Papaya Ringspot Virus Research Articles

Evaluation of various selections on growth, flowering, yield and quality in papaya

An experiment was conducted to evaluate the different selections along with Pusa Dwarf as a check for growth, flowering, yield and quality traits in papaya. The experiment was conducted at Fruit Research Station, Madhadi bag farm, Department of Horticulture, College of Agriculture, JAU, Junagadh (Gujarat). The study revealed that the maximum number of fruits per plants (36.38) and fruit yield (33.81 kg/pl. & 84.52 ton/ha) were noted in Selection-4 (GJP-1). The bearing height is good shine and the check vareity Pusa Dwarf performed with lowest bearing height, but was found at par with Selection-4 (GJP-1). Variation in growth parameters was found significant and lowest plant height and maximum number of leaves/plant were recorded in Pusa Dwarf, while, highest stem girth was noted in Selection-6, but they were observed at par with Selection-4 (GJP-1). Flowering is the main object of plant to target the yield. Significantly the lowest days to flowering was noted in Selection-1 but maturity in Selection-4 (GJP-1). Maximum number of female flower /node was registered in Selection-3, whereas, highest length of pistilate flower, staminate flower and male flower stalk were noted in Selection-6, however, all were found at par with Selection-4(GJP-1). Among the various physical parameters studied, highest fruit length & weight (25.02 cm & 1832 g) were noted in Selection-6, whereas, highest fruit girth (47.3 cm) was noted in Pusa Dwarf but was observed at par with Selection-4 (GJP-1). It was also performed better for highest pulp weight (1327.93 g) and pulp seed ratio (1230.56). Likewise, highest pulp-peel ratio (5.74) was noted in Selection-8, but lowest peel weight (166.10 g) and seed weight (63.63 g) were registered in Selection-2 & 7. In the present study, Selection-6 & 4 (GJP-1) established its supremacy in quality parameters viz., TSS, total sugars, reducing sugar, non-reducing sugar over the other varieties. The organolaptic parameters have also great significant to judge the prefarability of the vareity. Highest score of pulp color and taste were noted in Selection-6 & 5, respectively, whereas, the highest flavor, texture and over all acceptibility were registerd in Selection-2, however, it was found at par with Selection-4 (GJP-1). Fruit firmness and shelf life of the fruit is also an important feature which enhances the more market price for longer period due to good keeping quality. Highest fruit firmness and shelf life were noted in Selection-7. Papaya Ring Spot Virus (PRSV) is the major devastating disease of papaya. The result was also observed significant and lowest PRSV infestation was noted in Selection-4 (GJP-1).

Genetic diversity and biological characterization of watermelon mosaic virus isolates from Iran and Iraq.

No abstract Keywords: genetic diversity; Iran and Iraq; water melon; mosaic virus; cucurbits.

Detection of Cucurbit Yellow Stunting Disorder Virus Infecting Watermelon in South Carolina

Watermelon is an important cucurbit crop grown in 44 states in the United States of America (USA). South Carolina (SC) had the seventh largest watermelon production area in USA with 4,500 acres in 2018 valued at approximately $17 million. In June 2019, four watermelon plants displaying symptoms of virus infection including stunting, leaf crumpling, interveinal chlorosis, and necrosis of leaf margins were observed in a research trial in Charleston, SC. Whiteflies were observed on the abaxial surface of the leaves. One plant was tested for the presence of whitefly-transmitted cucurbit leaf crumple virus (CuLCrV), cucurbit yellow stunting disorder virus (CYSDV), and squash vein yellowing virus and aphid-transmitted papaya ringspot virus by RT-PCR. Amplicons of the expected size were only observed for CuLCrV (∼1 kb) and CYSDV (∼0.7 kb). Because CYSDV was not previously reported from SC, we continued to monitor the field for virus symptoms during the summer season. By mid-August 2019, 15 additional plants (1.9% incidence) were observed with similar symptoms of virus infection. Two virus identification methods (CP and Hsp70h) confirmed that CYSDV was indeed present in watermelon samples in SC. The geographic range of CYSDV and other whitefly-transmitted viruses continues to expand into and within major cucurbit-producing regions with each production season, especially in the southeastern USA. This is the first report of CYSDV infecting watermelon or any other plant in SC. These three whitefly-transmitted viruses now need to be considered in management plans by SC growers. Knowledge of the presence of CYSDV, an additional virus, infecting cucurbits, in SC is also important from a regulatory perspective.

