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First report of onion yellow dwarf virus infecting onion in Ecuador

Abstract:

Onion (Allium cepa L., family Liliaceae) is one of the most important vegetable crops worldwide. Among all onion diseases, yellow dwarf disease caused by Onion yellow dwarf virus (OYDV) causes significant yield losses (Conci et al., 2003). OYDV (genus Potyvirus, family Potyviridae) is transmitted by aphids in a non-persistent manner and has a host range limited to Allium species and Narcissus. In July 2015, onions with irregular yellow striping, downward leaf curling, and plant stunting were observed in the Tungurahua province of Ecuador. Symptomatic (n = 10) and healthy onion samples were screened by double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) with OYDV polyclonal antibodies (Agdia, USA). All symptomatic onion samples reacted positively to OYDV antibodies in DAS-ELISA. Total RNA was isolated from a single plant with Triazol (Sigma, USA) and used in RT-PCR to amplify a DNA fragment of ca. 350 bp with universal primers designed in the potyviral NIb domain (Zheng et al., 2008). The amplicon was sequenced and the sequence (329 bp, GenBank accession No. KT590400) was analysed by BLAST and compared with the corresponding sequence of OYDV isolates from different countries. The partial NIb gene sequence of isolate OYDV-Ecuador showed a 91.1% and 98.1% maximum identity at the nucleotide and amino acid levels with isolates from Germany ((JX433020) and Italy (KF623533), respectively. A phylogenetic tree constructed with MEGA version 4.1 showed that the OYDV isolate from Ecuador was closely related to isolates from Germany, Italy, Argentina (JX433019) and USA (NC005029), all forming one cluster, whereas isolates from India (FR873734), Poland (KF862691), Japan (AB000474), Egypt (KT225546) and South Korea (AY390253) formed a separate cluster. To the best of our knowledge, this is the first report of OYDV on onion in Ecuador.