Evidence for the natural infection of cucurbit chlorotic yellows virus (CCYV) in lettuce plants from India.

In the years 2021 and 2022, lettuce plants showing blistering, chlorosis, mosaic, rosetting/ excess proliferation, and stunting symptoms were subjected to leaf-dip transmission electron microscopy, RT-PCR followed by sequence analysis and bio-assay to unfold the identity of associated virus(es). The association of long filamentous virions (~ 850 nm in length) as seen through leaf-dip transmission electron microscopy suggested the possible infection by a potyvirus or crinivirus, either singly or in combination. RT-PCR assays using generic primers targeting the RdRp region of criniviruses and the NIb region of potyviruses revealed the association of both a crinivirus as well as a potyvirus. The gel-purified RT-PCR products derived from the RdRp region of criniviruses upon cloning, sequencing, and NCBI BLAST analysis indicated the associated crinivirus as cucurbit chlorotic yellows virus (CCYV). Further, RT-PCR assays using specific primers targeting CP and CP minor genes of CCYV followed by cloning and sequencing confirmed its association with the diseased lettuce plants. Besides, the bioassay based on whitefly-mediated virus transmission followed by RT-PCR confirmed the infectivity of CCYV from diseased to healthy lettuce plants. The results of this study confirmed the natural infection of CCYV in lettuce host for the first time in the world indicating its distribution across the crop families.

Molecular evidence for the occurrence of Pumpkin yellows virus (PuYV), a new polerovirus species associated with pumpkin plants.

In India, cucurbit aphid-borne yellows virus, a cucurbit-infecting polerovirus, is emerging in the recent past with respect to its occurrence on different crops and geographical locations. This emphasized the need for an investigation to search for the possible occurrence of the other related species Polerovirus. In this view, different cucurbit hosts exhibiting severe chlorosis, bleaching, and yellowing symptoms were collected from the Vegetable Experimental Fields of IARI, New Delhi. The samples exhibiting yellowing and bleaching symptoms were associated with small isometric virions measuring ~ 25 nm under transmission electron microscope. The RT-PCR assays using generic (covering the partial RdRp, intergenic region and partial CP region) and complete coat protein (CP) gene-specific primers confirmed the association of a polerovirus. Further, complete CP gene sequence analyses revealed the association of a distinct species of Polerovirus with the pumpkin samples. These isolates showed the CP gene sequence identities below the species demarcation limit (90%) with the corresponding gene sequences of already reported polerovirus isolates. The results of this study provide the molecular evidence for the occurrence of a new species of Polerovirus, named tentatively as Pumpkin yellows virus (PuYV) in India.

Direct Foliar Application of dsRNA Derived From the Full-Length Gene of NSs of Groundnut Bud Necrosis Virus Limits Virus Accumulation and Symptom Expression.

Groundnut bud necrosis virus (GBNV) is the most significant member of the genus Orthotospovirus occurring in the Indian subcontinent. There is hardly any effective measure to prevent GBNV in crop plants. In order to develop GBNV infection prevention procedure, we examined the effect of the direct foliar application of double-stranded RNA (dsRNA) derived from the full-length NSs gene (1,320 nucleotides) of GBNV. The bacterially expressed dsRNA to the non-structural (dsNSs) gene of GBNV was purified and delivered to plants as an aqueous suspension containing 0.01% Celite for evaluating its efficacy in preventing GBNV infection in systemic host, Nicotiana benthamiana as well as in local lesion and systemic host, cowpea cv. Pusa Komal (Vigna unguiculata). The dsNSs application and challenge-inoculation were conducted in three different combinations, where plants were challenge-inoculated with GBNV a day after, immediately, and a day before the application of dsNSs. N. benthamiana plants, which were not treated with dsRNA showed severe systemic wilting and death by 9-16 days post-inoculation (dpi). The non-treated cowpea plants exhibited many chlorotic and necrotic lesions on the cotyledonary leaves followed by systemic necrosis and death of the plants by 14-16 dpi. The dsNSs treated plants in all the combinations showed significant reduction of disease severity index in both N. benthamiana and cowpea. The treatment combination where the GBNV inoculation was conducted immediately after the dsNSs treatment was found to be the most effective treatment in preventing symptom expression. The viral RNA analysis by real time PCR also showed 20 and 12.5 fold reduction of GBNV in cowpea and N. benthamiana, respectively. Our results suggest that the foliar application of dsRNA derived from the full-length NSs gene of GBNV through Celite is successful in delivering long dsRNA leading to effective prevention of GBNV infection.

