Optimizing the concentrations of plant growth regulators for in vitro shoot cultures, callus induction and shoot regeneration from calluses of grapes

Aim: To optimize the concentrations of growth regulators in the media for the proficient micropropagation of grapevine (Vitis vinifera L.) cv. King’s Ruby. Methods and results: Apical meristems of the grape cultivar were used to establish in vitro shoot cultures. Nodal explants, each containing an axillary bud, taken from in vitro grown shoots were inoculated in shoot proliferation medium, i.e., half strength Murashige and Skoog (MS) medium supplemented with benzyl aminopurine (BAP), kinetin, glycine and gibberellic acid (GA3). A higher number of shoots (5.33) with greater shoot length (2.75 cm) was produced in the medium supplemented with 1.0 mg L-1 BAP and 0.1 mg L-1 GA3. Calluses were induced from leaf explants taken from in vitro grown shoots. Callus induction was greater (73.00%) on the medium containing 2.0 mg L-1 2,4-dichlorophenoxyacetic acid (2,4-D), 0.3 mg L-1 BAP and 0.2 mg L-1 α-naphthaleneacetic acid (NAA). The maximum frequency of shoot regeneration (53.33%) was achieved on the medium supplemented with 1.5 mg L-1 BAP and 0.5 mg L-1 NAA, and the regenerated shoots successfully formed roots on growth regulator-free half strength MS medium. Conclusion: Optimizing the concentration of BAP and GA3 and omitting the glycine and kinetin in the culture medium increased the number and length of shoots. Similarly, for inducing the callus of the leaf explants, taken from in vitro grown shoots, it is recommended to adjust the medium with the higher concentration of 2,4-D and lower concentrations of BAP. Moreover, the maximum number of shoots was regenerated on a medium supplemented with relatively high levels of both BAP and NAA (1.5 and 0.5 mg L-1, respectively). Finally, we suggest the half strength MS medium that is free from growth regulators for the root formation of the regenerated shoots. Significance and impact of the study: Optimizing the concentration of growth regulators is crucial for the efficient micropropagation of a grape cultivar. Knowing the specific balance between the growth regulators is necessary to establish in vitro shoot cultures, callus induction and shoot regeneration and, hence, to propagate disease-free true to type grape cultivars in a short time.