Somatic embryogenesis in two cassava (Manihot esculenta Crantz) genotypes

Plant breeding through hybridization in cassava is facing a problem due to inconsistent flowering, and also the donor genes controlling superior traits are limited. An alternative method of breeding is through genetic transformation, and regeneration via somatic embryogenesis is promising route to achieve this. As somatic embryogenesis in cassava is genotype-specific, in the present study a protocol has been developed for UJ-3 and BW-1 genotypes. Immature sterile leaves from 7-10 days axillary shoots in a pre-condition medium were used as an explant. Leaves were inoculated on Murashige and Skoog (MS) medium containing picloram (0.0, 7.5, 10.0, 12.5, and 15.0 mg/L) and 1-naphthalene acetic acid (NAA, 6 mg/L) for induction of somatic embryos (SEs). Genotype BW-1 showed best results as early callus formation time i.e. 8.04 +/- 0.32 days after induction (dai) compared to UJ-3 (8.67 +/- 2.13 dai). The callus fresh weight (0.64 g) was also higher in BW-1 than UJ-3 (0.38 g) after 4 weeks in callus induction medium (CIM), and the callus formation ranges between 85.19 +/- 3.70 to 96.30 +/- 3.70% for both genotypes. Subculturing embryogenic callus to MS+CuSO4 (4 mu M) + picloram (6 mg/L) +NAA (0.5 mg/L) (SK1 medium) germinated maximum SEs in BW-1 (46.56 +/- 36.86), whereas the number was less for UJ-3 (11.89 +/- 11.90). Further, shoots were developed from green cotyledons followed by hardening and acclimatization of plantlets.