Graphene oxide based electrochemical immunosensor for rapid detection of groundnut bud necrosis orthotospovirus in agricultural crops.

Groundnut bud necrosis orthotospovirus (GBNV) is one of the causative plant viruses responsible for the outbreak of many viral epidemics in food crops across India and other south-Asian countries. Its management is a major challenge due to fast vector transmission, and the non-availability of appropriate agrochemical treatment. The timely detection of GBNV becomes indispensable for the effective management of viral infection and the periodic monitoring of plant health. We report the fabrication of graphene oxide (GO) based electrochemical immunosensor for the rapid and sensitive detection of GBNV. The immunoelectrode is prepared by depositing GO onto indium-tin oxide (ITO) coated glass substrates and functionalized by anti-GBNV antibodies using N-ethyl-N'-(3- dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide (EDC-NHS) conjugation chemistry. The response measurements of the immunoelectrodes revealed a sensitivity of 221 ± 1 µA µg-1 mL-1(n = 3) and limit of detection (LOD) of 5.7 ± 0.7 ng mL-1(n = 3) for the standard concentrations of GBNV antigen. Further, the GBNV detection was carried out in infected leaf extracts of three different host plants i.e., Tomato, Cowpea, and N. benthamiana, and the results have been compared with the conventionally used direct antigen coated enzyme-linked immunosorbent assay (DAC-ELISA) technique. The comparable results obtained for the detection of GBNV in infected plants using electrochemical immunosensing and DAC-ELISA techniques advocated the immense potential of GO based immunosensor as a point-of-care sensing device that is poised to overcome the limitations of the traditional methods of virus detection in field conditions and may transform the diagnostics in agriculture.

Association of cucurbit aphid-borne yellows virus with cucumber plants in India.

Symptoms like bright yellowing, puckering of the leaf, vein banding, and vein thickening were observed on different cucurbit hosts at the experimental farm of Indian Agricultural Research Institute, New Delhi during Kharif 2019. Leaf-dip electron microscopy of the symptomatic leaves revealed the association of isometric virus particles measuring ~ 25 nm with bitter gourd and cucumber samples. The RT-PCR assay using polerovirus generic primers covering the partial RdRp, intergenic region, and partial CP region was resulted the amplicons of ~ 1.1 kb. Subsequent cloning, sequencing, and sequence analysis revealed the association of cucurbit aphid-borne yellows virus (CABYV) with bitter gourd (Momordica charantia) and cucumber (Cucumis sativus) plants. These results constitute the first report of CABYV infection on cucumber plants from India. SUPPLEMENTARY INFORMATION: The online version of this article (10.1007/s13337-020-00645-4) contains supplementary material, which is available to authorized users.

Exposure to watermelon bud necrosis virus and groundnut bud necrosis virus alters the life history traits of their vector, Thrips palmi (Thysanoptera: Thripidae).

Thrips palmi transmits the tospoviruses watermelon bud necrosis (WBNV) and groundnut bud necrosis virus (GBNV) in persistent propagative way. Little is known about the T. palmi-WBNV and -GBNV relationship. In this study, we report the effects of WBNV and GBNV infection on the life history traits of T. palmi. Both WBNV and GBNV had some negative effects on the adult life span, fecundity and survival of T. palmi as compared to non-exposed T. palmi. Tospovirus exposure favoured a female-biased ratio in the experimental population.

Genetic Diversity Based on Coat Protein of Papaya ringspot virus (Pathotype P) Isolates from Bangladesh.

The coat protein (CP) sequences of twelve Papaya ringspot virus (PRSV) (pathotype-P) isolates from six major papaya growing areas were determined and compared with those of published PRSV. The CP coding region varied in size from 846-852 nucleotides, encoding a protein of 282-284 amino acids. Comparative CP sequence analysis revealed that the PRSV-P isolates originating from Bangladesh were divergent up to 14 % at amino acids level. Further, the isolates from Bangladesh shared 86-95 % amino acid sequence identity with those reported from rest 21 of the Asia and 83-93 % amino acid sequence identity with isolates from the other parts of the world. A number of KE repeats were observed in the N terminus of the CP coding region of all Bangladesh isolates. Phylogenetic branching pattern revealed that the PRSV-P isolates originating from Bangladesh formed a distinct clade from those from the rest of the world. This forms the first report on the genetic diversity of PRSV-P isolates from Bangladesh.