Effects of type of explant and age, plant growth regulators and medium strength on somatic embryogenesis and plant regeneration in Eucalyptus camaldulensis

Abstract

Plant regeneration was achieved through direct and indirect somatic embryogenesis in Eucalyptus camaldulensis. Callus was induced from mature zygotic embryos and from cotyledon explants collected from 10, 15, 25, and 30-day-old seedlings cultured on Murashige and Skoog (MS) basal medium supplemented with different concentrations of naphthaleneacetic acid (NAA). Maximum callus induction from mature zygotic embryos was obtained on MS basal medium containing 1 mg l−1 NAA. The frequency of callus development varied based on the age of the cotyledon explants 10-day-old explants giving highest percentage on MS basal medium supplemented with 1 mg l−1 NAA. Callus obtained from mature zygotic embryos gave highest frequency of somatic embryogenesis on MS basal medium containing 0.5 mg l−1 benzyladenine (BA) and 0.1 mg l−1 NAA. Separate age wise culture of the calli, obtained from cotyledons of different ages cultured separately, revealed high somatic embryogenic potential on callus from 10-day-old cotyledons. Direct somatic embryogenesis too was obtained from hypocotyl explants without an intervening callus phase on MS basal medium containing 0.5 mg l−1 BA. The effects of abscisic acid (ABA), sucrose, and different strengths of MS medium on somatic embryo maturation and germination were also investigated. Number of mature somatic embryos increased with lower concentrations (0–1 mg l−1) of ABA while no significant differences were observed at higher concentrations (2–5 mg l−1) of ABA. Compared to basal medium containing lower concentrations of sucrose (1%), the MS medium supplemented with higher levels of sucrose (4%) showed significantly lower frequency of mature somatic embryos. Basal medium without any dilution gave the highest number of immature embryos. However, the number of mature embryos was high at higher medium dilutions.