In vitro conservation of taro (Colocasia spp.); a crop with immense potential.
Author: Dr. Vartika Srivastava

Taro, the ancient food crop, belonging to the family Araceae, is one of the most popular food cum-vegetable crops of humid-tropical and sub-tropical zones of the world. This crop has wide adaptability for soil and weather conditions and subsequently fits well in most of the cropping systems adopted worldwide. Taro is identified as an environment friendly crop withstanding well in harsh conditions wherein other crops fail to grow. It is highly productive (15-20 t/ha), short duration and shade loving thereby fits as a profitable inter-crop. The yield of this crop includes corms in addition to the edible leafy portion. Due to extensive vegetative propagation, this crop faces the threat of genetic erosion. The narrow genetic base renders the crop vulnerable to various biotic and abiotic stresses. Owing to its immense potentials as a future crop and the threat of loosing the diversity, the conservation of taro genetic resources for food, nutrition and livelihood is of immense importance.

Conservation strategy:

Conservation strategies involving in situ and ex situ approaches are complementary and the choice depends up on the nature of the material to be conserved. The in situ approach for conserving taro genetic resources in its natural habitat is a good strategy, but it is always facing threat of environmental and demographic variations, habitat loss, pest and diseases. In such circumstances, the ex situ method of conservation in genebank is the best alternative to conserve the diversity. The ex situ conservation methods require specialized germplasm storage facilities which are cost intensive and are at high risk of loss if maintained at only one location, although, it offers a safe escape from the prevailing threats to biodiversity viz., climate change, population growth, cultural change etc.

The ex situ conservation includes field genebanks, seed genebank or cryogenebank and in vitro repository or genebank. Each technology has to be selected based on its merits and utility, security, complementarity and advantages over the other available techniques. In case of vegetatively propagated species, the in vitro conservation approach and further cryopreservation are the best suited approaches for medium term storage and long term storage respectively.

Conservation protocol of taro for medium term storage under in vitro conditions:

The tissue culture technology, in combination with meristem culture, thermotherapy and cryotherapy are being utilized at NBPGR for conservation of a number of vegetatively propagated species, their wild relatives and elite types for further utilization through optimization of conservation and retrieval protocols.

Taro is one of the important vegetatively propagated tuber crops, which is being maintained in the in vitro gene bank (IVGB) of NBPGR for over two decades. A vast diversity of taro germplasm has been collected and conserved at in vitro repository of NBPGR. Cultures are maintained in two sets one in multiplication and one in medium term storage conditions. The medium term storage conditions mainly emphasize on the slow growth of the cultures resulting in extended sub culturing duration.

Plant material and micro-propagation

For in vitro conservation of taro at NBPGR, two approaches were use to extend the subculture duration. One approach is to reduce the growth of the plantlets conserved in vitro through reduced doses of growth regulators and other is to induce corms in vitro. The first approach of reduced growth rate of plantlets is achieved through isolation of shoot tip explants and subculture at 3 months intervals on Murashige and Skoog (1962) semi-solid medium (7 g l−1 agar) with sucrose (3%) as the carbon source, BAP (0.5 mgL-1) and NAA (0.1 mgL-1) as plant growth regulators. For in vitro corm induction, the cultures of Taro (Colocasia sp.) are cultured in Murashige and Skoog’s (MS) medium supplemented with 6% sucrose with BAP (2mgL -1) and 0.1 mgL-1 NAA. The cultures were maintained in a growth chamber at 25±2°C with a 16-h photoperiod, and a photosynthetic photon flux of 30 µmol m−2 s −1 provided by cool white fluorescent lights. The cultures maintained in these conditions produce only single shoot along with a micro-corm and the growth is restricted to extend the subculture till 12-15 months. These in vitro induced corms were then transferred to the pots after 12-15 months of conservation period and successful survival was achieved. Thus, the in vitro derived corms can be utilized for conservation, safe germplasm exchange and as good quality planting material of taro and many other vegetatively propagated crops for the farmers. The in vitro conservation technology aids in maintenance and conservation of germplasm resources to be utilized by farmers and future generation

About Author / Additional Info:
Currently working as Scientist in Tissue Culture and Cryopreservation Unit of ICAR-NBPGR