Garlic (Allium sativum) is infected by numerous viruses forming a viral-complex, which is widely distributed in the garlic production regions of Argentina. This work is the first report of the effect of two Allexivirus isolates, Garlic virus A (GarV-A) and Garlic virus C (GarV-C), on garlic yield. Garlic cvs. Morado-INTA and Blanco-IFFIVE were used in the experiments, and four treatments were evaluated: plants inoculated with GarV-A only, GarV-C only, virus-free plants (negative control), and plants infected with the virus-complex. Assays were performed in anti-aphid cages and in the field during 2002 and 2003. GarV-A caused significant reductions in bulb weight (14 to 32%) and diameter (6 to 11%) compared with the negative control in the two cultivars under both assay conditions. GarV-C caused less damage than GarV-A (15% in weight and 5% in diameter) with respect to the negative control in cv. Blanco-IFFIVE, and did not produce significant yield losses in cv. Morado-INTA in either year or under either assay condition.

Yield losses caused by a second viral infection of garlic plants previously infected with either of the isolated Allexiviruses, Garlic virus-A

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Garlic can be infected by a number of viruses, including allexiviruses. The coat protein sequence of an Allexivirus was detected in Argentina and deposited in the EMBL database as Garlic mite-borne filamentous virus (accession number X98991); it has high homology with Garlic virus A (GarV-A). For reliable virus detection, plants should be sampled when virus titer is high to reduce the risk of identifying infected plants as healthy. The objective of this study was to describe fluctuations in the concentration of this Argentine isolate of GarV-A in two garlic cultivars, Morado-INTA and Nieve-INTA, throughout the crop cycle using the double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). Over a 2-year period, for both cultivars, virus concentration was assessed in samples from the tips section of the youngest leaves of GarV-A-infected plants, and from basal sections of both dormant and devernalized cloves of stored bulbs of Morado-INTA. The concentration of GarV-A varied during the crop cycle, but peaked at the beginning and again at the end of the crop cycle. Virus concentration was slightly higher in devernalized cloves compared with dormant cloves of Morado-INTA. No correlation between virus concentration and mean air temperature was observed. The results of this study recommend sampling times at the beginning of the crop cycle at 64 to 81 days after planting, and towards the end of the crop cycle to evaluate for the presence of GarV-A by DAS-ELISA.

Because of exclusively agamic propagation, garlic is commonly infected with a virus complex mainly composed of species within the genera Potyvirus, Allexivirus, and Carlavirus. This virus complex causes leaf striping that ranges from various shades of green to yellow and results in yield losses (2,4). Onion yellow dwarf virus, Leek yellow stripe virus (potyviruses), Garlic virus A, Garlic virus C (allexiviruses), and Garlic common latent virus (carlavirus) have been detected in Argentina previously (1,2). Recently, Shallot latent virus (SLV; another carlavirus) was detected in 25 of 30 garlic plants (cv. Morado) growing in four different fields near Córdoba, Argentina by double-antibody sandwich (DAS)-ELISA using BIOREBA (Reinach, Switzerland) antibodies. To confirm the presence of the virus, DAS-ELISA-positive plants were also analyzed by one-step reverse transcription (RT)-PCR using the Access RT-PCR system (Promega, Madison, WI) with specific primers reported by Tsuneyoshi et al. (3). RNA extractions were performed from 100 mg of leaves with the Qiagen RNeasy Plant Mini Kit (Qiagen, Valencia, CA). Primers used were Car-V1 (5′-AAACCTTTTGGTTCACTTTAGG-3′); Car-V2 (5′-AGGTGCATTGTTATCATTACTGG-3′); and Car-Cp3 (5′-GCGTGCTATATTTAAGTTGCATAC-3′). Primer pairs Car-V1/Car-Cp3 and Car-V2/Car-Cp3 were used for the amplification of the coat protein (CP) gene of SLV and an isolate of SLV formerly known as Garlic latent virus, respectively. Fragments of 992 bp and 1,079 bp were amplified with these primer pairs, respectively. The RT-PCR products were cloned with the TOPO TA Cloning Kit in the 3.9-kb pCR-TOPO vector (Qiagen). The nucleotide sequences of both fragments were determined and were found to be identical (GenBank No. GU355922) showing 94.2% nt sequence identity with the CP gene of an isolate of SLV from Indonesian garlic (GenBank No. AB004686) formerly referred to as Garlic latent virus (3). Consequently, the Argentinean virus is now considered a garlic isolate of SLV. References: (1) E. Cafrune et al. Plant Dis. 90:898, 2006. (2) V. C. Conci. Virus y Fitoplasmas de Ajo. Page 267 in: 50 Temas Sobre Producción de Ajo. Vol. 3. J. L. Burba, ed. Ediciones INTA, Mendoza, Argentina. 1997. (3) T. Tsuneyoshi et al. Arch. Virol. 143:1093, 1998. (4) D. G. A. Walkey and D. N. Antill. J. Hortic. Sci. 64:53, 1989.

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