Viral complexes in the Allium cepa L.- Frankliniella occidentalis P. interaction by DAS-ELISA in Baja California, Mexico

The onion (Allium cepa L.) is one of the main horticultural crops produced in Baja California, Mexico. In this crop, it has been observed presumptive viral symptoms, which are able to cause losses in yield and quality. Therefore, the objective of this study was to detect the associated virus in onion in high producing culture zones in Baja California. Plant material samples (symptomatic and asymptomatic) and trips insects were collected from commercial farming or areas. Commercial anti-serum were used for the detection of Iris yellow spot virus (IYSV), Tomato spot wilt virus (TSWV), Leek yellow spot virus (LYSV), Onion yellow dwarf virus (OYDV) and Garlic common latent virus (GarCLV). Seven indicator plants species were mechanically inoculated with onion sap (symptomatic and asymptomatic). The results showed the presence of IYSV, TSWV, OYDV and GarCLV in symptomatic onion plants. The plant samples showed a 77 % of incidence in the form of viral complexes and in a 23 % only the presence of LYSV was detected. The trips identified as Frankiniella occidentalis P. harbored IYSV, TSWV, LYSV, OYDV and GarCLV in the form of complexes in La Trinidad and San Quintin. The indicator plants did not show sympotoms of virosis. It is evident that F. occidentalis P. is responsible for the transmision of the analyzed viruses in this study in cultured onions. There are not previous reports for the detection of Orthotospovirus, Potyvirus and Carlavirus in Baja California onions.

Double Infection of Onion yellow dwarf virus and Shallot latent virus in Garlic from Several Regions in Indonesia

Viruses have been a problem on garlic cultivations in various countries. There are several viruses reported infecting garlic. Genera Potyvirus and Carlavirus are the most common viruses found infecting garlic. Mixed infection on garlic is often designated as a “garlic viral complex”. These viruses can be transmitted through imported garlic seeds. Therefore, it is necessary to conduct early detection of garlic seeds to prevent the epidemic of these viruses. This study aimed to detect Onion yellow dwarf virus (OYDV) and Shallot latent virus (SLV) on garlic. Garlic samples were obtained from Enrekang, Magelang, Temanggung, Tawangmangu, and Yogyakarta. Total RNA was extracted from the samples and subsequently used for RT-PCR using two pairs of specific primers SLV-F/SLV-R and OYDV-F/OYDV-R. Primary pair SLV-F/SLV-R in amplicons sized 276 bp, while OYDV-F/OYDV-R in amplicons sized 112 bp. RT-PCR results showed that OYDV was found in all samples tested in this study. Meanwhile, double infections (OYDV and SLV) were found in eight out of ten samples tested. These results indicated that double infections on garlic were common in Indonesia.

Detection and Distribution of Viruses Infecting Garlic Crops in Australia

The distribution of viruses in eastern Australian field garlic was evaluated. Detection assays were developed that involved generic RT-PCR for viruses in the Allexivirus, Carlavirus and Potyvirus genera followed by virus-specific colorimetric dot-blot hybridization. Assays targeted the potyviruses (onion yellow dwarf virus (OYDV), shallot yellow stripe virus (SYSV), and leek yellow stripe virus (LYSV)), the carlaviruses (garlic common latent virus (GCLV) and shallot latent virus (SLV)), and the allexiviruses (garlic viruses A, B, C, X (GarVA, -B, -C, -X) and shallot virus X (ShVX)). Virus incidence in crops was consistently high, with most plants infected with at least one virus from each genus. OYDV, LYSV, SLV, and GCLV were commonly detected. Three of the four allexiviruses were in all districts surveyed but varied in incidence, whereas ShVX and SYSV were not detected. There was no association between virus species complement and bulb size, indicating size is not a good predictor of the virus status of planting material. The variation of virus incidence across different Australian growing districts and in different cultivars implies multiple introductions of viruses rather than spread within the country. The genetic diversity observed within coat protein sequences of some virus species also supports multiple separate introductions.

