Garlic (Allium sativum) is an important crop in several states of India. Filamentous viruses such as Onion yellow dwarf virus (OYDV), Shallot latent virus (SLV), and Garlic common latent virus (GarCLV) have been reported previously in different garlic cultivars from India (4). These viruses are transmitted from generation to generation through cloves and cause severe reduction in yield and quality. During December 2010, garlic plants were observed with mosaic leaf symptoms and stunting in an experimental field at the Indian Agricultural Research Institute, Delhi. Cloves and leaves from 3-month-old symptomatic plants of five different cultivars (G-282, IC-375416, Ruag, Yamuna Safed, and ACC-40), originally from different regions of India, were collected from the field in Delhi and total RNA was extracted using an RNeasy Plant Mini Kit (Qiagen, Valencia, CA). The presence of OYDV and GarCLV was confirmed by reverse transcription (RT)-PCR in all cultivars, while the presence of SLV was only confirmed in cv. G-282 by RT-PCR. Since Allexiviruses are common in garlic, their detection in cloves was confirmed by RT-PCR using primers ALLEX 1 and ALLEX 2 (2). An ~200-bp amplification product was observed in all five cultivars. To further characterize the Allexivirus in these cultivars, an amplicon of ~900 bp was amplified with Allex-CP (1) and ALLEX 2 (2) primers and cloned and sequenced. BLAST analysis of the nucleotide sequences from five garlic cultivars showed identity with different allexiviruses, Garlic virus A (GarV-A) (74 to 83%), Garlic virus E (GarV-E) (74 to 80%), Garlic virus D (GarV-D) (76 to 79%), and Garlic virus X (GarV-X) (75 to 78%). Since species demarcation in the genus Allexivirus is based on the coat protein (CP) gene (3), another set of primers, 5′-MYT KGA GTG GCT VAC ACA YAT-3′ and 5′-ATT RAA GTC GTG RGG ATG CAT-3′ was designed. These primers were derived from conserved regions of ORF4 and ORF5 (CP) sequences of allexiviruses available in the NCBI database and used in RT-PCR to obtain the complete CP. An ~1.5-kb amplicon was obtained only in cv. G-282 that originated from the southern part of India. A similar amplicon was obtained from Chenopodium amaranticolor mechanically inoculated with leaf sap from cv. G-282. Sequences (1,422 bp) obtained from three clones each from garlic cv. G-282 and C. amaranticolor were identical and BLAST analysis of the consensus nucleotide sequence showed maximum identity of 75 to 81% with isolates of GarV-X. The 1,422 nucleotide sequence was comprised of 690 bp of ORF4 (partial) and 732 bp of the CP. The coat protein sequence (GenBank Accession No. HQ822272) shared a 79.6 to 81.1% identity in nucleotide and 89.3 to 90.9% in amino acid sequence with different isolates of GarV-X (GenBank Accession Nos. AJ292229, U89243, and GQ475426). To our knowledge, this is the first report of GarV-X in a garlic cultivar from India. The characterization and identification of allexiviruses is important for production of virus-free garlic plants through tissue culture in India.
References: (1) J. Chen et al. Arch. Virol. 149:435, 2004. (2) C. I. Dovas et al. J. Phytopathol.149:731, 2001. (3) C. M. Fauquet et al. Virus Taxonomy-VIIIth Report of the ICTV, Academic Press, London, 2005. (4) S. Majumder and V. K. Baranwal. Plant Dis. 93:106, 2009.
