encoding the first 129 amino acids of Rep conferred resistance only against the virus strain from which it was derived, while these plants were susceptible to the severe strain of TYLCV-Is. This strain-specific effect may be the result of high sequence divergence within the N-terminal domains of the Rep genes of the two virus isolates which share a mere 78% sequence identity at the nucleotide level and 77% at the amino acid level. Although the transgenic tomato plants were totally resistant to whitefly inoculation with the mild strain of TYLCV-Is, agroinoculation with the same virus strain resulted in variable resistance responses in the tested plants: while 21% of plants were totally immune to the virus, 33% were susceptible and 46% expressed a wide range of intermediate resistance characteristics. The applicability of TYLCV-Is derived resistance in tomato is discussed. [ABSTRACT FROM AUTHOR]

Using the sequential PAGE method for detection of small circular RNA molecules we isolated a viroid from greenhouse-grown tomato plants exhibiting severe stunting in Israel. The viroid was transmitted to tomato and to several other solanaceous plants by graft and mechanical inoculation, but only tomato plants showed symptoms of disease. Cloning and sequencing revealed that the viroid RNA is composed of 363 nucleotides, has 92% identity with the type strain (Ivory Coast strain) of Tomato apical stunt viroid (TASVd) and 99% identity with the Indonesian strain of this viroid. The experimental host range of TASVd-Is differs significantly from that of the type strain of TASVd. The possible epidemiological consequences leading to TASVd spread in geographically distant areas are discussed. [ABSTRACT FROM AUTHOR]

Transfer of cucumber plants ( Cucumis sativus L.) from Speedling-type polystyrene trays or polystyrene trays with a vacuum-forming insert, into pots filled with perlite infested with Cucumber fruit mottle mosaic virus (CFMMV), resulted in high disease incidence. However, when the plants were removed from the trays into condensed peat cells or into perlite sleeves, prior to their introduction into the infested medium, infection by the virus was completely prevented. Our results strongly support the hypothesis that tobamovirus invasion into the root cells is via wounds inflicted through the disturbance of the root system during transplanting. Unwounded, newly formed roots that penetrated into the infested medium did not allow invasion by the virus. The use of condensed peat trays as well as perlite sleeves can serve as an efficient means to block soilborne epidemics of tobamoviruses in infested soils. However, this practice should be combined with sanitation of the greenhouse space to eliminate virus transmission via the aboveground parts of the plants. [ABSTRACT FROM AUTHOR]

The biological, serological, and molecular characteristics of a newly isolated L4 resistance-breaking isolate of Pepper mild mottle virus (PMMoV) were studied. The new pathotype of PMMoV is closely related to the Israeli pathotypes P1,2 and P1,2,3 of the virus; however, the mosaic symptoms caused by this new pathotype on pepper plants with an L4 genotype were more severe than the mild mosaic symptoms caused by other common pathotypes of the virus in susceptible plants. The predicted amino acid sequence of the putative coat protein (CP) of the newly described pathotype has two amino acid mismatches when compared with the CP of pathotype P1,2, leucine to glutamine at position 47, and alanine to glycine at position 87. The CP of the new pathotype has one amino acid mismatch when compared with P1,2,3, having alanine instead of glycine at position 87. Based on its biological characteristics, the new pathotype was designated P1,2,3,4 of PMMoV-Is. A method is described for the differentiation among the three PMMoV pathotypes using restriction cleavage analysis of reverse-transcription polymerase chain reaction products made from virus-infected plants. An additional unique MnlI site in the CP gene of the newly isolated P1,2,3,4 allows its distinction from the other two isolates, while BglI cleaved only products of the P1,2 pathotype. [ABSTRACT FROM AUTHOR]