Characterization of Volatile Organic Compounds in ‘Rossa di Tropea’ Onion by Means of Headspace Solid-Phase Microextraction Gas Chromatography–Mass Spectrometry (HS/SPME GC–MS) and Sensory Analysis

Background: Plant viral infections induce changes in the host plant, which can potentially impact composition, organoleptic properties, and storability characteristics of plant products. In particular, onion odor and flavor are determined mainly by volatile organic compounds, and changes upon infection with onion yellow dwarf virus may deeply influence these characters. Methods: A time-course study of volatile organic compounds in onion yellow dwarf virus-infected versus healthy ‘Rossa di Tropea’ onion bulbs was performed using headspace solid-phase microextraction gas chromatography–mass spectrometry; sensory analysis performed at marketability stage of onion production was used to correlate such changes to the taste characteristics perceived by consumers. Results: Volatile organic compounds regulated in infection conditions were identified, mainly belonging to mono- and poly-sulfides classes. The most abundant compounds in the analyzed samples were propyl disulfide, allyl-isopropyl disulfide, and propanethiol; significantly different concentrations were observed for 7 out of 11 VOCs in virus-infected compared to healthy bulbs. Statistical analysis based on a partial least squares discriminant analysis model and hierarchical cluster analysis allowed us to cluster samples based on phytosanitary status and storage time and to identify the most responsible compounds for such classification. Conclusions: Onion yellow dwarf virus infection induces changes in volatile organic compounds in onion during storage. The impact of such regulated compounds on ‘Rossa di Tropea’ onion odor and flavor and correlation with sensory analysis are discussed.

Production of Virus-Free Garlic Plants through Somatic Embryogenesis

The present study was conducted to establish a protocol for the regeneration of virus-free garlic plants through somatic embryogenesis of two Croatian garlic ecotypes. Basal parts of cloves from mother plants were cultured on a full Murashige and Skoog (MS) or modified MS medium (¼ of KNO3 and NH4NO3 and 2xMgSO4) containing 0.1 mg L−1 2,4-dichlorophenoxyacetic acid (2,4-D) or 1 mg L−1 2,4-D + 0.5 mg L−1 kinetin (Kin) and representing four different treatments. Plants were regenerated in MS medium containing 0.1 mg L−1 2,4-D and rooted in a medium containing 0.05 mg L−1 1-naphthaleneacetic acid (NAA) + 0.005 mg L−1 6-(γ,γ-dimethylallylamino)purine (2iP). The presence of viruses (i.e., sanitary status) of the mother plants and regenerants was checked by enzyme-linked immunosorbent assay (ELISA) and reverse transcription-polymerase chain reaction (RT-PCR). The mother plants were infected with onion yellow dwarf virus (OYDV) and leek yellow stripe virus (LYSV). In addition, the presence of garlic common latent virus (GCLV) was confirmed in four mother plants. Embryogenic callus developed in all four treatments with success ranging from 55% to 81% depending on treatment and ecotype. Plant conversion was significantly higher in somatic embryos developed in media containing 0.1 mg L−1 2,4-D than those developed in media containing 1 mg L−1 2,4-D + 0.5 mg L−1 Kin. Virus elimination success ranged from 13.3% up to 62.5% depending on garlic ecotype and treatment. The overall rate of virus elimination by somatic embryogenesis for both treatments and ecotypes were 20.7%, 22.9%, and 30.5% for OYDV, GCLV, and LYSV, respectively. Based on these results, somatic embryogenesis has been shown to be equally or more successful in eliminating garlic viruses compared to other in vitro methods.

Identification and molecular characterization of onion yellow dwarf virus (OYDV) in Allium cepa crops in Poland

Onion yellow dwarf virus is distributed worldwide significantly reducing yield of crops from the Allium genus. The aim of the study was the detection and molecular characterization of newly identified OYDV isolates infecting onions in Poland. The virus was detected by transmission electron microscopy and RT-PCR techniques using two pairs of diagnostic primers: OYDV-NibCPF1/R1 and OYDV-CPF2/R2. The specificity of obtained RT-PCR products was confirmed by Sanger sequencing and received viral coat protein sequence was used for phylogenetic analysis. The phylogenetic analysis was carried out using CP sequences of the new Polish onion isolate obtained in this study and 37 other sequences of OYDV retrieved from GenBank. The analysis revealed that the Polish OYDV isolate is the most similar to the OYDV isolates derived from onions from Argentina and Germany, which may indicate their common origin. Moreover, it was observed that the Polish onion and garlic isolates are very diverse and belong to different phylogroups.