Effect of vermicompost extract with phytohormones on micropropagation and in vitro flower induction of Lindernia minima (Benth.) Mukerjee - an endangered plant species endemic to Tamil Nadu, India

Lindernia minima is an endangered and endemic plant species (Red list data of IUCN). Based on the IUCN threat status and highly restricted distribution, the present research work develops an efficient micropropagation method for its conservation. The present study employed purified vermicompost extract in combination with different concentrations of phytohormones on plant regeneration and in vitro flower induction. The shoot tip explants were cultured on quarter-strength of MS medium (Murashige and Skoog) with different (0.5 – 3.0 mg L⁻¹) concentrations of BA (6-Benzyladenine), KIN (Kinetin), and TDZ (Thidiazuron). Initially, the effect of phytohormones alone produced the lowest results with reference to the percentage of response, number of shoots/explant, and length of the shoots. Hence, the explants were inoculated on a quarter-strength MS medium with various concentrations of phytohormones combined with various percentages (25%, 50%, and 75%) of purified vermicompost extract (VCE). TDZ at 2.5mg L⁻¹ with 50% of VCE produced a high-frequency rate of the shoots. Elongated shoots were transferred into a quarter-strength of MS medium with TDZ (2.5 mg L⁻¹) and 50% of VCE, and fortified with several concentrations of Gibberellins (0.2 – 1mg L⁻¹) for in vitro flower induction. After 4 weeks of culture, the maximum numbers of shoots with well-developed flowers were observed at 2.5 mg L⁻¹ TDZ fortified with 50% VCE and 0.6 mg L⁻¹ of GA₃. Well-elongated in vitro shoots were inoculated onto MS rooting medium with various concentrations of (0.5 – 3 mg L⁻¹) IAA (Indole -3- acetic acid) and IBA (Indole -3- butyric acid). The highest root formation was observed at 2 mg L⁻¹ IBA with a quarter-strength MS medium. After the well-root formation, plants were transferred to the acclimatization process and established with a 95% of survival frequency in the field conditions. The present research revealed that adding purified VCE with phytohormones promoted the high regeneration ability of Lindernia minima from shoot tip explants. So far, in vitro propagation studies are not reported for this plant. Hence, the present investigation will be more useful for mass in vitro clonal propagation of Lindernia minima using shoot tip explants.