Correlation of Leaf Parameters with Incidence of Papaya Ring Spot Virus in Cultivated Papaya and its Wild Relatives

Papaya ring spot virus (PRSV) disease has been the major impediment in papaya cultivation. The disease is transmitted through three aphid vectors and field tolerance towards this disease varies among Carica papaya cultivars as well as within the Vasconcellea genus. Leaf morphological traits are known to have influence on the probing preferences of aphids. Hence, this study was conducted to know whether the leaf parameters could contribute to the incidence of PRSV possibly by influencing the probing or feeding behaviour of aphid vectors. Leaf parameters viz., leaf thickness, leaf epicuticular wax content, presence and type of trichomes, trichome density were correlated with disease incidence at field conditions. The result revealed that leaf thickness along with epicuticular wax content had significant negative correlation with disease incidence. Similarly, trichome density had negative impact on disease incidence at 99.92% significance level. High epicuticular wax content and high trichome density in V. cauliflora and V. cundinamarcensis were found to be negatively associated with low to very low infection indicating that these parameters may have limited the vector transmission significantly.

Correlation of Leaf Parameters with Incidence of Papaya Ring Spot Virus in Cultivated Papaya and its Wild Relatives

Papaya ring spot virus (PRSV) disease has been the major impediment in papaya cultivation. The disease is transmitted through three aphid vectors and field tolerance towards this disease varies among Carica papaya cultivars as well as within the Vasconcellea genus. Leaf morphological traits are known to have influence on the probing preferences of aphids. Hence, this study was conducted to know whether the leaf parameters could contribute to the incidence of PRSV possibly by influencing the probing or feeding behaviour of aphid vectors. Leaf parameters viz., leaf thickness, leaf epicuticular wax content, presence and type of trichomes, trichome density were correlated with disease incidence at field conditions. The result revealed that leaf thickness along with epicuticular wax content had significant negative correlation with disease incidence. Similarly, trichome density had negative impact on disease incidence at 99.92% significance level. High epicuticular wax content and high trichome density in V. cauliflora and V. cundinamarcensis were found to be negatively associated with low to very low infection indicating that these parameters may have limited the vector transmission significantly.

First Report of Natural Infection of Siraitia grosvenorii by Cucumber Green Mottle Mosaic Virus in China

Fruit of Siraitia grosvenorii (family Cucurbitaceae) are used as a sweetener in beverage and traditional herbal medicine production in China. Some viruses have been known to infect S. grosvenorii, such as papaya ringspot virus (PRSV), watermelon mosaic virus (WMV), and zucchini yellow mosaic virus (ZYMV) (Cai et al. 2001; Liao et al. 2005; Qin et al. 2005). In August 2017, six S. grosvenorii samples (nos. LHG-1 to LHG-6) that showed mosaic, chlorosis, and mottling of leaves were collected from Yongfu, Guangxi province, China. All symptomatic samples were tested by enzyme-linked immunosorbent assay (ELISA) in double antibody sandwich format for 10 known cucurbit-infecting viruses, including cucumber green mottle mosaic virus (CGMMV), cucumber mosaic virus, kyuri green mottle mosaic virus, PRSV, squash mosaic virus, tobacco mosaic virus (TMV), watermelon silver mottle virus, WMV, zucchini green mottle mosaic virus, and ZYMV. The sample LHG-1 with chlorosis and mottle symptoms reacted positively against the antisera of CGMMV and TMV (Adgen, U.K.) but negatively against antisera of the other viruses. The other samples were negative in ELISA for all viruses tested. Total RNA was extracted from the LHG-1 sample using TRIzol reagent (Takara Dalian, China) following the manufacturer’s instructions. Reverse transcription polymerase chain reaction (RT-PCR) assays using CGMMV-specific primer pair CGM1/CGM2 (Huang et al. 2007) and TMV-specific primers (Li et al. 2000) showed a positive RT-PCR product of the expected size (650 bp) for CGMMV but not for TMV. The amplicon was further cloned into pMD-18-T vector (Takara Dalian) and sequenced (GenBank accession no. MK858182). Sequence analysis revealed that the RT-PCR product showed 99% nucleotide identity to the sequences of CGMMV isolates available in GenBank (accession nos. HM008919, KY753928, KX883833, KP868654, KM873786, and MH271443). The virus in LHG-1 was therefore identified as an isolate of CGMMV and named as CGMMV-LHG. Additionally, to confirm the infectivity of CGMMV-LHG, leaf sap extract in phosphate buffer (0.1 M, pH 7.0) of LHG-1 was mechanically inoculated on leaves of S. grosvenorii and Lagenaria siceraria seedlings. Ten days after inoculation, S. grosvenorii produced symptoms similar to the diseased plants in the field, and systemic mosaic and vein-banding were observed on L. siceraria. The control seedlings inoculated with phosphate buffer remained symptomless. Presence of CGMMV in inoculated plants was confirmed by RT-PCR. To the best of our knowledge, this is the first report of CGMMV infection on S. grosvenorii under natural conditions. The virus can be transmitted by seeds, infects various cucurbit species, and causes yield losses all over the world (Liu et al. 2014; Wu et al. 2011). Use of virus-free seeds and seedlings will be helpful to control CGMMV in S. grosvenorii production areas.

