After two years since the declaration of COVID-19 as a pandemic by the World Health Organization (WHO), more than six million deaths have occurred due to SARS-CoV-2, leading to an unprecedented disruption of the global economy. Fortunately, within a year, a wide range of vaccines, including pathogen-based inactivated and live-attenuated vaccines, replicating and non-replicating vector-based vaccines, nucleic acid (DNA and mRNA)-based vaccines, and protein-based subunit and virus-like particle (VLP)-based vaccines, have been developed to mitigate the severe impacts of the COVID-19 pandemic. These vaccines have proven highly effective in reducing the severity of illness and preventing deaths. However, the availability and supply of COVID-19 vaccines have become an issue due to the prioritization of vaccine distribution in most countries. Additionally, as the virus continues to mutate and spread, questions have arisen regarding the effectiveness of vaccines against new strains of SARS-CoV-2 that can evade host immunity. The urgent need for booster doses to enhance immunity has been recognized. The scarcity of “safe and effective” vaccines has exacerbated global inequalities in terms of vaccine coverage. The development of COVID-19 vaccines has fallen short of the expectations set forth in 2020 and 2021. Furthermore, the equitable distribution of vaccines at the global and national levels remains a challenge, particularly in developing countries. In such circumstances, the exigency of plant virus-based vaccines has become apparent as a means to overcome supply shortages through fast manufacturing processes and to enable quick and convenient distribution to millions of people without the reliance on a cold chain system. Moreover, plant virus-based vaccines have demonstrated both safety and efficacy in eliciting robust cellular immunogenicity against COVID-19 pathogens. This review aims to shed light on the advantages and disadvantages of different types of vaccines developed against SARS-CoV-2 and provide an update on the current status of plant-based vaccines in the fight against the COVID-19 pandemic.

In tropical countries, combating leaf curl disease in hot peppers has become important in improvement programs. Leaf curl disease is caused by whitefly (Bemisia tabaci) transmitted begomoviruses, which mainly include chilli leaf curl virus (ChiLCV). However, multiple begomoviruses have also been found to be associated with this disease. The Capsicum annuum line, DLS-Sel-10, was found to be a tolerant source against this disease during field screening. In this study, we characterized the resistance of DLS-sel-10 against chilli leaf curl virus (ChiLCV) in comparison to the susceptible cultivar Phule Mukta (PM), focusing on the level, stage, and nature of resistance. Comprehensive investigations involved screening of DLS-Sel-10 against the whitefly vector ChiLCV. The putative tolerant line displayed reduced virus infection at the seedling stage, with increasing resistance during vegetative, flowering, and fruiting stages. Both DLS-Sel-10 and PM could be infected with ChiLCV, although DLS-Sel-10 remained symptomless. Insect feeding assays revealed DLS-Sel-10 as a less preferred host for whiteflies compared to PM. In conclusion, DLS-Sel-10 demonstrated tolerance not only to ChiLCV but also served as an unfavorable host for the whitefly vector. The study highlighted an age-dependent increase in tolerance within DLS-Sel-10, showcasing its potential for effective leaf curl disease management in chilli.

Watermelon production is significantly affected by watermelon bud necrosis virus (WBNV), an economically important orthotospovirus in the Indian subcontinent. RNA interference (RNAi)-based approaches offer promising strategies for developing broad-spectrum antiviral resistance in susceptible plants. In this study, we evaluated the efficacy of foliar application of double-stranded RNA (dsRNA) and hairpin RNA (hpRNA) derived from the full-length NSs gene of WBNV against WBNV infection in two host plants, Nicotiana benthamiana and cowpea (Vigna unguiculata). Fluorescein-labeled dsRNA of NSs gene (dsNSs) was tracked in N. benthamiana plants, where dsNSs translocated from the treated leaf to adjacent leaves, stem, and roots. Naked dsNSs was no longer detectable in treated leaves at 5 days post-inoculation (dpi), whereas mesoporous silica nanoparticle-conjugated dsNSs (dsNSs-MSNP) remained detectable in the treated leaves beyond 5 dpi, indicating enhanced stability. Following WBNV inoculation, N. benthamiana plants treated with hairpin of NSs gene (hpNSs), dsNSs, and dsNSs-MSNP exhibited 112, 303, and 370 fold reduction in viral RNA accumulation, respectively. Although these treatments delayed symptom development, all inoculated plants eventually showed the viral symptoms in N. benthamiana. Similarly, treatment of Vigna unguiculata cv. Pusa Komal (cowpea) plants with hpNSs, dsNSs, and dsNSs-MSNP resulted in reduced viral load, where dsNSs-MSNP provided the maximum reduction up to 208 fold. The dsNSs provided 100% reduction in development of systemic symptoms of bud necrosis disease in the treated cowpea plants. Collectively, these findings demonstrate that foliar application of nanoparticle-conjugated dsRNA targeting the full-length NSs gene can effectively suppress WBNV infection and provide enhanced protection against disease development in cowpea.