In vitro multiplication of Quercus leucotrichophora and Q. glauca: Important Himalayan oaks

Abstract

Multiple shoots of Quercus leucotrichophora L. and Q. glauca Thunb. were induced from the intact embryos (decoated seeds) as well as from the cotyledonary nodes (with attached cotyledons but without radicle and primary shoot) of 3-weeks old in vitro grown seedlings on Woody Plant (WP; Lloyd and McCown, 1980) and Murashige and Skoog (MS; 1962) media supplemented with 6-benzyladenine (BA), either alone or in combination with gibberellic acid (GA₃)/ indole-3-butyric acid (IBA). BA (22.19 μM) was effective for induction of multiple shoots and addition of GA₃ to the medium further enhanced the shoot number and shoot height but resulted in shoot thinness. High frequency shoot multiplication was achieved using cotyledonary nodes. Shoots were further multiplied from the original explant on WP medium supplemented with BA (22.19 μM). Nearly 78% and 67% rooting was obtained in Q. leucotrichophora and Q. glauca microshoots (3–4 cm high), respectively on 1/2 strength WP medium supplemented with IBA (14.76 μM). However, this was associated with basal callus formation. Treatment with IBA (25–100 μM) for 24 or 48 h followed by transfer to PGR free 1/2 strength WP medium not only improved the rooting percentage but also avoided basal callus formation. IBA at 100 μM for 24 h was most effective (90% and 100% rooting in Q. leucotrichophora and Q. glauca, respectively). In vitro rooted plants were hardened and established in garden soil.

Growth performance of 6-month-old in vitro raised plants was compared with ex vitro plants (seedlings) of the same age. The photosynthesis and transpiration rates of eight months old in vitro and ex vitro raised plants of both species were measured under different light (0, 600, 900, 1200, 1500 and 2000 μmol m⁻²s⁻¹) and temperature (20, 25, 30, 35 and 40 °C). Light optimum for photosynthesis was around 2000 μmol m⁻²s⁻¹ in Q. leucotrichophora and around 1500 μmol m⁻²s⁻¹ in Q. glauca whereas optimum temperature for photosynthesis was 25 °C in Q. leucotrichophora and 30 °C in Q. glauca. The rate of transpiration at different temperatures (20–40 °C), in the two species, increased with increase in the light intensity up to the highest level, i.e., 2000 μmol m⁻²s⁻¹. Temperatures beyond 35 °C adversely affected the rate of transpiration in in vitro raised as well as ex vitro plants of both the species. In vitro raised and hardened plants of both the species were comparable to ex vitro plants in terms of gas and water vapour exchange characteristics, within the limits of this study.