High-Throughput Sequencing Reveals Bell Pepper Endornavirus Infection in Pepper (Capsicum annum) in Slovakia and Enables Its Further Molecular Characterization

Ribosomal RNA-depleted total RNAs from a sweet pepper plant (Capsicum annuum, labelled as N65) grown in western Slovakia and showing severe virus-like symptoms (chlorosis, mottling and deformation of leaf lamina) were subjected to high-throughput sequencing (HTS) on an Illumina MiSeq platform. The de novo assembly of ca. 5.5 million reads, followed by mapping to the reference sequences, revealed the coinfection of pepper by several viruses; i.e., cucumber mosaic virus (CMV), watermelon mosaic virus (WMV), pepper cryptic virus 2 (PCV2) and bell pepper endornavirus (BPEV). A complete polyprotein-coding genomic sequence (14.6 kb) of BPEV isolate N65 was determined. A comparison of BPEV-N65 sequences with BPEV genomes available in GenBank showed 86.1% to 98.6% identity at the nucleotide level. The close phylogenetic relationship with isolates from India and China resulted in their distinct grouping compared to the other BPEV isolates. Further analysis has revealed the presence of BPEV in sweet or chili peppers obtained from various sources and locations in Slovakia (plants grown in gardens, greenhouse or retail shop). Additionally, the partial sequencing of two genomic portions from 15 BPEV isolates revealed that the Slovak isolates segregated into two molecular clusters, indicating a genetically distinct population (mean inter-group nucleotide divergence reaching 12.7% and 14.5%, respectively, based on the genomic region targeted). Due to the mix infections of BPEV-positive peppers by potato virus Y (PVY) and/or CMV, the potential role of individual viruses in the observed symptomatology could not be determined. This is the first evidence and characterization of BPEV from the central European region.

Soybean RNA interference lines silenced for eIF4E show broad potyvirus resistance.

Soybean mosaic virus (SMV), a potyvirus, is the most prevalent and destructive viral pathogen in soybean‐planting regions of China. Moreover, other potyviruses, including bean common mosaic virus (BCMV) and watermelon mosaic virus (WMV), also threaten soybean farming. The eukaryotic translation initiation factor 4E (eIF4E) plays a critical role in controlling resistance/susceptibility to potyviruses in plants. In the present study, much higher SMV‐induced eIF4E1 expression levels were detected in a susceptible soybean cultivar when compared with a resistant cultivar, suggesting the involvement of eIF4E1 in the response to SMV by the susceptible cultivar. Yeast two‐hybrid and bimolecular fluorescence complementation assays showed that soybean eIF4E1 interacted with SMV VPg in the nucleus and with SMV NIa‐Pro/NIb in the cytoplasm, revealing the involvement of VPg, NIa‐Pro, and NIb in SMV infection and multiplication. Furthermore, transgenic soybeans silenced for eIF4E were produced using an RNA interference approach. Through monitoring for viral symptoms and viral titers, robust and broad‐spectrum resistance was confirmed against five SMV strains (SC3/7/15/18 and SMV‐R), BCMV, and WMV in the transgenic plants. Our findings represent fresh insights for investigating the mechanism underlying eIF4E‐mediated resistance in soybean and also suggest an effective alternative for breeding soybean with broad‐spectrum viral resistance.

