Tomato leaf curl New Delhi virus (ToLCNDV) is an emerging begomovirus (
family) listed in the EPPO Alert List 2, present in the Mediterranean area and in Italy, where it was reported in 2015 in ...Sicilian courgette. The virus is widespread in cucurbits where it causes up to 100% production losses. In 2018, ToLCNDV was isolated in Apulia (southern Italy) in commercial fields of zucchini squash and since then its recurrent outbreaks generated justified concern among growers. Thus, a sustainable and environmentally friendly approach must be adopted. Genetic resistances have been identified in
and
but, compared to genetic resistance, grafting could provide a faster and more flexible solution because the graft wounding induces tolerance rather than resistance against airborne virus infection. Compared to tolerance, the up-regulation of resistance genes requires energy resources mobilized at the expense of primary metabolism, plant growth, and development. Results of screening among twenty-one local cucurbit cvs. ecotypes and accessions to evaluate tolerance levels against rub-inoculation of ToLCNDV led to the identification of potential rootstocks to attain suitable levels of tolerance against the virus in commercial cucurbit varieties. Cucurbit plants were challenged by a ToLCNDV isolated in Apulia denoted ToLCNDV-Le and evaluated for disease symptoms development and viral DNA accumulation up to 28 days after inoculation. On the basis of disease symptoms developed, plants were classified as tolerant, moderately tolerant, moderately susceptible, and susceptible.
cv. Barattiere did not show any detectable disease symptoms and very low levels of viral DNA accumulation was recorded; thus, it was used as rootstock for some of the remaining cucurbit genotypes that were used as scions. The tolerance trait was transmitted to the otherwise susceptible and moderately susceptible cucurbit genotypes grafted onto the cv. Barattiere. The results of this study suggest practical implications of the approach described.
Summary
Many weeds that are closely associated with horticultural activities are known as natural reservoirs of plant viruses. However, whether these weeds can also serve as hosts of pospiviroids is ...not well known. Pospiviroids are naked, non‐coding RNA pathogens that cause severe economic damage in many solanaceous crops. In this study, we examined the overall risk of pospiviroid spreading from weeds to economically important crops, by combining the results from previous inoculation studies with new results coming from a survey, a contact experiment and an inoculation experiment. A survey of commercial ornamental glasshouses revealed that ornamental plants mainly belonging to the Solanaceae harbour pospiviroids, in contrast to weed species sampled in the same places. No new weed hosts could be identified after testing weeds that grew in contact with Tomato apical stunt viroid (TASVd)‐infected plants of tomato (Solanum lycopersicum) and jasmine nightshade (Solanum jasminoides) in an experimental glasshouse. Finally, in mechanical inoculation experiments with TASVd, none of the six tested weed species were determined to be a host at 6 weeks after inoculation. Commonly occurring weed species therefore do not appear to play a significant role as reservoir hosts for pospiviroids. This does not rule out other potential weed hosts that have not yet been tested. Inoculation studies should include rigorous experimental protocols with a sufficient number of replicated as well as adequate positive controls. The information gained through this study may prove useful in future risk assessments for the pospiviroid group.
Viroids are noncoding RNA pathogens inducing severe to mild disease symptoms on agriculturally important crop plants. Viroid replication is entirely dependent on host transcription machinery, and ...their replication/accumulation in the infected cells can activate RNA silencing-a host defense mechanism that targets the viroid itself. RNA silencing produces in the cell large amounts of viroid-specific small RNAs of 21-24-nucleotides by cleaving (or "dicing") entire molecules of viroid RNA. However, viroid replication is resistant to the effects of RNA silencing and disrupts the normal regulation of host gene expression, finally resulting in the development of disease symptoms on infected plant. The molecular mechanisms of biological processes involving RNA silencing and underlying various aspects of viroid-host interaction, such as symptom expression, are of special interests to both basic and applied areas of viroid research. Here we present a method to create infectious viroid cDNA clones and RNA transcripts, the starting material for such analyses, using Hop stunt viroid as an example. Next we describe methods for the preparation and analysis of viroid-specific small RNAs by deep sequencing using tomato plants infected with Potato spindle tuber viroid as an example. Finally we introduce bioinformatics tools and methods necessary to process, analyze, and characterize these viroid-specific small RNAs. These bioinformatic methods provide a powerful new tool for the detection and discovery of both known and new viroid species.
Plant viruses cause many of the most important diseases threatening crops worldwide. Over the last quarter of a century, an increasing number of plant viruses have emerged in various parts of the ...world, especially in the tropics and subtropics. As is generally observed for plant viruses, most of the emerging viruses are transmitted horizontally by biological vectors, mainly insects. Reverse genetics using infectious clones—available for many plant viruses—has been used for identification of viral determinants involved in virus–host and virus–vector interactions. Although many studies have identified a number of factors involved in disease development and transmission, the precise mechanisms are unknown for most of the virus–plant–vector combinations. In most cases, the diverse outcomes resulting from virus–virus interactions are poorly understood. Although significant advances have been made towards understand the mechanisms involved in plant resistance to viruses, we are far from being able to apply this knowledge to protect cultivated plants from the all viral threats.The aim of this Special Issue was to provide a platform for researchers interested in plant virology to share their recent results. To achieve this, we invited the plant virology community to submit research articles, short communications and reviews related to the various aspects of plant virology: ecology, virus–plant host interactions, virus–vector interactions, virus–virus interactions, and control strategies. This issue contains some of the best current research in plant virology.
