Cassava Germplasm

More than 10 years ago, the Biotechnology Research Unit, together with the Genetic Resources Unit, set goals to develop methods of cryopreservation that would lead to safer, cheaper, and long-term conservation of genetic resources. Methods to cryopreserve cassava germplasm were developed 4 years ago, using classic protocols (chemical dehydration and programmed freezing). Escobar, R.H.; Mafla, G.; Roca, W.M. 1997. A methodology for recovering cassava plants from shoot tips maintained in liquid nitrogen. Plant Cell Reports
16: 474 - 478. New protocols-encapsulation dehydration and quick-freezing-have now been developed and validated with more than 43% of the entire cassava core collection. More than 82% of the accessions tested have recovery rates of more than 30%, the minimum required for cryopreservation. Protocols are now being adjusted for wild relatives of cassava, species of which sometimes behave very poorly in vitro or even in the field, making their conservation troublesome. Plants have been recovered for M. esculenta ssp. flabellifolia, M. esculenta ssp. peruviana and M. carthaginensis.

Cryopreservation is also being used to support transformation of cassava. Developing friable embryogenic callus cell lines is time consuming, with the inherent risks of genetic instability and low plant recovery over time. Cryopreserving FEC cell lines is therefore a viable alternative. FEC cell lines of two cassava cultivars (TMS 60444 and M Col 2215) have been frozen and recovered. Because transformation of cassava requires the development of FEC for each specific cultivar, we expect to build up a cryopreservation bank of FEC cell lines of various cassava cultivars.