First report of watermelon mosaic virus isolated from Sicyos angulatus in Korea

First report of watermelon mosaic virus isolated from Sicyos angulatus in Korea

QTL mapping of resistance to Fusarium oxysporum f. sp. niveum race 2 and Papaya ringspot virus in Citrullus amarus.

A Citrullus amarus mapping population segregating for resistance to Fusarium oxysporum f. sp. niveum race 2 and Papaya ringspot virus was used to identify novel QTL, important for the improvement in watermelon disease resistance. Multiple disease screens of the USDA Citrullus spp. germplasm collection have highlighted the value of Citrullus amarus (citron melon or wild watermelon) as a resource for enhancing modern watermelon cultivars (Citrullus lanatus) with resistance to a broad range of fungal, bacterial and viral diseases of watermelon. We have generated a genetic population of C. amarus segregating for resistance to two important watermelon diseases: Fusarium wilt (caused by the fungus Fusarium oxysporum f. sp. niveum; Fon race 2) and Papaya ringspot virus-watermelon strain (PRSV-W). QTL mapping of Fon race 2 resistance identified seven significant QTLs, with the major QTL representing a novel genetic source of resistance and an opportunity for gene pyramiding. A single QTL was associated with resistance to PRSV-W, which adhered to expectations of a prior study indicating a single-gene recessive inheritance in watermelon. The resistance loci identified here provide valuable genetic resources for introgression into cultivated watermelon for the improvement in disease resistance.

First Report of Tomato Leaf Curl New Delhi Virus Infecting Cucurbit Plants in Algeria

