Response of Different Explants for Callus Induction in Cucumber

In vitro regeneration of cucumber is relatively difficult for genetic improvement. In this regard, different concentrations of growth regulators and three types of explants (cotyledon, hypocotyl and leaf disc) were investigated for their efficiency on callus induction potential. Among different explants explored for callus induction with different concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D), leaf disc responded earlier (4.67 days) and showed higher percentage of callus induction (91.50%) with 2 mg/l 2,4-D supplemented Murashige and Skoog (MS) media. The same concentration of 2,4-D resulted in the maximum callus fresh (0.56 g) and dry weight (0.39 g) from leaf disc explant. Then the callus was transferred to untreated, 2.0 mg/l BAP + 0.2 mg/l NAA + 1.0 mg/l Kn, 2.0 mg/l BAP + 1.0 mg/l NAA + 1.0 mg/l Kn and 2.0 mg/l BAP + 1.5 mg/l NAA + 1.0 mg/l Kn fortified MS medium. After transferring the callus of different explants to shoot regeneration media containing different concentrations of 6-benzylaminopurine (BAP), 1-naphthaleneacetic acid (NAA) and Kinetin (Kn), only cotyledon callus started to regenerate shoot. The combination of BAP (2 mg/l) + NAA (0.2 mg/l) + Kn (1 mg/l) showed highest shoot regeneration percentage (67.77%) and the maximum number of shoots (5.12) per explant were recorded in the treatment combination of 2 mg/l BAP + 0.2 mg/l NAA + 1 mg/l Kn. These results provided a basis for the optimization of the callus induction protocol of cucumber for genetic transformation.