In vitro callus induction and plantlet regeneration is influenced by the maturity status of embryos of Brassica rapa varieties

Abstract

Brassica rapa (AA, 2n = 20) is a prime oilseed species in Bangladesh that can be improved via biotechnological approaches. Rescue of developing embryos after an interspecific hybridization, which otherwise usually tend to abort, is very important for improvement of this species, that require an efficient embryo culture protocol. The immature torpedo shaped embryos (451-700 µm) and mature walking-stick type (>700 µm) embryos of five B. rapa varieties namely, Safal, Agrani, BINA Sarisha-6, BARI Sarisha-6, BARI Sarisha-15 were cultured in basal MS media supplemented with 1 mgL-1 BAP, 0.5 mgL-1 NAA & 1 mgL-1 2,4-D. The immature embryo culture followed indirect somatic embryogenesis process but the mature embryos followed direct organogenesis. The immature embryos induced callus within 11-15 days whereas the mature embryos regenerated plantlets through direct organogenesis within 8-11 days. The varieties Agrani, BARI Sarisha-6 and BINA Sarisha-6 induced the highest percentages of callus from immature embryos and the varieties Safal and BARI Sarisha-15 regenerated the highest percentage of plantlet from mature embryos. Safal and Agrani induced callus and regenerated plantlets comparatively earlier than other varieties. An increase in the concentration of BAP from 10 to 20 ppm in MS media + 5 ppm IBA decreased the size of the plantlets of all varieties except the Agrani. The data could be used in improving the existing embryo rescue protocols. The direct organogenesis process of mature embryos can potentially shorten the breeding cycles.

Prospects of Embryo Rescue in Developing Novel Brassica Genotypes

“…Varietal variation also interacted to both success and response to embryonic development in both mature and immature embryo culture. For example, some Bangladeshi varieties of rapeseed (e.g., Agrani, BINA Sarisha-6 and BARI Sarisha-6) produced a greater percentage of calli compared to other varieties in similar culture media (Zisan et al 2015). The cotyledonary-shaped embryos (15 DAP) from an interspecific cross of B. rapa and B. oleracea revealed considerably higher rates of plant regeneration.…”

“…However, success in callus induction was also noted from the very young embryos at their globular stages in B. juncea (Liu et al 1993). Mature embryos (> 700 μm) were cultivated from five genotypes of B. rapa species that produced plantlets directly within 7 to 12 days (relatively less time) after inoculation through direct organogenesis (Zisan et al 2015). In an another experiment, the cotyledonary-shaped embryos reached the maximum plant regeneration rates (overall 83.3 percent) and it was around 20 percent higher compared to torpedo-shaped embryos (63.1 percent) (Ripa et al 2020).…”