HomePlant DiseaseVol. 103, No. 12First Report of Tomato Leaf Curl New Delhi Virus Infecting Cucurbit Plants in Algeria PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Tomato Leaf Curl New Delhi Virus Infecting Cucurbit Plants in AlgeriaA. Kheireddine, A. Sifres, C. Sáez, B. Picó, and C. LópezA. KheireddineInstitute for the Conservation and Breeding of Agricultural Biodiversity, Universitat Politècnica de València, 46022 Valencia, SpainUniversity Mohamed Khider Biskra, 07000 Biskra, AlgeriaSearch for more papers by this author, A. SifresInstitute for the Conservation and Breeding of Agricultural Biodiversity, Universitat Politècnica de València, 46022 Valencia, SpainSearch for more papers by this author, C. SáezInstitute for the Conservation and Breeding of Agricultural Biodiversity, Universitat Politècnica de València, 46022 Valencia, SpainSearch for more papers by this author, B. PicóInstitute for the Conservation and Breeding of Agricultural Biodiversity, Universitat Politècnica de València, 46022 Valencia, SpainSearch for more papers by this author, and C. López†Corresponding author: C. López; E-mail Address: clopez@upvnet.upv.eshttp://orcid.org/0000-0001-7459-1315Institute for the Conservation and Breeding of Agricultural Biodiversity, Universitat Politècnica de València, 46022 Valencia, SpainSearch for more papers by this author AffiliationsAuthors and Affiliations A. Kheireddine1 2 A. Sifres1 C. Sáez1 B. Picó1 C. López1 † 1Institute for the Conservation and Breeding of Agricultural Biodiversity, Universitat Politècnica de València, 46022 Valencia, Spain 2University Mohamed Khider Biskra, 07000 Biskra, Algeria Published Online:16 Oct 2019https://doi.org/10.1094/PDIS-05-19-1118-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat In June 2018, zucchini (Cucurbita pepo), melon (Cucumis melo), and cucumber (Cucumis sativus) plants showing virus-like symptoms such as foliar yellowing and vein clearing were observed in the agricultural region of Biskra, in northeast Algeria. A total of 51 symptomatic leaf samples were collected: 31 of zucchini, 12 of cucumber, and eight of melon. To investigate the etiology of the observed disease, leaf extracts were subjected to total RNA extraction with TRIzol reagent. Virus identification was carried out by nucleic acid spot hybridization using specific riboprobes for tomato leaf curl New Delhi virus (ToLCNDV, genus Begomovirus, family Geminiviridae), cucurbit yellows stunting disorder virus, cucumber vein yellowing virus, cucumber mosaic virus, watermelon mosaic virus, Moroccan watermelon mosaic virus, Algerian watermelon mosaic virus, zucchini yellow mosaic virus, and cucumber green mottle mosaic virus. A hybridization signal was observed for all symptomatic leaf samples with the ToLCNDV riboprobe, whereas no signal was observed for samples from zucchini plants grown in a virus-free facility. Moreover, the presence of any of the other abovementioned viruses was not observed in any of the analyzed samples. To confirm the identity of the virus, DNA was isolated from 24 symptomatic samples (12 of zucchini, six of melon, and six of cucumber) with the CTAB method and was subsequently analyzed by PCR with two ToLCNDV-specific primer pairs (To-A1F and To-A1R from the DNA-A; To-B1F and To-B1R from the DNA-B) (Sáez et al. 2016) to amplify 505- and 677-bp fragments of viral DNAs A and B, respectively. PCR products of the expected size were observed on 1% agarose gel for all of the symptomatic samples. Two randomly selected PCR fragments of each host were bidirectionally sequenced and confirmed as ToLCNDV. The nucleotide sequences of these amplicons were essentially identical irrespective of the host. The complete DNA-A and DNA-B genomic sequences of a ToLCNDV isolate from cucumber (ToLCNDV-Biskra) were obtained as described by Sifres et al. (2018) and deposited in GenBank under accessions numbers MK981891 and MK981892. Alignments of the obtained sequences of DNA-A and DNA-B using the Muscle method in SDT version 1.2 (Muhire et al. 2014) revealed identities of 98.7 and 97.6%, respectively, with the corresponding segments of the isolates from the Mediterranean basin, whereas the identity with isolates from Asia was around 90 and 81% for DNA-A and DNA-B, respectively. Tests conducted by PCR with conserved primers for betasatellites and alphasatellites (Briddon et al. 2002; Bull et al. 2003) were negative, and an additional test by PCR with conserved primers for begomoviruses (Alfaro-Fernández et al. 2016) did not detect any other begomovirus. Moreover, because the Mediterranean basin isolates are mechanically transmitted (López et al. 2015), experiments were conducted using dehydrated tissue of some of the cucumber plants naturally infected with ToLCNDV as a source of inoculum to inoculate seedlings of zucchini accession MU-CU-16, highly susceptible to this virus. Ten days postinoculation, ToLCNDV infection was confirmed by PCR amplification and additionally confirmed by DNA sequencing. In the Mediterranean basin, ToLCNDV has been reported in Spain, Italy, Greece, Tunisia, and Morocco infecting different cucurbit crops, but to our knowledge, this is the first report of the presence of ToLCNDV in Algeria. Further disease monitoring and the establishment of effective control measures will be necessary for disease management to minimize yield losses.The author(s) declare no conflict of interest.

Assessing the Impact on Virus Transmission and Insect Vector Behavior of a Viral Mixed Infection in Melon.

