Sword Bean (Canavalia gladiata): a new host of Bean common mosaic virus.

BACKGROUND: Sword bean (Canavalia gladiata) is an underutilized legume that has the potential to become an important food source owing to its wide range of nutritional and medicinal properties. In May 2023, symptoms induced by a possible virus infection such as mosaic, mottling and vein banding were observed on the leaves of about 20% of the Sword bean plants growing at the experimental research farm of the Indian Agricultural Research Institute in Pune, Maharashtra, India. METHODS AND RESULTS: Symptomatic and asymptomatic samples were screened by ELISA for the presence of Potyvirus, Cucumber mosaic virus and Tobacco mosaic virus. All symptomatic samples tested positive for Potyvirus in ELISA as well as in RT-PCR assay using the universal potyvirus primer pair (CPUP /P9502) which amplify c. 700 bp of the partial coat protein region and 3'UTR. Asymptomatic samples tested negative for all tested viruses in both serological and molecular assays. BLASTn sequence analysis of the amplicons revealed that the sequence shares more than 98% identity with an Indian isolate of Bean common mosaic virus (BCMV). Sequence analysis enabled the identification of the Potyvirus as BCMV. Furthermore, the present Sword bean isolate clustered with other BCMV isolates in the phylogenetic analysis. CONCLUSION: In the present study, BCMV was found to be naturally infecting Sword bean for the first time in the world. This is of epidemiological importance, as BCMV is known to cause significant yield losses in legumes and could severely hamper Sword bean production.

First Report of Cucurbit aphid-borne yellows virus infecting five cucurbits in India.

Cucurbits are among the most popular vegetables cultivated globally. They have high economic importance, especially in India, where they are cooked and eaten as vegetables (Dhillon et al. 2016). In February 2023, yellowing symptoms were observed on cucurbitaceous species, viz. Trichosanthes cucumerina (Snake gourd - SG), Luffa acutangula (Ridge gourd - RG), Lagenaria siceraria (Bottle gourd - BG), Luffa aegyptiaca (Sponge gourd - SPG) and yellow chlorotic spots were recorded on Benincasa hispida (Ash gourd - AG) growing in the experimental farm at the Indian Agricultural Research Institute, Regional Station, Pune (Supplementary Figure 1). The average disease incidence ranged from 5% to 30%. A total of 175 leaf samples, including thirty symptomatic and five asymptomatic plants of each cucurbit, were collected and tested by DAS-ELISA using antisera against cucurbit aphid-borne yellows virus (CABYV) (DSMZ, Germany), cucurbit yellow stunting disorder virus (CYSDV) (Arsh Biotech, India), cucumber mosaic virus (CMV), zucchini yellow mosaic virus (ZYMV), and papaya ringspot virus (PRSV) (Agdia, USA). All 150 symptomatic cucurbit samples tested positive for CABYV, while five samples from SG, 14 from RG, two from AG, and 11 from SPG hosts were also positive for PRSV. Asymptomatic samples were negative for all viruses tested. In order to further confirm the presence of the virus, total RNA was extracted from ten samples of each cucurbit host that were positive only for CABYV and the asymptomatic samples using the RNeasy Plant Mini Kit (Qiagen, Germany) as per the manufacturer's protocol. Two-step RT-PCR was carried out using the extracted RNA and CABYV-specific primers, amplifying c. 484 bp of the coat protein gene region (Boubourakas et al. 2006). Amplicons of expected size were obtained in all symptomatic samples, whereas the asymptomatic samples tested negative. Three amplicons obtained from positive samples from each of the cucurbit species were directly sequenced and found to be identical to each other. A representative virus sequence obtained from each cucurbit was deposited in GenBank (Snake gourd - OQ921128, Ridge gourd - OQ921127, Bottle gourd - OQ921126, Ash gourd - OQ921125, Sponge gourd - OQ921129). In BLASTn analysis, the isolates shared from 94.23 to 100% nucleotide identities with the Indian CABYV isolates of various cucurbits and clustered closely with other Pune isolates in the phylogenetic analysis (Supplementary Figure 2). CABYV (genus Polerovirus) is a single-stranded positive-sense RNA virus, and is known to infect and cause severe economic losses in cucurbits worldwide. Previously, occurrences of CABYV have been reported in cucurbits such as watermelon, bitter gourd, cucumber, squash, teasel gourd, and muskmelon in India (Nagendran et al. 2022; Tripathi et al. 2023). It has also been reported to infect a weed species - Abelmoschus moschatus from the same geographical region (Verma et al. 2023). To our knowledge, this is the first report of the natural occurrence of CABYV in snake gourd and ridge gourd worldwide and bottle gourd, ash gourd and sponge gourd in India. The present findings have significant epidemiological importance, as they demonstrate that CABYV is spreading to other cucurbits and occurring widely in India.

Differential expression of microRNAs in response to Papaya ringspot virus infection in differentially responding genotypes of papaya (Carica papaya L.) and its wild relative.

Papaya ringspot virus (PRSV) is one of the most devastating viruses of papaya that has significantly hampered papaya production across the globe. Although PRSV resistance is known in some of its wild relatives, such as Vasconcellea cauliflora and in some of the improved papaya genotypes, the molecular basis of this resistance mechanism has not been studied and understood. Plant microRNAs are an important class of small RNAs that regulate the gene expression in several plant species against the invading plant pathogens. These miRNAs are known to manifest the expression of genes involved in resistance against plant pathogens, through modulation of the plant's biochemistry and physiology. In this study we made an attempt to study the overall expression pattern of small RNAs and more specifically the miRNAs in different papaya genotypes from India, that exhibit varying levels of tolerance or resistance to PRSV. Our study found that the expression of some of the miRNAs was differentially regulated in these papaya genotypes and they had entirely different miRNA expression profile in healthy and PRSV infected symptomatic plants. This data may help in improvement of papaya cultivars for resistance against PRSV through new breeding initiatives or biotechnological approaches such as genome editing.

