FIRST REPORT OF GARLIC VIRUS D INFECTING ONION IN INDIA

Abstract

Onion (Allium cepa L.), a major vegetable crop of which India is the second largest producer in the world, is affected by more than 20 viruses of the genera Allexivirus, Carlavirus, Potyvirus, and Tospovirus (Maliogka et al., 2006). Plants with mild mosaic, or mild chlorotic stripes, or no symptoms were collected in March 2014 from the vegetable research farm of Punjab Agricultural University. Five of 10 plants tested by ELISA using an Onion yellow dwarf virus (OYDV) specific antiserum (Agdia, USA) gave a positive reaction. Because mite-borne allexiviruses infect Allium species around the world (Perotto et al., 2010), the same 10 plants were tested using primers Allex1 and Allex2 (Dovas et al., 2001). Of the eight positive samples, four were also OYDV-positive. PCR amplicons of 200 bp were purified using Nucleospin Gel and PCR clean-up kit (Macherey-Nagel, Germany), and cloned into pGEM-T easy vector (Promega, USA). Sequences from all eight were identical showing 86% nucleotide (nt) identity with Garlic virus D (GarVD) (KF550407) and 94% with Shal- lot virus X (M97264). A combination of Allex-cp(+) (Chen et al., 2004) and Allex2 was used in PCR, which generated a 900 bp amplicon from the coat protein/nucleic acid bind- ing protein (CP/NABP) region of allexiviruses. The cloned amplicons (KR534889) showed 87% overall nt identity and 94% amino acid identity to the CP and 86% to the NABP regions of a GarVD isolate (HQ681944) from Iran. Plants infected with GarVD showed mild chlorotic stripe, while those doubly infected with both OYDV and GarVD showed mosaic. To the best of our knowledge, this is the first report of GarVD from onion in India.