Inoculation of mild virus strain prior to severe virus strain to protect plant against viral disease is the principle of cross protection. Five mild strains of Chili veinal mottle virus (ChiVMV), ...i.e. -KAR, -SPR, -SKT, -CSR, and -PGL were used as cross protection agent to protect chili pepper plants against severe strain infection of ChiVMV-CKB. The mild strains were inoculated mechanically prior inoculation of severe strain and the efficiency of cross protection was evaluated by observing symptom development and measuring crop yield. Inoculation of mild strains 7 days prior inoculation of severe stain was not able to protect the plant from infection of severe strain ChiVMV-CKB. Protective effect was observed when mild strains were inoculated at 14, 21, and 28 days prior inoculation of severe strain. Symptom development was suppressed or delayed, and crop yield was not significantly different with healthy plants. It was suggested that to obtain the best protection against severe strain, the mild strain should be applied as early as possible before the occurrence of severe strain infection.
Watermelon mosaic virus(WMV) is one of the major viruses infecting cucurbit crops worldwide. Although WMV is very common worldwide,little is known about the biological traits of WMV isolates from ...China. Hence, this study aimed to characterize 11 WMV isolates infecting melon from different geographical origins in Xinjiang based on experimental hosts. Sap inoculation of the 11 WMV isolates onto a range of 13 plant species revealed some differences compared to the WMV isolates collected from other countries. Our results showed that, overall, there were no obvious correlations of host responses to inoculation with WMV isolates from different geographical origins. However, isolate JS-1 caused mild mosaic on Cucurbita moschata, whereas the remaining 10 isolates were asymptomatic on this plant species. Moreover, in Datura stramonium, isolate TYG-1 induced mosaic, whereas the remaining 10 isolates did not infect this species. All isolates infected systemically Cucurbita pepo and Cucumis melo plants, causing severe symptoms. All isolates did not induce any symptoms on Cucumis sativus, but the virus could be detected using RT-PCR. Additionally, all isolates infected systemically Nicotiana tabacum plants, causing mild mosaics. Chenopodium amaranticolor and Chenopodium quinoa reacted to all isolates by chlorotic local lesions in the inoculated leaves, and the virus was detected in the inoculated leaves using RT-PCR. In addition, the attempts to transmit the isolates to Luffa cylindrica, Vicia faba, Phaseolus vulgaris, Vigna unguiculata or Pisum sativum failed as confirmed by negative RT-PCR. Our results would be useful for understanding the biological variability of WMV.
Sixty-nine tomato genotypes representing nine
Solanum
species were evaluated for resistance to
Cucumber mosaic virus
(CMV) subgroup IA and its aphid vector
Myzus persicae
. Resistance was assessed by ...visual scoring of symptoms in the field under natural conditions, and in the greenhouse by artificial inoculations through aphid
M. persicae
and mechanical transmissions in the year 2007 and 2009. Considerable variation in responses was observed among the evaluation methods used. Field evaluations were found liable to errors as different levels were observed for the same genotypes in the different years, however mechanical inoculation was found to be the most useful in identifying CMV subgroup IA resistance, in contrast aphid transmission was most useful in identifying insect transmission resistance. All genotypes observed as highly resistant to CMV subgroup IA in the field or through vector transmission became systemically infected through mechanical inoculations. Using mechanical inoculation, six genotypes (TMS-1 of
S. lycopersicum
, LA1963 and L06049 of
S. chilense
, LA1353, L06145 and L06223 of
S. habrochaites
) were found resistant and another six (L06188 and L06238 of
S. neorickii
, L06219 of
S. habrochaites
, L05763, L05776 and L06240 of
S. pennellii
) were found tolerant showing mild symptoms with severity index (SI) ranging 1-2 and with delayed disease development after a latent period (LP) of 18–30 days. However, these genotypes were found to be resistant to highly resistant in the field and through inoculation by
M. persicae
; and they also supported low population levels of
M. persicae
except TMS-1. Another nine genotypes (LA2184 of S
. pimpinellifolium
L., LA2727 of
S. neorickii
, LA0111, L06221, L06127 and L06231 of S
. peruvianum
L., LA1306, L06057 and L06208 of
S. chmielewskii
) showing a susceptible response after mechanical inoculation were highly resistant, resistant and tolerant after
M. persicae
transmission. The resistant genotypes, identified in the present study can be exploited in the breeding programmes aimed at developing tomato varieties resistant to CMV subgroup IA and broadening the genetic base of CMV-resistant germplasm. The differences observed between mechanical and aphid transmission suggests that one should consider both evaluation methods for tomato germplasm screening against CMV subgroup IA.
The objective of present study was symptomatic and molecular characterization of the virus that infects Carica papaya L. in areas of northern Peru. To do this, of different fields were collected ...leaves of C. papaya with mosaic symptoms, chlorosis and distortion the leaf. Sap of these leaves was inoculated mechanically onto virus-free plants of C. papaya, Chenopodium murale, Ch. amaranticolor, Ch. quinoa, Cucumis melo, C. sativus and Cucurbita pepo; which they were kept at room temperature for 45 days, after which young leaves in of C. papaya, mosaic, distortion and reduction of the leaf blade was observed; in the species C. melo, C. sativus and Cucurbita pepo systemic chlorosis. Ch. murale, Ch. amaranticolor and Ch. quinoa they no showed symptoms evident. The plants infected were analyzed by serological technique NCM-ELISA and RT-PCR proving that the virus that is infecting the plantations assessed in the north of Peru, it is the papaya ringspot virus (RSVP). DOI: 10.17268/sci.agropecu.2015.04.01
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