Optimisation of Somatic Embryogenesis in Cassava

Abstract

Somatic embryogenesis, an efficient regeneration system that is being used successfully in genetic transformation, can be coupled with mutation induction to breed for cassava varieties with desired traits. The embryogenesis system requires the initiation of totipotent cells which can be used as targets for mutagenic treatments. However, initiation of these totipotent cells is low, highly genotypic dependent and has low plant conversion rate. Thus, for its successful application in mutation induction, the system needs to be optimised to overcome these drawbacks. To optimise the system, totipotent cells are initiated on embryo initiation medium (EIM) which consisted of Murashige and Skoog (Physiol Plant 15:473-497, 1962) basal salts supplemented with picloram and 2,4-dichlorophenoxy acetic acid (2,4-D) to produce callus. After 21 days, calli produced are cultured for embryo maturation on maturation medium (EMM) or can also be treated with mutagenic agents for mutant induction. The resulting primary embryos are recycled three consecutive times, each by fragmentation of the cotyledons followed by culture on embryo initiation medium to produce more matured embryos. Somatic embryos produced are then successfully converted into plants by abscisic acid pretreatment in embryo maturation medium or by air desiccation under the laminar flow hood. The methodology described offers optimised, reproducible procedures of somatic embryogenesis for its incorporation into mutation breeding programmes in cassava.

Somatic embryogenesis in two cassava (Manihot esculenta Crantz) genotypes

“…In vitro regeneration through somatic embryogenesis could be useful for genetic manipulation (Elegba et al, 2021) and genome editing (Odipio et al, 2017). Somatic embryogenesis in cassava has been reported previously (Danso and Ford-Lloyd, 2002;Rossin and Rey, 2011;Ma et al, 2015;Mongomake et al, 2015;Raemakers et al, 2006;Danso and Elegba, 2017;Susanti et al, 2017;Pais, 2019). However, it is observed that somatic embryogenesis in cassava is affected by many factors such as source of explant, medium composition, culture environment, and molecules secreted by plant into medium (Nic-can et al, 2015).…”

“…Cassava genotypes UJ-3 and BW-1 are most preferred genotypes and widely planted by Indonesian farmers, especially in the province of Lampung (Sholihin, 2021), nonetheless the reports are scanty on somatic embryogenesis for these genotypes. Another factor which affects somatic embryogenesis in cassava is plant growth regulators (PGRs), and picloram has been reported as the best growth regulator used for inducing somatic embryo in cassava besides 2,4dichlorophenoxyacetic acid (2,4-D) (Mongomake et al, 2015;Danso and Elegba, 2017;Susanti et al, 2017).…”

Micropropagation of Cassava (Manihot esculenta Crantz): Review

“…This approach serves as a significant experimental model for studying the processes of plant embryogenesis and is also one of the best methods for mass multiplication of elite or genetically modified plants [61]. Somatic embryos can be initiated directly or indirectly via a callus phase intervention [62]. The first somatic embryogenesis study in cassava had published in 1982 [63].…”

“…The first somatic embryogenesis study in cassava had published in 1982 [63]. Even though various procedures for inducing somatic embryogenesis have been established, responses to somatic embryogenesis vary considerably among genotypes [64,62], and it is also impacted by explant type and culture medium composition. Somatic embryogenesis in cassava begins with the induction of primary embryos from the explants by culturing on MS medium supplemented with auxins.…”

“…The induced embryogenic calli contain globular embryos that develop to the cotyledonary stage on embryo maturation medium, a cytokinin (0.1 mg/L BAP) [68,69]. In micropropagation, cyclic embryogenesis could increase the frequency of embryo multiplication by a repeated subculture of matured embryos that are allowed to develop into organized somatic embryos for conversion into plants [62].…”