MICROPROPAGATION AND GERMPLASM CONSERVATION OF TARO : COLOCASIA ESCULENTA VAR. ESCULENTA

Abstract

Axenic cultures of Colocasta esculenta var. esculenta were established from corm axillary bud explants. The rate of successful initiation was 76 percent of total buds cultured and plantlets with well-developed shoot and root systems were obtained after 4 weeks culture on Murashige and Skoog (MS) medium supplemented with 20 gr1 sucrose and solidified with 2.4 gr1 gel rite. High frequency direct shoot regeneration was achieved through enhanced axillary development from conn axillary buds and thin-section-culture of in vitro corms on similar hormone-free medium. ln addition, rapid clonal multiplication of up to 80 shoots per conn in 8 weeks was achieved through thin-section -culture of tissue-cultured-taro corm on medium containing 50 > uM BA. Prolonged culture on high BA media produced up to 120 shoots per culture at the end of 6 months without further subculture. Regenerated shoots developed roots readily when transferred to hormone-free medium. Plantlets were ready for potting in 4 weeks and yielded l00 percent successful acclimatization rate. Calli were initiated in root and thin-section-culture of tissue-cultured corm explants on media containing NAA or 2,4-D, incubated under light or dark conditions. Nodular, yellow, root callus regenerated roots on hormone-free medium. Two types of corm calli were obtained, yellow nodular callus from the periderm and translucent friable callus !rom the central conn tissues. Nodular callus regenerated roots on hormone-free medium but shoots and roots on medium with high BA or sucrose concentrations. Friable callus ·regenerated into complete plantlets on hormone-free medium atop original conn explant. Almost 90 percent of shoot-tip cultures were effectively conserved for up to 12 months without further subculture on half-strength MS medium overlay with water under low light intensity. Over time, all cultures produced roots and developed into complete plantlets. The type of culture seal used had a significant effect on multiple or single shoot formation, possibly due to the extent of gaseous exchange. Paraffin oil overlay was found to be unsuitable and led to early culture necrosis. The presence of BA did not enhance culture survival. In vitro shoot-tip and developing bud explants were successfully encapsulated in an alginate matrix and stored for more than 4 weeks at room temperature or refrigerated at 5"C for 8 weeks with minimal loss of viability. Similarly, m vitro induced corms were also effectively stored for 4 weeks at room temperature or 6 months at 5"C. Both artificial seeds and 111 vitro corms without any culture medium are suitable for use in the exchange of taro germplasm. They can be stored and transported via glass vials or small containers and be planted directly into potting mix or transferred to fresh culture media with minimal loss of regenerability. The developed protocols can be employed for germplasm conservation, exchange and mass propagation for cultivation.