Iris yellow spot virus (IYSV), a new tospovirus associated with a disease in onion (Allium cepa) that is known to growers in Israel as “straw bleaching,” was identified and further characterized by host range, serology, electron microscopy, and molecular analysis of the nucleocapsid gene. The transmissibility of IYSV by Thrips tabaci and Frankliniella occidentalis was studied. IYSV was efficiently transmitted by T. tabaci from infected to healthy onion seedlings and leaf pieces. Two biotypes of F. occidentalis, collected from two different locations in Israel, failed to transmit the virus. Surveys to relate the incidence of thrips populations to that of IYSV were conducted in onion fields. They revealed that the onion thrips T. tabaci was the predominant thrips species, and that its incidence was strongly related to that of IYSV. Forty-five percent of the thrips population collected from IYSV-infected onion and garlic fields in Israel transmitted the virus. IYSV was not transmitted to onion seedlings from infected mother plants through the seed, and was not located in bulbs of infected plants.

Unusual viral symptoms were seen on lisianthus (Eustoma russellianum) grown in the Besor area in Israel. Symptoms included necrotic spots and rings on leaves and systemic necrosis. Preliminary analyses suggested that the disease was caused by a tospovirus. Virus particles typical of a tospovirus were observed with electron microscopy in samples taken only from symptomatic leaves. Double-antibody sandwich enzyme-linked immunosorbent assay tests of leaf sap, extracted from lisianthus and mechanically inoculated indicator plants, gave a strong positive reaction to Iris yellow spot virus (IYSV). Polyclonal antibodies prepared against IYSV enabled specific detection of the virus in crude sap from infected plants. Western blot analysis showed that IYSV was serologically distinct from Tomato spotted wilt virus (TSWV). Primers specific to the nucleocapsid gene of IYSV were used in a reverse transcription-polymerase chain reaction assay (RT-PCR) to verify the presence of IYSV. RT-PCR gave an expected PCR product of approximately 850 bp. The sequence of the cloned nucleocapsid gene confirmed the identity of IYSV, thus confirming IYSV infection of lisianthus. This is the first report of IYSV infection in dicotyledons.

In July 1999, Hibiscus esculentus plants, grown in garden plots in Galilee, Israel, exhibited chlorosis, vein clearing accompanied by necrosis, and growth reduction. All samples (n = 10) tested positive for Turnip mosaic virus (TuMV) in enzyme-linked immunosorbent assay (ELISA), using a polyclonal antibody produced in our laboratory against purified virus. Virus in crude sap extracted from symptomatic tissue was mechanically transmitted to Chenopodium quinoa, C. amaranticolor, Nicotiana tabacum Xanthi nc and White Burley, N. clevelandii, N. benthamiana, N. sylvestris, and N. rustica, all of which developed symptoms characteristic of TuMV infection (1). ELISA testing of leaf sap extracted from mechanically inoculated indicator plants gave a strong positive reaction to TuMV. Leaf dip preparations of H. esculentus were analyzed by transmission electron microscopy. Filamentous virus particles typical of a potyvirus were observed in samples from symptomatic leaves. General primer pairs, which cover the complete 3′-end of the potyvirus genome were used in a reverse transcription-polymerase chain reaction assay (RT-PCR), gave an expected amplification product of approximately 300 bp. The nucleotide sequence of the PCR product was 97% identical to the CP sequence of other TuMV, thus verifying TuMV infection of H. esculentus. This is the first report of H. esculentus infection by TuMV. Reference: (1) A. Gera et al. J. Phytopathol. 145:289-293, 1997.

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Conspicuous viral symptoms were seen on Tabernaemontana divaricata, a member of the family Apocynaceae, grown in a commercial nursery, in Israel. The symptoms varied widely and included chlorotic ringspots and banding, oak-leaf patterns and mosaic. At the end of the winter, large yellow spots, which later became necrotic, appeared on fully expanded leaves. The necrotic zones later fell out, leaving shot holes. Preliminary analysis suggested that the disease was associated with a tobamovirus. Particles typical of a tobamovirus were observed by electron microscopy only in samples taken from symptomatic leaves. A partial segment of the 5 ' -terminus of the viral RNA, which comprised of 533 bp was cloned and sequenced. Comparison of the predicted amino acid sequence with those of other tobamoviruses revealed 94% identity with Tobacco mild green mosaic virus (TMGMV) genome. Primers specific to the coat protein (CP) gene of TMGMV used in a reverse transcription-polymerase chain reaction assay (RT-PCR) gave an expected amplification product of 455 bp. The amino acid composition of the cloned CP gene, which shows a complete identity to that of TMGMV, confirmed the identity of TMGMV infecting Tabernaemontana. Polyclonal antibodies prepared against the virus and used in double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) enabled specific detection of the virus in crude sap extracted from T. divaricata and mechanically inoculated indicator plants. This is the first report of TMGMV infection in Tabernaemontana and the first incidence of the virus in Israel.