Aleurothrixus trachoides (Back) can transmit begomovirus from Duranta to potato, tomato and bell pepper.

Solanum whitefly, Aleurothrixus trachoides (Back). (Hemiptera: Aleyrodidae) was considered as a non-virus vector by European and Mediterranean Plant Protection Organization (EPPO) reports. However, in the present study it was found to transmit Duranta leaf curl virus (DLCV) to tomato, bell pepper and potato. A. trachoides infested field samples of Duranta sp (100%) and tomato (20%) tested positive for begomovirus by PCR using begomovirus degenerate primers and primers specific to Tomato leaf curl New Delhi virus showing amplicon of 520 bp and 2.7 Kb respectively. The DNA samples of A. trachoides collected from virus positive duranta and tomato plants also tested positive for the virus. Virulent whiteflies from duranta could successfully transmit DLCV to bell pepper (26%) and tomato (13 %) plants as confirmed by Rolling Circle Amplification. The rate of virus transmission by A. trachoides from DLCV inoculated tomato to bell pepper and tomato to potato was 100% and tomato to tomato was 80%. The results suggest whitefly A. trachoides as the vector for DLCVand to the best of our knowledge, this is the first report for A. trachoides as vector of begomovirus. These findings suggest need for reconsideration of A. trachoides as a virus-vector. This will have great impact on solanaceous vegetable cultivation in India and other parts of the world.

Development of genetically engineered resistant papaya for papaya ringspot virus in a timely manner: a comprehensive and successful approach.

Papaya orchards throughout most of the world are severely damaged by the destructive disease caused by the papaya ringspot virus (PRSV). PRSV-resistant papaya expressing the coat protein gene (CP) of PRSV have been used in Hawaii to control PRSV since 1998. This chapter presents the experimental steps involved in the development of transgenic papaya, including transgene construction, transformation, and analysis for virus resistance of the transformed papaya. We also describe the important factors that enabled deregulation, commercialization, and adoption of transgenic papaya to occur in Hawaii in a timely manner. Transfer of this technology to other countries with the similar goal and the development of transgenic papaya in other regions of the world also are described.

Allergenicity assessment of the papaya ringspot virus coat protein expressed in transgenic rainbow papaya.

The virus-resistant, transgenic commercial papaya Rainbow and SunUp (Carica papaya L.) have been consumed locally in Hawaii and elsewhere in the mainland United States and Canada since their release to planters in Hawaii in 1998. These papaya are derived from transgenic papaya line 55-1 and carry the coat protein (CP) gene of papaya ringspot virus (PRSV). The PRSV CP was evaluated for potential allergenicity, an important component in assessing the safety of food derived from transgenic plants. The transgene PRSV CP sequence of Rainbow papaya did not exhibit greater than 35% amino acid sequence homology to known allergens, nor did it have a stretch of eight amino acids found in known allergens which are known common bioinformatic methods used for assessing similarity to allergen proteins. PRSV CP was also tested for stability in simulated gastric fluid and simulated intestinal fluid and under various heat treatments. The results showed that PRSV CP was degraded under conditions for which allergenic proteins relative to nonallergens are purported to be stable. The potential human intake of transgene-derived PRSV CP was assessed by measuring CP levels in Rainbow and SunUp along with estimating the fruit consumption rates and was compared to potential intake estimates of PRSV CP from naturally infected nontransgenic papaya. Following accepted allergenicity assessment criteria, our results show that the transgene-derived PRSV CP does not pose a risk of food allergy.

Papaya ringspot virus-P: characteristics, pathogenicity, sequence variability and control.

TAXONOMY: Papaya ringspot virus (PRSV) is an aphid-transmitted plant virus belonging to the genus Potyvirus, family Potyviridae, with a positive sense RNA genome. PRSV isolates belong to either one of two major strains, P or W. The P strains infect both papaya and cucurbits whereas the W strains infect only cucurbits. GEOGRAPHICAL DISTRIBUTION: PRSV-P is found in all major papaya-growing areas. PHYSICAL PROPERTIES: Virions are filamentous, non-enveloped and flexuous measuring 760-800 x 12 nm. Virus particles contain 94.5% protein and 5.5% nucleic acid. The protein component consists of the virus coat protein (CP), which has a molecular weight of about 36 kDa as estimated by Western blot analysis. Density of the sedimenting component in purified PRSV preparations is 1.32 g/cm(3) in CsCl. GENOME: The PRSV genome consists of a unipartite linear single-stranded positive sense RNA of 10 326 nucleotides with a 5' terminus, genome-linked protein, VPg. TRANSMISSION: The virus is naturally transmitted via aphids in a non-persistent manner. Both the CP and helper component (HC-Pro) are required for vector transmission. This virus can also be transmitted mechanically, and is typically not seed-transmitted. HOSTS: PRSV has a limited number of hosts belonging to the families Caricaceae, Chenopodiaceae and Cucurbitaceae. Propagation hosts are: Carica papaya, Cucurbita pepo and Cucumis metuliferus cv. accession 2459. Local lesion assay hosts are: Chenopodium quinoa and Chenopodium amaranticolor. CONTROL: Two transgenic papaya varieties, Rainbow and SunUp, with engineered resistance to PRSV have been commercially grown in Hawaii since 1998. Besides transgenic resistance, tolerant varieties, cross-protection and other cultural practices such as isolation and rogueing of infected plants are used to manage the disease. VIRUS CODE: 00.057.0.01.045. VIRUS ACCESSION NUMBER: 57010045. USEFUL LINK: http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/57010045.htm.