First Report on the Association of Squash leaf curl virus and Watermelon chlorotic stunt virus with Tomato Yellow Leaf Curl Disease
Authors: Ahmad F. Haj , Odeh W. , Anfoka G. 
Published: November 2012

Tomato (Solanum lycopersicum Mill.) is one of the most economically important vegetable crops in Jordan. Tomato cultivation in many countries in the Mediterranean basin is affected by several virus species belonging to Tomato yellow leaf curl virus complex (3). In March 2011, a field experiment was conducted at Horet Al-Sahen region to screen tomato breeding lines for resistance against TYLCD. Unexpectedly, severe TYLCD symptoms, including leaf curling, yellowing, and severe stunting were observed on some plants belonging to the F5 generation of a breeding line that was supposed to be resistant to the virus. One symptomatic plant was transferred into the greenhouse and used for whitefly transmission. The virus isolate was maintained on a susceptible tomato landrace by serial transmission using biotype B of the whitely vector (Bemisia tabaci). To confirm begomovirus infections, total nucleic acids were extracted from leaf tissues as previously described (4) and viral DNA genomes were amplified by rolling circle amplification (RCA) using the TempliPhi Amplification Kit (GE Healthcare). RCA products were then subjected to restriction digestion with different enzymes. Two DNA fragments of 1,035 bp and 1,760 bp were the products of EcoRl-digestion. Following sequencing, BLASTn analysis showed that the small fragment (1,035 bp) (GenBank Accession No. JX444576) corresponding to nts 2,408 to 2,690 of Watermelon chlorotic stunt virus from Jordan (WmCSV-[JO]) (EU561237) had approximately 99% nt identity with WmCSV-[JO] and other isolates from Israel (EF201809) and Iran (AJ245652), while the second fragment (1,760 bp) which corresponds to nts 117 to 1,877 of TYLCV genome had 98% nt identities with the Mexican isolate of TYLCV (FJ609655). Two pairs of primers (TYLCV29F1: TATGGCAATCGGTGTATC/TYLCV29R1: GTGTCCAGGTATAAGTAAG) and (TYLCV29F2: GAGAGCCCAATTTTTCAAG/TYLCV29R2: GGGAATATCTAGACGAAGAA) were used to amplify full TYLCV genome. Sequence analysis showed that TYLCV (JX444575) had the highest (98%) nt identity with the Mexican isolate of TYLCV (FJ609655). Because Squash leaf curl virus and WmCSV were recently reported in Jordan (1,2), we further investigated whether SLCV was also involved in the disease; therefore, two pairs of SLCV-specific primers (SLCVF-Sal (TATAGTCGACGTTGAACCGGATTTGAATG)/SLCVR-Sal (TATAGTCGACCTGAGGAGAGCACTAAATC) (DNA-A) and SLCVF-Hindlll (ATTAAAGCTTAGTGGTTATGCAAGGCG)/SLCVR-Hindlll (ATTAAAGCTTGGCTGCACCATATGAACG) (DNA-B) were used in PCR using RCA products as template. The expected sizes of DNA-A (2,639 bp) (JX444577) and DNA-B (2,607 bp) (JX444574) could successfully be amplified from the original symptomatic plant. Phylogenetic analysis showed that DNA-A was closely related to SLCV isolates from Lebanon (HM368373) and Egypt (DQ285019) with 99% nt identity, while DNA-B had highest nt identity (99%) with the Israeli isolate of SLCV (HQ184437). To our knowledge, this is the first report on the association of SLCV and WmCSV with TYLCD. Further studies will be carried out to investigate whether tomato can act as an inoculum source for these two viruses.

References: (1) A. Al-Musa et al. J. Phytopath. 156:311, 2008 (2) A. Al-Musa et al. Virus Genes 43:79, 2011. (3) G. Anfoka et al. J. Plant Pathol. 90:311, 2008. (4) J. L. Potter et al. Plant Dis, 87:1205, 2003.