During the year 2002, two new diseases with unknown etiologies were detected in cucurbit crops in Israel. One disease was detected in squash fields throughout the country, while the second appeared in a single watermelon plot in the south, just outside the city of Elat. The infected watermelon plot was eradicated, but nonetheless the new disease spread throughout the country and today it is present in all the watermelon production areas. Both diseases were associated with elevated whitefly populations. Indeed, it was found that both are transmitted only by whiteflies, and are incited by two begomoviruses. Both viruses were cloned and sequenced, and were identified as Watermelon chlorotic stunt virus (WmCSV) and Squash leaf curl virus (SLCV). The host range of the Israeli WmCSV isolate (WmCSV-IL) was determined and resembles the host range of the three other known WmCSV isolates (from Yemen, Sudan, and Iran), but with a few differences. Although no genetic resistance to WmCSV was observed in cultivated watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai], resistance to the virus was found in a wild relative, colocynth (Citrullus colocynthis (L) Schrader). Nucleotide sequence comparisons revealed that WmCSV-IL is highly homologous to other WmCSV isolates, with the highest homology (nearly identical) to the isolate from Sudan. SLCV-IL host range was determined as well, and was also found to be similar to other SLCV isolates. However, following genome sequencing, it was found that due to two separate point mutations, two viral open reading frames (ORF) were altered. The AC2 ORF was extended by 129 nucleotides, while the BV1 ORF was reduced by 99 nucleotides.
Grapevine rupestris stem pitting-associated virus (GRSPaV, genus Foveavirus, family Betaflexiviridae) is one of the most prevalent viruses in grapevines and is associated with three distinct diseases: rupestris stem pitting, vein necrosis and Syrah decline. Little is known about the biology and pathological properties of GRSPaV. In this work, we engineered a full-length infectious cDNA clone for GRSPaV and a GFP-tagged variant, both under the transcriptional control of Cauliflower mosaic virus 35S promoter. We demonstrated that these cDNA clones were infectious in grapevines and Nicotiana benthamiana through fluorescence microscopy, RT-PCR, Western blotting and immuno electron microscopy. Interestingly, GRSPaV does not cause systemic infection in four of the most commonly used herbaceous plants, even in the presence of the movement proteins of two other viruses which are known to complement numerous movement-defective viruses. These infectious clones are the first of members of Foveavirus which would allow further investigations into mechanisms governing different aspects of replication for GRSPaV and perhaps related viruses.
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