Optimization of in vitro Cultural Conditions of Haworthia (Haworthia Cooperi Baker)

Haworthia cooperi is a type of ornamental succulent that is propagated by separating the offsets and leaf cuttings. Due to the small number of produced offsets by the mother plant, the rate of propagation in this way is low, so micropropagation can be considered as an effective and efficient way to propagate this ornamental plant.

For this purpose, in the present study, the growth response of Haworthia cooperi plants to in vitro culture conditions in 1398 in the research laboratory of the Department of Ornamental Plants Biotechnology was investigated. This research was conducted in the form of three separate experiments based on a completely randomized design with three replications. In the first experiment, the effects of cytokinin type (BA and KIN) and concentration of cytokinin (0, 1, 2 and 3 mg/l) on leaf explant regeneration were evaluated. In the second experiment, the effects of culture medium type (MS and B5) and concentration of culture medium (0.5 and 1) on plantlet propagation were investigated. In the third experiment, plantlet rooting rate was evaluated under the influence of auxin type (NAA, IBA and IAA) and concentration (0, 0.5, 1 and 1.5 mg/l) of auxin.

The results showed that application of BA and KIN hormones increased the number of regenerated plantlets. The highest number of plantlets (5.50) was recorded in the MS medium containing 3 mg/l BA with 0.5 mg/l NAA. Plantlets cultured in the hormone-free culture medium had no regenerated symptoms. The number of plantlets increased with increasing the concentration of both hormones, but BA hormone in the culture medium had a greater effect on this factor. Lack of cytokinin hormone application in culture medium led to root production; however, the use of BA and KIN hormones in the culture medium reduced the number of produced roots by plantlets. The highest number of roots was recorded in hormone-free culture medium and the lowest number was recorded in the high concentration of BA hormone. The reduction in the number of roots in the culture medium containing BA was greater than the culture medium containing KIN. The of the second experiment revealed that use of MS culture medium showed better performance compared to B5 culture medium. Thus, the highest dry weight of plantlet and roots was obtained at full concentration of MS culture medium. The results of rooting stage showed that the presence of NAA hormone in the culture medium increased rooting in the plant. However, the produced roots in this culture medium were so thick that these roots are not suitable for plant growth in the acclimation stage. Therefore, considering the number and length of produced roots, the optimal culture medium for plantlet rooting is ½ MS culture medium containing 1 mg/l IAA hormone. Determining the best type of culture medium and optimizing it for regeneration, proliferation and rooting is one of the important factors in success in vitro culture conditions. Based on the results of the current study, application of MS medium containing 3 mg/l BA with 0.5 mg/l NAA was so effective for regeneration phase of this ornamental plant. Also, the efficiency of MS culture medium in the process of propagation of this plant is most likely related to the suitability of the components of this culture medium. In general, due to the presence of plant growth regulators such as NAA, IBA and IAA in the culture medium, rooting is induced in plantlets. In the present study, the use of IAA hormone at a concentration of 1 mg/l was a suitable hormonal combination for rooting in this ornamental plant.

Based on the results of the present study, the application of MS culture medium containing 3 mg/l BA with 0.5 mg/l NAA is recommended for regeneration and proliferation of tissue culture plantlets of Haworthia cooperi. It is also recommended to use ½ MS culture medium containing 1 mg/l of IAA hormone for rooting of tissue culture plantlets.