Micro-propagation of casssava plants through the temporary immersion system and hardening of massive numbers of cassava vitroplants

Tissue culture is a technique widely used for propagation of plant material. This method has been used successfully to propagate species such us cassava, sweet potato, plantain and sugarcane. Recently, the development of techniques such us the Recipient for Automated Temporary Immersion (RATI) and Temporary Immersion System (TIS) have improved significantly the efficiency of tissue culture propagation methods. The RATI and TIS techniques were originally developed in France and have been tested successfully in countries such us Cuba with cassava and other species. The use of these methods is helping research institutions to advance in the production of massive numbers of plants. However, one of the main limitations for a wider use of these techniques is the hardening period during which the explants have to be adapted to normal conditions, before its final transplanting to the production sites. This change of the conditions in which the plants are growing usually causes high death percentages in the plants produced with the in vitro multiplication systems. CLAYUCA, in collaboration with CIAT, has done some work for the development of a methodology for the hardening phase of massive numbers of vitroplants. The present paper describes these experiences, discussing the different stages of a successful methodology developed for handling large numbers of in vitro plants produced with the help of biotechnology-based multiplication systems. INTRODUCTION Important advances have been obtained in recent years in the development of improved, higher yielding cassava varieties. This new cassava germplasm is helping farmers to obtain higher incomes and to improve their economic well-being. Despite the advances obtained in breeding efforts, one of the most important constraints for a more widespread use by farmers of the improved cassava varieties is the lack of planting material, in larger quantities, at the right moment and with the desired quality characteristics. The use of biotechnology-based methods for rapid multiplication of improved varieties is one of the strategies that is helping to solve this limitation. One of the most important biotechnological methods available is the one known as Recipient for Automated Temporary Immersion, more popularly known as the RATI system. With the use of RATI systems for multiplication of cassava planting material, researchers at CIAT have been able to obtain very good multiplication rates, varying between 5 to 10, depending on the variety (Table 1). 1 Executive Director, Latin American and Caribbean Consortium to Support Cassava Research and Development (CLAYUCA). CIAT, Apartado Aereo 67-13, Cali, Colombia. 2 Greenhouses Administrator, CIAT, Apartado Aereo 67-13, Cali, Colombia. 3 Field technician, Latin American and Caribbean Consortium to Support Cassava Research and Development (CLAYUCA). CIAT, Apartado Aereo 67-13, Cali, Colombia.