Mixed viral infections in plants are common, and can result in synergistic or antagonistic interactions. Except in complex diseases with severe symptoms, mixed infections frequently remain unnoticed, and their impact on insect vector transmission is largely unknown. In this study, we considered mixed infections of two unrelated viruses commonly found in melon plants, the crinivirus cucurbit yellow stunting disorder virus (CYSDV) and the potyvirus watermelon mosaic virus (WMV), and evaluated their vector transmission by whiteflies and aphids, respectively. Their dynamics of accumulation was analyzed until 60 days postinoculation (dpi) in mixed-infected plants, documenting reduced titers of WMV and much higher titers of CYSDV compared with single infections. At 24 dpi, corresponding to the peak of CYSDV accumulation, similar whitefly transmission rates were obtained when comparing either individual or mixed-infected plants as CYSDV sources, although its secondary dissemination was slightly biased toward plants previously infected with WMV, regardless of the source plant. However, at later time points, mixed-infected plants partially recovered from the initially severe symptoms, and CYSDV transmission became significantly higher. Interestingly, aphid transmission rates both at early and late time points were unaltered when WMV was acquired from mixed-infected plants despite its reduced accumulation. This lack of correlation between WMV accumulation and transmission could result from compensatory effects observed in the analysis of the aphid feeding behavior by electrical penetration graphs. Thus, our results showed that mixed-infected plants could provide advantages for both viruses, directly favoring CYSDV dissemination while maintaining WMV transmission.

Biological control of papaya aphid (Aphis gossypii Glover) using entomopathogenic fungi

Papaya is economically important cultivated fruit crop grown in all tropical countries, having enormous nutritional values. Papaya Ring Spot Virus imposes a significant crop loss in terms of quality and quantity. To encounter the virus vector (Aphis gossypii), indiscriminate use of chemical pesticides creates severe environmental hazards whereas biological control is a perfect alternative to this problem. The objectives of our present study were isolation and characterization of indigenous fungi and their comparative analysis of entomopathogenic fungi against papaya aphid and finding its pathogenicity. Fungal isolates collected from natural sources were characterized and identified by the cultural and morphological study. Potential EPF genera were molecularly identified by PCR (ITS1-5.8S-ITS2) method. Entomopathogenic fungi were screened against A. gossypii for their pathogenecity by incised leaf disc method. LD50 (median lethal dose) and LT50 (median lethal time) were analyzed by regression analysis. Phylogenetic relationship among EPF was evaluated by MEGA software. Out of forty isolated entomopathogenic fungi, three (Beauveria bassiana deb4, Penicillium verrucosum Nlg1, and Fusarium equiseti khr4) were highly effective entomopathogen. The LD50 value of B. bassiana, P. verrucosum and F. equiseti were 1.4 × 104, 9.8 × 104, 1.0 × 106 spores ml−1, and LT50 values were 32.14, 37.5, 32.14 h respectively. Their phylogenetic analysis indicates related closeness on the basis of their conserved internal transcribed spacer region. In conclusion, the indigenous isolated strain of B. bassiana (deb4) has shown highest biocontrol potentiality amongst three indigenous entomopatogenic fungi under lab condition against A. gossypii and can be applied in agrifields.

First Report of Cucurbit Aphid-Borne Yellows Virus in Cucurbita pepo and Cucurbita maxima in Slovenia

First Report of Cucurbit Aphid-Borne Yellows Virus in <i>Cucurbita pepo</i> and <i>Cucurbita maxima</i> in Slovenia

Detection of disease in Cucurbita maxima Duch. ex Lam. caused by a mixed infection of Zucchini yellow mosaic virus, Watermelon mosaic virus, and Cucumber mosaic virus in Southeast China using a novel small RNA sequencing method.

