Ex situ Conservation Using In vitro Methods of an Endangered Plant Sterculia urens Roxb.: A High Volume Trade Plant for Gum Karaya

Abstract

Sterculia urens is a vanishing non timber tree species of India, known for its gum exudates having high worldwide trade value and hence needs to be protected for its sustainable supply in nature. In present research, an efficient regeneration protocol is standardized using cotyledonary node of Sterculia urens (Gum Karaya) seedlings. In addition, appearance of different anomalies such as high callogenesis, yellowing of leaves, translucent shoots, shoot etiolation, reduced leaf number, and leaf abscission was observed during the study. Thus based on the assumption that these abnormalities can be a result of ethylene accretion, effect of silver nitrate (AgNO3; ethylene inhibitor) to overcome such abnormalities and enhancement of shoot quality was studied. Among different media compositions tried, full strength Murashige & Skoog (MS) medium supplemented with 0.33 mg/L thiadiazuron (TDZ), was found to be optimum resulting highest shoot multiplication (19.62 ± 0.27) after five weeks incubation with 81.9% regeneration response recorded. After mass regeneration shoots were transferred to full strength MS medium fortified with 0.2 mg/L N6-Benzyladenine (BAP), 1.5 mg/L 6-furfurylaminopurine (Kn), and 2.0 mg/L gibberellic acid (GA3) in combination, which resulted optimum shoot elongation (5.06 ± 0.41 cm) within 2 weeks. Treatments, AgNO3 (1.0 mg/L) with Kn (1.0 mg/L) in MS medium gave adequate shoot quality having dark green & shiny leaves, strengthened stem (dark green), reduced inter-nodal length (de-etiolation) and reduced callus formation. The optimum rhizogenesis (5.67 ± 0.58) was obtained on half strength MS fortified with IBA (2.0 mg/L) when shoots were given pulse treatment using IBA (200 mg/L) for 3-4 min. Further, process of biotization at hardening stage using Glomus sp. enhanced the plant survival rate (80%) at acclimatization stage. Mycorrhizae treated plants were healthy dark green in color having improved root system and less susceptibility to infections in comparison to untreated plants. Tissue culture raised plants revealed 95% genetic homogeneity through Jaccard’s silmilarity coefficient using RAPD markers. The established protocol can significantly be used to generate quality plantlets in elevated amounts to overcome declining abundance of S. urens in natural environment.