The current study indicates that hormone treatment (IBA & IAA) is the favourable and best option for the conservation and vegetative propagation of Himalayan yew. As our study depicts and recommends IBA the best rooting hormones in comparison to the Indole acitic acid ( IAA). In fact, the auxins application is important to produce roots in fresh stem cuttings as they have been experienced for stimulating secondary plant growth that results in the reserve food material mobilization to the root initiation site (31). Auxins application increases rooting and quality of roots in various tree species (32). It is a well-documented that the auxins application is important for the roots formation in the cuttings of plant stem as they have been found in stimulating the cambial activity which results in reserve food mobilization to the root initiation site (31; 33).
Also, a successful rooting in juvenile shoot cuttings of T. wallichiana with different auxins has been documented from the other temperate areas as well (34, 35, 36, 38, 39)
Our results are also similar with Nautiyal et al. (1991) (40), who treated hormones on stem cutting of teak for roots induction and concluded that IBA is the favourable and best auxins. Other scientists (41, 44, 37, 42, 45, 46, 43) also documented that the IBA application play a vital role in the propagation of stem cuttings of Taxus. Their results clearly mentioned that vegetative propagation (in-situ conservation) can improve the number of juvenile’s plants of genus Taxus.
Several primary root formations under the influence of IBA application have been obtained in the present trials (7000 ppm). It must be accepted that a higher root to shoot is satisfactory for achieving a higher survival rate after transplantation of field. It has also been reported that more than optimums concentration of auxins is toxic to the root regeneration, while theoptimum concentration of hormones is favorable (47, 48). In our study we had applied the maximum concentration of 7000 ppm of both the auxins (IBA and IAA) which shows favourable response to the growth of T. wallichiana cuttings.
The differential response to changing concentrations of hormones for survivals of T. wallichiana were noted in the present study could be like the action of increasing Auxins (2000 ppm – 7000 ppm). The IBA application may have an indirect effect by increasing the translocation speed and the movement of sugar to the cuttings base which in result stimulate rooting (31).
IBA application in the current study significantly increased the survival percentage (number of roots, length of roots, number of leaves, and number of sprouts). Same results were obtained in another study by applying different hormones, for the initiation of a maximum rooting percentage in the juvenile fresh stem cuttings of T. wallichiana; IBA is the effective and best hormone (50). It is now decided that IBA is the best rooting auxins for Taxus species and it was confirmed by many workers (36, 29). The time duration of our study was kept 20 weeks after the plantation of the cutting of T. wallichiana. Similarly, the auxins effect on growth and induction of adventitious roots of T. wallichiana cuttings after 4 and ½ months of application/treatment and plant growing. In general, it has been found that among various auxins IBA was the more active for root germination showed the maximum percentage of survival, rooting percentage, percentage of callusing roots per cutting, and length of root per cutting (37, 41, 42, 43, 45, 46). The researcher studied the application of 1000 ppm and 500 ppm of IBA on the T. wallichiana cuttings and found, IBA 500 ppm showed slightly less response than IBA 1000 ppm. IBA 1000 ppm showed the best rooting response on shoot cuttings of T. wallichiana in the spring season with a rooting percentage (95%) compared to other treatments in other seasons (51). In our study the best response was given by 7000 ppm in case of both IBA and IAA. By looking into other studies, it clears that by increasing the concentration up to 7000 ppm the growth will be high.
By using IBA, with some other cultivar of yew (49) that showed that treatment of hormone was very important for successful conservation and propagation of T. wallichiana. By the treatment of hormones, stem cuttings of some other species were also published (55), their research showed that the best response for rooting due to IBA followed by IAA and NAA in rooting percentage, the cuttings heights, number of roots per cutting in Sage, Rosemary, and Elderberry. Similarly, the treatments of auxins (IBA, IAA, and NAA) on the root development were studied in species like Melissa officinalis (52), Ficus Benjamina (53), and Oryza sativa (54).
Auxins are involved in the formation of root, cambial cells activation, and lateral bud inhibition. They have been found as naturally existing compounds that promotes the formation of root and synthetic auxins also stimulating the emergence of root on cuttings. It is well documented and verified maximum time that auxins applied (naturally or artificially) is needed for adventitious root initiation on stem cuttings. Initial cells division of roots is dependent on either endogenous or applied auxins (56).
Our findings are also in similarity with (57) that showed that root development in stem cuttings of T. wallichiana using IBA followed by IAA and NAA and in control where no auxins treatment was given, less root formation was observed in those cuttings, and the lowest survival was found during the observation of cuttings. In this case further the survival becomes very difficult and ultimately the cuttings died. In this respect, our results are similar as obtained by (58).
Thus, our study suggests the utilization of auxins mainly IBA for regeneration of T. wallichiana under natural conditions. The results of our research will be beneficial for developing propagation protocol of T. wallichiana species especially for the moist temperate climate of the Himalayan Region.