The genus Cucurbita comprises many popular vegetable and ornamental plants, including pumpkins, squashes, and gourds, that are highly valued in China as well as in many other countries. During a survey conducted in Zhejiang province, Southeast China in 2016, severe symptoms of viral infection were observed on Cucurbita maxima Duch. ex Lam. Diseased plants showed symptoms such as stunting, mosaicking, Shoe string, blistering, yellowing, leaf deformation, and fruit distortion. Approximately, 50% of Cucurbita crops produced in Jinhua were diseased, causing an estimated yield loss of 35%. In this study, we developed a method using all known virus genomes from the NCBI database as a reference to map small RNAs to develop a diagnostic tool that could be used to diagnose virus diseases of C. maxima. 25 leaf samples from different symptomatic plants and 25 leaf samples from non-symptomatic plants were collected from the experimental field of Jihua National Agricultural Technology Garden for pathogen identification. Small RNAs from each set of three symptomatic and non-symptomatic samples were extracted and sequenced by Illumina sequencing. Twenty-four different viruses were detected in total. However, the majority of the small RNAs were from Zucchini yellow mosaic virus (ZYMV), Watermelon mosaic virus (WMV), and Cucumber mosaic virus (CMV). Mixed infections of these three viruses were diagnosed in leaf samples from diseased plants and confirmed by reverse transcription PCR (RT-PCR) using primers specific to these three viruses. Crude sap extract from symptomatic leaf samples was mechanically inoculated back into healthy C. maxima plants growing under greenhouse conditions. Inoculated plants developed the same disease symptoms as those observed in the diseased plants and a mixed infection of ZYMV, WMV, and CMV was detected again by RT-PCR, thus fulfilling Koch’s postulates. The diagnostic method developed in this study involves fewer bioinformatics processes than other diagnostic methods, does not require complex settings for bioinformatics parameters, provides a high level of sensitivity to rapidly diagnose plant samples with symptoms of virus diseases and can be performed cheaply. This method therefore has the potential to be widely applied as a diagnostic tool for viruses that have genome information in the NCBI database.

DsRNA-mediated protection against two isolates of Papaya ringspot virus through topical application of dsRNA in papaya

Papaya ringspot virus (PRSV) infections in papaya result in heavy yield losses, severely affecting the papaya industry worldwide, and hence warranting for effective control measures. In the past, transgenic papaya cultivars were developed that overexpressed parts of the PRSV genome and exhibited high levels of virus resistance. In the present study, a non-transgenic approach was employed, in which in vitro produced dsRNA molecules derived from a PRSV isolate from South India (PRSV-Tirupati) was tested for dsRNA-mediated protection against two isolates of PRSV through topical application of the dsRNA on papaya. The results showed that the dsRNA molecules from both the coat protein (CP) and helper component-proteinase (HC-Pro) genes of the PRSV-Tirupati isolate conferred 100 % resistance against PRSV-Tirupati infection. Further, the same dsRNA molecules were highly effective against the PRSV-Delhi isolate on the papaya cv. Pusa Nanha, conferring a resistance of 94 % and 81 %, respectively. Systemic papaya leaves of the dsRNA-treated plants were virus-free at 14 days post-inoculation, confirming the robustness of this non-transgenic virus control strategy. In contrast, the control TMV dsRNA did not protect against the PRSV infection. This study on the topical application of dsRNA opened up a new avenue for the control of papaya ringspot disease worldwide.

Papaya Ringspot Virus Isolates From Papaya in Bangladesh: Detection, Characterization, and Distribution.

Papaya ringspot virus (PRSV) is the major constraint to papaya (Carica papaya) production in Bangladesh. Disease symptoms occurred in 90 to 100% of the plants surveyed. Full-length genomes of PRSV strains from severely infected papaya plants were determined using the Illumina NextSeq 500 platform, followed by Sanger DNA sequencing of viral genomes obtained by reverse-transcription PCR(RT-PCR). The genome sequences of two distinct PRSV strains, PRSV BD-1 (10,300 bp) and PRSV BD-2 (10,325 bp) were 74 and 83% identical to each other, respectively, at the nucleotide and amino acid levels. PRSV BD-1 and PRSV BD-2 were 74 to 75% and 79 to 88% identical, respectively, to other full-length PRSV sequences at the nucleotide level. Based on phylogenetic analysis, PRSV BD-2 was most closely related to PRSV-Meghalaya (MF356497) from papaya in India. PRSV BD-1 formed a branch distinct from the other PRSV sequences based on nucleotide and amino acid sequence comparisons. Comparisons of the genome sequences of these two strains with other sequenced PRSV genomes indicated two putative recombination events in PRSV BD-2. One recombinant event contained a 2,766-nucleotide fragment highly identical to PRSV-Meghalaya (MF356497). The other recombinant event contained a 5,105-nucleotide fragment highly identical to PRSV-China (KY933061). The occurrence rates of PRSV BD-1 and PRSV BD-2 in the sampled areas of Bangladesh were approximately 19 and 69%, respectively. Plants infected with both strains (11%) exhibited more severe symptoms than plants infected with either strain alone. The full-length genome sequences of these new PRSV strains and their distribution provide important information regarding the dynamics of papaya ringspot virus infections in papaya in Bangladesh.

