Squash leaf curl virus (SLCV): a serious disease threatening cucurbits production in Palestine

The incidence of squash leaf curl disease and molecular characterization of the Palestinian isolate of Squash leaf curl virus [SLCV-(PAL)] are described in this study. Symptomatic leaf samples obtained from squash (Cucurbita pepo), watermelon [Citrullus lanatus (Thunb.)], and cucumber (Cucumis sativus L.) plants were tested for SLCV-[PAL] infection by PCR and RCA. SLCV was also found to occur naturally in Chenopodium murale, Convolvulus sp, and Prosporis farcta which showed yellowing. The disease incidence was 85 % in samples collected from Nablus in summer season, while it was 98 % in samples collected from Qalqilia in autumn. On the other hand, SLCV incidence did not exceed 25 % in winter season. The full-length DNA-A and DNA-B genomes of SLCV-[PAL] were amplified and sequenced, and the sequences were deposited in the GenBank. Sequence analysis reveals that SLCV-[PAL] is closely related to other isolates from Lebanon (SLCV-LB2), Jordan (SLCV-JO), Israel (SLCV-IL), and Egypt (SLCV-EG). DNA-A of SLCV-[PAL] showed the highest nucleotide identity (99.4 %) with SLCV-JO, and SLCV-LB2, while DNA-B had the highest nucleotide identity (99.3 %) with SLCV-IL. However, following genome sequencing, it was found that due to two separate point mutations, two viral open reading frames (ORF) were altered in some SLCV Palestinian isolates. The AC2 ORF was extended by 141 nucleotides, while the AC4 ORF was extended by 36 nucleotides.