Identification and characterization of a new potyvirus infecting cucurbits

A new potyvirus, tentatively named cucurbit vein banding virus (CVBV), was identified in crops of cucurbits in San Pedro (Buenos Aires, Argentina). The complete genome sequences of two isolates of CVBV were obtained by next-generation sequencing (Illumina). The genomic RNA consisted of 9968 and 9813 nucleotides, respectively, and displayed typical potyvirus organization. The percentage identity for these two genome sequences, using BLASTn, was 77% to sweet potato virus c and 73% to tomato necrotic stunt virus. BLASTx analysis of the complete polyprotein showed that the most closely related virus is plum pox virus, with 48% amino acid sequence identity for both isolates. Sequence comparisons and phylogenetic analyses indicate that CVBV belongs to a previously undescribed species in genus Potyvirus.

Detection and identification of a novel 16SrXIII subgroup phytoplasma associated with strawberry red leaf disease in Argentina

Strawberry red leaf phytoplasma was found in strawberry plants from production fields in Lules (Tucumán province) and Bella Vista (Corrientes province), Argentina. Characteristic strawberry red leaf symptoms were stunting, young leaves with yellowing at the edges, mature leaves which curled and were reddish at the abaxial face, flower and fruit deformation and death. The pathogen was detected with phytoplasma-universal primer pairs P1/P7 followed by R16F2n/R16R2 as nested primers in 13 diseased plants. Based on RFLP and sequence analysis of the amplified 16S rRNA gene, the phytoplasma was related to the 16SrXIII group (Mexican periwinkle virescence). In silico the RFLP profile of all the samples analysed revealed the presence of a unique pattern, showing that the novel phytoplasma is different from all the phytoplasmas currently composing the 16SrXIII group. The phylogenetic analysis was consistent with RFLP analysis as the strawberry red leaf phytoplasma was grouped within the 16SrXIII group, but formed a particular cluster. On this basis, the Strawberry red leaf phytoplasma associated with strawberry red leaf disease was assigned to a new subgroup, 16SrXIII-F.

Detection and identification of the first viruses in chia (Salvia hispanica)

Chia (Salvia hispanica), an herbaceous plant native to Latin America, has become important in the last 20 years due to its beneficial effects on health. Here, we present the first record and identification of two viruses in chia plants. The comparison of the complete nucleotide sequences showed the presence of two viral species with the typical genome organization of bipartite New World begomovirus, identified as Sida mosaic Bolivia virus 2 and Tomato yellow spot virus, according to the ICTV taxonomic criteria for begomovirus classification. DNA-A from Sida mosaic Bolivia virus 2 exhibited 96.1% nucleotide identity with a Bolivian isolate of Sida micrantha, and Tomato yellow spot virus showed 95.3% nucleotide identity with an Argentine bean isolate. This is the first report of begomoviruses infecting chia as well as of the occurrence of Sida mosaic Bolivia virus 2 in Argentina.

Striking differences in the biological and molecular properties of onion and garlic isolates of onion yellow dwarf virus

Complete nucleotide (nt) and deduced amino acid sequences of two onion yellow dwarf virus (OYDV) isolates showing mild and severe symptoms in onion but being unable to infect garlic were determined. The genomes consisted of 10,459 and 10,461 nt (without the 3' poly(A) tail) and were 92.2 % identical. Comparison of their whole genomes, polyproteins and P1, HC-Pro, P3, CI, VPg and NIa-Pro regions with those of garlic isolates previously identified as OYDV gave percentage values below that proposed as the molecular threshold for potyvirus species demarcation. This and the striking differences in host range between onion and garlic isolates suggest that they represent different virus species.

First Report of Shallot latent virus in Garlic in Argentina

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.

Yield Loss in Garlic Caused by Leek yellow stripe virus Argentinean Isolate

Garlic plants (Allium sativum) are naturally infected by a complex of viruses in the genera Potyvirus, Carlavirus, and Allexivirus. The yield of virus-free garlic plants (noninoculated control) was compared with that of plants infected with an Argentinean isolate of Leek yellow stripe virus (LYSV; L treatment) and garlic plants infected with the virus complex (VC). Evaluations were conducted in the field and in anti-aphid cages during two crop cycles after planting three sizes of cloves (categories). The percent plant emergence in the noninoculated control and in the L treatments (between 80 and 100%) did not differ statistically, but the percent emergence for these two treatments was double that for the VC treatment (25 to 62%). Plant height and leaf number in the L treatment were lower than in the noninoculated control during the first evaluation (year 1), but they did not differ during the second evaluation (year 2). However, both treatments produced taller plants with more leaves than those of VC in both years. The L treatment decreased bulb weight up to 28% and perimeter up to 9% when compared with those in the noninoculated control maintained in the anti-aphid cages until the end of the experiment. However, differences between these treatments were higher in the field experiments where plants were exposed to infection by other viruses (up to 36% in bulb weight and 13% in perimeter). Bulbs of the VC-infected plant treatment were reduced up to 74% in weight and 37% in perimeter. In field evaluations, a high percentage of plants were infected with Onion yellow dwarf virus (58 to 100%), whereas fewer were infected with LYSV (15 to 68%). Garlic virus A infection was high in plants previously infected with LYSV (96 and 97%), but lower in the noninoculated control (12 and 68%). These results show the high impact of the virus complex on garlic yield and the effect of LYSV as a component of the garlic virus complex.

Changes in the Concentration of an Allexivirus During the Crop Cycle of Two Garlic Cultivars

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.

Effect of Two Allexivirus Isolates on Garlic Yield

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 Associated with Virus-Infected Garlic Plants During Five Successive Years

Virus-free garlic plants, when planted in the field, are quickly infected by viruses, but it is not known to what extent this affects the yield over successive crop cycles. The yield loss curve was studied for these plants during 5 years of tests in the field. Highly significant differences were detected in the weight and perimeter of bulbs in relation to the years of exposure to virus infection. An increase was observed in yield compared with chronically diseased plants of between 66 and 216% in weight and 13 and 37% in perimeter of bulbs in the first crop cycle and 49% in weight and 16% in perimeter in the fifth year. These results showed a gradual loss in yield until the third year, and subsequently the production values remained steady for the fourth and fifth years of testing but were still higher than those reached by chronically diseased plants.

Variations of Leek yellow stripe virus Concentration in Garlic and Its Incidence in Argentina

The purpose of this work was to determine variations in titer of Leek yellow stripe virus (LYSV) throughout the crop cycle and bulb storage, and to evaluate the incidence of infected plants in the main garlic-production regions of Argentina. One hundred plants with LYSV from each of five cultivars were analyzed by double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) in six different vegetative stages in White- and Red-type garlic cultivars and seven stages in cv. Rosado Paraguayo, throughout the year. In two White-type garlic cultivars, LYSV showed peaks of viral concentration in May, at the beginning of the crop cycle, and in November, just before harvest. In two Red-type garlic selections, an increase was detected in November (period of bulbing). The highest virus titers for these four garlic cultivars were detected in devernalized clove. In Rosado Paraguayo, the peak virus concentration occurred in September prior to harvesting. In a survey at 14 different localities in Argentina, 3,066 random samples were analyzed. LYSV was found in 80 to 98% of the plants from all regions, except in Santa Cruz, where 34% of plants were infected. The importance of this study is that it allows us to recommend the most suitable moment of the year to make the analysis with DAS-ELISA.