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

Abstract

<p style="text-align: justify;"><strong>Aim</strong>: To optimize the concentrations of growth regulators in the media for the proficient micropropagation of grapevine (<em>Vitis vinifera </em>L.) cv. King’s Ruby.</p><p style="text-align: justify;"><strong>Methods and results</strong>: Apical meristems of the grape cultivar were used to establish <em>in vitro</em> shoot cultures. Nodal explants, each containing an axillary bud, taken from <em>in vitro</em> 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 (GA<sub>3</sub>). 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<sup>-1</sup> BAP and 0.1 mg L<sup>-1</sup> GA<sub>3</sub>. Calluses were induced from leaf explants taken from <em>in vitro</em> grown shoots. Callus induction was greater (73.00%) on the medium containing 2.0 mg L<sup>-1</sup> 2,4-dichlorophenoxyacetic acid (2,4-D), 0.3 mg L<sup>-1</sup> BAP and 0.2 mg L<sup>-1</sup> α-naphthaleneacetic acid (NAA). The maximum frequency of shoot regeneration (53.33%) was achieved on the medium supplemented with 1.5 mg L<sup>-1</sup> BAP and 0.5 mg L<sup>-1</sup> NAA, and the regenerated shoots successfully formed roots on growth regulator-free half strength MS medium.</p><p style="text-align: justify;"><strong>Conclusion</strong>: Optimizing the concentration of BAP and GA<sub>3</sub> 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 <em>in vitro</em> 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<sup>-1</sup>, respectively). Finally, we suggest the half strength MS medium that is free from growth regulators for the root formation of the regenerated shoots.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: 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 <em>in vitro</em> shoot cultures, callus induction and shoot regeneration and, hence, to propagate disease-free true to type grape cultivars in a short time.</p>