February 17, 2005
Source: American Phytopathological Society, Plant Disease Notes [edited]

First report of onion yellow dwarf virus, leek yellow stripe virus, and garlic common latent virus in garlic in Washington State
H. R. Pappu, Department of Plant Pathology, Washington State University, Pullman 99164; B. C. Hellier and F. M. Dugan, USDA-ARS, Western Regional Plant Introduction Station, Washington State University, Pullman 99164. Plant Dis. 89:205, 2005; published on-line as DOI: 10.1094/PD-89-0205C. Accepted for publication 23 Nov 2004.

Washington State ranks 4th in the country in garlic (_Allium sativum_) production (2). The impact of viruses on garlic production may be significant in Washington State, but little is known about the occurrence or identity of specific viruses (2). The USDA-ARS Western Regional Plant Introduction Station (WRPIS) collects, maintains, and
distributes garlic accessions. As part of the regeneration process, accessions are grown in field conditions at the WRPIS farm in Pullman, WA.

In June 2004, several WRPIS accessions developed symptoms indicative of viral infection, primarily chlorotic spots and yellow stripes on leaves and scapes. Cultivars Georgia Fire and Georgia Crystal showed more than 90 percent incidence of symptomatic plants. Some chlorotic spots appeared similar to those caused by Iris yellow spot virus on other _Allium_ spp. such as _A. cepa_.

However, enzyme-linked immunosorbent assay (ELISA), as well as polymerase chain reaction (PCR) with IYSV-specific primers (1) did not reveal the presence of IYSV. Degenerate, group-specific primers to potyviruses (3) and carlaviruses (courtesy of S. D. Wyatt) were used on total nucleic acids extracted from each symptomatic plant
with reverse transcription (RT)-PCR. The samples (n = 26) gave an RT-PCR product of the expected size with the group-specific potyvirus RT-PCR test. One sample was positive with the carlavirus group RT-PCR test.

RT-PCR products from both tests were cloned and sequenced. Comparisons with sequences in GenBank showed that all but one had Onion yellow dwarf virus (OYDV), whereas one sample had a mixed infection of OYDV and Leek yellow stripe virus. Sequence analysis showed that the carlavirus was Garlic common latent virus. Sequence
identities ranged from 95-99 percent for each of the viruses when compared with those available in GenBank. All samples were then tested for each of these viruses with commercially available antisera. Results of ELISA confirmed the findings of RT-PCR.

To our knowledge, this is the 1st report for each of these garlic viruses from Washington State. This finding prompts the need for evaluating all garlic accessions for the potential impact of these viruses on garlic germ plasm conservation and distribution.

References:
(1) L. J. du Toit et al. Plant Dis. 88:222, 2004.
(2) R. M. Hannan and E. J. Sorensen. Crop Profile for Garlic in Washington. Washington State University Coop Extension and the U.S. Department of Agriculture, 2002.
(3) S. S. Pappu et al. J. Virol. Methods 41:9, 1993.

[OYDV is transmitted by _Myzus persicae_ and other aphid species, or mechanically to onions and other crops such as garlic, leek and some narcissus species. It is not spread by seed, but infected bulbs (transplants and volunteers) always produce diseased plants and serve as a source of contamination for following seasons, especially when aphid populations are high. Disease management relies on use of disease-free transplants and crop rotation out of onion production for at least 3 years. Other disease management recommendations include isolation from other susceptible crops or volunteer [self-sown] onions. Insecticides may suppress vector populations but generally are not necessary or effective.

Garlic common latent carlavirus is of minor significance, but combined with other viruses can cause severe disease in Europe, South and Central America, India and China. Leek yellow stripe potyvirus causes severe disease in autumn and winter leek crops in western Europe and is probably present in leek production areas worldwide.

Links: <http://highplainsipm.org/HpIPMSearch/Docs/YellowDwarf-Onion.htm> - Mod.DH]