First Detection of <i>Cotton leaf curl Burewala virus</i> and Cognate <i>Cotton leaf curl Multan betasatellite</i> and <i>Gossypium darwinii symptomless alphasatellite</i> in Symptomatic <i>Luffa cylindrica</i> in Pakistan (2013)

Cotton leaf curl disease (CLCuD) is the major plant viral constraint to cotton production on the Indian subcontinent (2). CLCuD is primarily caused by begomovirus, Cotton leaf curl Burewala virus (CLCuBuV), and Cotton leaf curl Multan betasatellite (CLCuMB). During 2011 in Burewala, Pakistan, plants in a production field of Luffa cylindrica (Ghia tori) were infested with the whitefly Bemisia tabaci (Genn.), and ~60% of the plants exhibited leaf curling and stunting symptoms, reminiscent of those caused by begomoviruses (Geminiviridae). Total DNA was extracted from five different symptomatic leaf samples using the CTAB method (1), and extracts were analyzed by Southern blot hybridization. As a probe, we used a 1.1-kbp fragment of CLCuBuV and a positive signal was obtained from all five samples. Total DNA was used as template for rolling circle amplification (RCA) using the TempliPhi DNA Amplification Kit (GE Healthcare, Little Chalfont, United Kingdom). The amplified RCA products were digested with EcoRI, and the resulting ~2.7-kbp fragments from each isolate were directionally cloned into the EcoRI digested, pGEM-3Zf+ (Promega, Madison, WI) plasmid vector. PCR was used to amplify the prospective, associated betasatellite and alphasatellite molecules using the primers BetaF5'-GGTACCGCCGGAGCTTAGCWCKCC-3' and BetaR5'-GGTACCGTAGCTAAGGCTGCTGCG-3', and AlphaF5'-AAGCTTAGAGGAAACTAGGGTTTC-3' and AlphaR5'-AAGCTTTTCATACARTARTCNCRDG-3', respectively. The putative satellite amplicons, at ~1.4 kbp each were cloned in the plasmid vector pGEMT-Easy (Promega, Madison, WI) and sequenced. BLASTn comparisons of the apparently full-length begomoviral genomes, at 2,753 nt, against the NCBI database revealed that all five isolates were most closely related to CLCuBuV (FR750321). In addition, one each of beta- and alpha-satellite were amplified from all five samples at 1,393 and 1,378 bases, respectively. The beta- and alpha-satellites were most closely related to CLCuMB (HE985228) and the Gossypium darwinii symptomless alphasatellite (GDaSA) (FR877533), respectively. Pairwise sequence comparisons of the top 10 BLASTn hits using MEGA5 indicated that the helper begomovirus shared 99.9% identity with CLCuBuV (FR750321), the most prevalent helper virus currently associated with the leaf curl complex in Pakistan. Based on the ICTV demarcation for begomoviral species at <89%, it is considered a variant of CLCuBuV. The resultant beta- and alpha-satellite sequences were 98.1% and 97.8% identical to CLCuMB (HE985228) and GDaSA (FR877533), respectively, and are the most prevalent satellites associated with the CLCuD complex in Pakistan and India (2). To our knowledge, this is first report of the CLCuBuV-CLCuMB-GDaSA complex infecting a cucurbitaceous species, and the first report of L. cylindrica as a host of the CLCuD complex. This discovery of CLCuBuV and associated satellites in a cucurbitaceous host that is widely grown in Pakistan and India where this complex infects cotton indicates that the host range of CLCuBuV is broader than expected. This new information will aid in better understanding of cotton leaf curl disease epidemiology in the current epidemic areas. References: (1) J. J. Doyle and J. L. Doyle. Focus 12:13, 1990. (2) S. Mansoor et al. Trends Plant Sci. 11:209, 2006.