Severe acute respiratory syndrome coronavirus 2, SARS-CoV-2, arose at the end of 2019 as a zoonotic virus, which is the causative agent of the novel coronavirus outbreak COVID-19. Without any clear indications of abatement, the disease has become a major healthcare threat across the globe, owing to prolonged incubation period, high prevalence, and absence of existing drugs or vaccines. Development of COVID-19 vaccine is being considered as the most efficient strategy to curtail the ongoing pandemic. Following publication of genetic sequence of SARS-CoV-2, globally extensive research and development work has been in progress to develop a vaccine against the disease. The use of genetic engineering, recombinant technologies, and other computational tools has led to the expansion of several promising vaccine candidates. The range of technology platforms being evaluated, including virus-like particles, peptides, nucleic acid (DNA and RNA), recombinant proteins, inactivated virus, live attenuated viruses, and viral vectors (replicating and non-replicating) approaches, are striking features of the vaccine development strategies. Viral vectors, the next-generation vaccine platforms, provide a convenient method for delivering vaccine antigens into the host cell to induce antigenic proteins which can be tailored to arouse an assortment of immune responses, as evident from the success of smallpox vaccine and Ervebo vaccine against Ebola virus. As per the World Health Organization, till January 22, 2021, 14 viral vector vaccine candidates are under clinical development including 10 nonreplicating and four replicating types. Moreover, another 39 candidates based on viral vector platform are under preclinical evaluation. This review will outline the current developmental landscape and discuss issues that remain critical to the success or failure of viral vector vaccine candidates against COVID-19.

Cut-shoot bioassay test was used to study the significance of three flavonoids as aphicides against the woolly apple aphid (WAA), Eriosoma lanigerum (Hausmann). The used flavonoids were two flavanols that are quercetin dehydrate and rutin hydrate, but rutin hydrate is a glycoside of quercetin dehydrate. In addition to one flavanone that was naringine. These flavonoids were used at three concentrations; 100 ppm, 1000 ppm and 10,000 ppm. Results showed that the three tested flavonoids were active as aphicides against the target species and that mortality to nymphs was higher than that obtained against apterous adults. Increasing the concentration of the flavonoids resulted in a remarkable increase in nymphs mortality. However, rutin hydrate is more toxic to WAA than quercetin dehydrate and naringin.The three flavonoids had slight effect on the sole parasitoid of WAA, Aphelinus mali compared with effect caused by imodacloprid insecticide. Quercetin dehydrate, rutin hydrate and naringine can be used as botanical insecticides and incorporated into integrated management programs of the aphid.

Successful clonal propagation of Stevia rebaudiana was achieved using microshoots as a primary step for in vitro conservation. Maximum proliferation was obtained on Murashige and Skoog (MS) medium supplemented with 1.5 mg L -1 benzyl amino purine and 0.2 mg L -1 indole-3-butyric-acid (IBA). Auxin increased rooting percentage of shoots at concentration of 0.4 mg L -1 IBA, indole-3-acetic-acid or naphthalene acetic acid and no rooting occurred without plant growth regulator. A survival of 90% was achieved when rooted explants were acclimatized in vivo in 1 soil: 1 perlite: 1 peat. In vitro S. rebaudiana shoots were successfully stored for up to 32 weeks on MS medium supplemented with an appropriate concentration of sucrose, sorbitol or mannitol, at 24 ± 2°C. After 32 weeks, 93.6% of the shoots were able to survive. Moreover, 89.3% of them were able to regrow when stored under light conditions. Cryopreservation by vitrif ication was successfully achieved (65.6% regrowth) when shoot tips were precultured on a medium supplemented with 0.4 M sorbitol for 2 d, followed by loading shoot tips with 80% concentrated plant vitrification solution 2 (PVS2) for 20 min; then dehydrated with 100% PVS2 for 60 min at 0°C prior to storage in liquid nitrogen. This procedure is easy to handle and produced a high levels of shoot formation. This protocol could be useful for longterm storage of S. rebaudiana germplasm.Additional key words: cryopreservation; in vitro conservation; micropropagation; osmoticum; root formation. Resumen Propagación clonal y almacenamiento criogénico de la planta medicinal Stevia rebaudianaSe logró con éxito la propagación clonal de Stevia rebaudiana, utilizando microtallos como primer paso para su conservación in vitro. Se obtuvo la proliferación máxima en el medio Murashige y Skoog (MS) suplementado con 1,5 mg L -1 de bencil amino purina y 0,2 mg L -1 de ácido indol-3-butírico (IBA). Las auxinas aumentaron el porcentaje de enraizamiento de los brotes en la concentración de 0,4 mg L -1 de IBA, ácido indol-3-acético o el ácido naftalen acético, pero no se produjo enraizamiento sin regulador del crecimiento vegetal. Se logró una supervivencia del 90% cuando los explantes enraizados fueron aclimatizados in vivo en 1 suelo: 1 perlita: 1 turba. Se almacenaron con éxito brotes de S. rebaudiana in vitro hasta 32 semanas a 24 ± 2°C, en medio MS suplementado con una concentración apropiada de sacarosa, sorbitol o manitol. Después de 32 semanas, el 93,6% de los brotes fueron capaces de sobrevivir y el 89,3% fueron capaces de rebrotar cuando se almacenaron bajo condiciones de luz. Se logró con éxito (65,6% rebrotes) la criopreservación por vitrificación cuando los ápices se pre-cultivaron durante 2 días en un medio suplementado con sorbitol 0,4 M, y a continuación con una solución de vitrificación de la planta 2 (PVS2) al 80% durante 20 minutos, seguido de una deshidratación con PVS2 al 100% durante 60 min a 0°C antes de su almacenamiento en nitrógeno líquido. Este procedimiento es fácil de ejecutar y puede ser...

No abstract

In vitro shoot multiplication of cucumber (Cucumis sativus) was examined from the nodal explants of 10-day-old aseptic plantlets using Murashige and Skoog (MS) media supplemented with different concentration (0, 0.5, 1, 2, 3 mg L -1 ) of cytokinins (6-Benzylaminopurine-BAP, Kinetin-Kn, Thidiazuron-TDZ, and Zeatin). Nodal explants of cucumber showed shoot induction and multiplication in response to all cytokinins tried. MS medium containing Kn was the most effective for inducing shoots from nodal explants of cucumber. The maximum rate of regeneration (83%), the highest number of obtained shoots (7.93 shoots/explant) and the longest shoots (3.61 cm) were obtained on MS medium fortified with 1 mg L -1 Kn. The lowest culture responses were recorded for media supplemented with either BAP or Zeatin. In conclusion, using Kn is strongly recommended than using Zeatin, TDZ and BAP to obtain the highest percentage of regeneration, the highest number of shoot/explant, and the highest shoot length for nodal explants of cucumber.