Influence of Cytokinin and Auxin Types and Concentrations on In Vitro Shoot and Root Regeneration of Cactus Pear [(Opuntia ficus-indica (L.) Mill.]

Abstract

An experiment was conducted with the aim of developing a protocol for the in vitro propagation of cactus pear from in vitro derived areole explants. The protocol involves subsequent in vitro morphogenesis and rooting of the in vitro proliferated shoots. For the shoot proliferation stage, explants each with 1 to 2 areoles were cultured on Murashige and Skoog medium (MS) supplemented with benzyladenine (BA) and kinetin (Kin) each with concentrations of 0, 0.5, 1.0, 2.0 and 4 mg/l and two combinations (0.5 mg/l BA + 4.0 mg/l Kin and 0.5 mg/l Kin + 4.0 mg/l BA). Analysis of the results indicated that there was no significant difference among the treatments used in terms of percentage of bud formation. Kinetin at 2.0, 1.0 and 0.5 mg/l were the best for days to shoot emergence. The highest bud numbers (95.75 buds per explant) were achieved on medium supplemented with Kin at 1.0 and 2.0 mg/l. Culturing the explants on MS medium amended with Kin at 1.0 mg/l concentration significantly augmented the shootlet proliferation rates to 29.5-fold higher than on MS-free medium. The best result for shoot length (4.7 cm) was obtained from medium with 0.5 mg/l Kin. Similarly, Kin at 0.5, 1.0 mg/l and BA at 2.0 mg/l yielded maximum plant mass production (shoot fresh and dry weight). Elongated shoot cuttings were placed on the medium (0, 0.25, 0.5, 1.0 and 1.5 mg/l) of naphthalene acetic acid (NAA) and indole-3-butyric acid (IBA) and (0.25 mg/l IBA + 1.5 mg/l NAA and 1.5 mg/l IBA + 0.25 mg/l NAA) for in vitro root induction. Hundred percent rooting was achieved on all of the treatments tested in two weeks of culture except the PGR free medium. The most efficient growth treatment for the longest root length (10.75 cm), maximum root fresh weight (1.88 gm) and root dry weight (0.41 gm) was IBA at 1.5 mg/l. However, there was no significance difference between IBA at 1.0 mg/l and IBA at 1.5 mg/l regarding to root length per explant. The best result for root number (10.0 roots per explant) was obtained from medium supplemented with 1.5 mg/l NAA. In conclusion, it is beneficial to use the in vitro protocol developed in this study for mass micropropagation and circumvent the challenges of conventional in vivo multiplication of cactus pear.