Selection of watermelon accessions for resistance to some important potyvirus species based on serological evaluation

We used 19 genotypes (plus controls) of watermelon from the collection of Cucurbitaceas germplasm of the Federal Rural University of the Semi-Arid to select watermelon plants resistant to Papaya ringspot virus “type Watermelon” (PRSV-W), Watermelon mosaic virus (WMV), and Zucchini yellow mosaic virus (ZYMV). Twenty individual plants were tested for each genotype/accession. Three controls were also used (3 genotypes). Evaluations were performed under greenhouse in a completely randomized design with five replications. The first inoculation was performed on the seedlings before the appearance of the first definitive leaf. From each accession (genotype) 20 different individual plants were inoculated with the three viruses. The inoculum was prepared by infected leaf tissue. The viral suspension and gauze soaked in extract were wiped on the surface of the leaves. Ten days later, the symptom assessment was performed. Subsequently, the plants were individually tested against the specific viruses using indirect ELISA. ELISA negative plants were submitted to a second inoculation under greenhouse, as described for the first inoculation. Ten days after new inoculation, new symptomatological evaluations and serological tests were performed to confirm the resistance of the plants. Plants that were negative by ELISA were tested by RT-PCR for confirmation of resistance. Resistance to the three viruses was verified individually in several tested genotypes. We found resistance to the three viruses tested, but in different plant individuals, where 16 individual plants were WMV-resistant, 26 PRSV-W resistant and 30 ZYMV-resistant. These plants can be used to develop homozygous lines for resistance to the virus studied.

Revisiting cross-protection in the form of antagonism: the case of Papaya mosaic virus protecting papaya plants against Papaya ringspot virus

Cross-protection has been defined as the initial inoculation of a mild strain of a virus protecting plants against a severe strain. As the elucidation of the mechanisms that underlie this phenomenon evolves, we propose that this concept extends to the use of different species of viruses, where a mild species [Papaya mosaic virus (PapMV), a potexvirus] protects against other severe species [Papaya ringspot virus (PRSV), a potyvirus] in papaya plants.

Papaya greenhouse cultivation in south-east Spain

Spain is the leading producer of tropical fruit crops in Europe. Within Spain, papaya cultivation is concentrated in the Canary Islands, where 350 ha are planted and 16,000 t produced annually. Recently, papaya has also been introduced into the south-east of Spain. More than 100 ha of papaya orchards under protected cultivation have now planted in south-east Spain. This region has a subtropical, semiarid, Mediterranean climate with a hot and dry summer and a mild winter, with high temperatures in summer (above 40°C) and low ones in winter (sometimes below 10°C) being the main climate challenges. Papaya cultivation in south-east Spain takes place very often in low-technology parral greenhouses, 3.5-4 m tall, covered with plastic and only provided with natural ventilation. In order to improve the climate inside greenhouses, different systems of nebulization and heating are being evaluated. ‘Intenzza’, a ‘Formosa’ hybrid from Mexico, is so far the most planted cultivar. Other cultivars under cultivation are ‘Siluet’, ‘Sweet Sense’, ‘Tainung’, ‘BH-65’ and ‘Caballero’. Papaya multiplication is by seed, but the use of molecular markers to determine papaya sex allows rapid selection of hermaphrodite plants in the nursery. This technique makes crop management easier. Plant density ranges from 1600 to 2700 plants ha(‑1), transplanted more frequently in spring (March-April), although transplanting at other times of year is also possible. Harvest begins 7 months after transplanting. The yield reaches 200 t ha(‑1) and shows two peaks, one after winter and the other after summer. The main pest so far observed is the red mite, while the most important diseases are powdery mildew and botrytis. There is no record of Papaya ring spot virus (PRSV) incidence in our fields. Given the higher cost of production of papaya in Spain, we believe that the key for the successful introduction of Spanish papaya in European markets is to allow fruit ripening on the tree, and to produce sweet fruits of excellent quality.