Shoot-tips and somatic embryos are the explants of choice for the in vitro long-term storage of ex situ plant genetic resources in liquid nitrogen. Cryopreservation of organized structures has significantly progressed, especially for species of tropical origin, with the development of several vitrificationbased procedures such as encapsulation-dehydration, vitrification and droplet-vitrification approaches. They have allowed improvements in survival and recovery after cryopreservation compared with conventional crystallization-based protocols, proving their effectiveness for large scale application with embryos and shoot-tips of different plants. This review addresses the main physical and technological aspects involved in plant cryopreservation methods, illustrating the development of research with three cases: citrus, cassava and potato. These studies demonstrate how cryopreservation strategies are increasingly applied for their successful employment in the genebanks.

The importance of cassava as the fourth largest source of calories in the world requires that contributions of biotechnology to improving this crop, advances and current challenges, be periodically reviewed. Plant biotechnology offers a wide range of opportunities that can help cassava become a better crop for a constantly changing world. We therefore review the state of knowledge on the current use of biotechnology applied to cassava cultivars and its implications for breeding the crop into the future. The history of the development of the first transgenic cassava plant serves as the basis to explore molecular aspects of somatic embryogenesis and friable embryogenic callus production. We analyze complex plant-pathogen interactions to profit from such knowledge to help cassava fight bacterial diseases and look at candidate genes possibly involved in resistance to viruses and whiteflies—the two most important traits of cassava. The review also covers the analyses of main achievements in transgenic-mediated nutritional improvement and mass production of healthy plants by tissue culture and synthetic seeds. Finally, the perspectives of using genome editing and the challenges associated to climate change for further improving the crop are discussed. During the last 30 yr, great advances have been made in cassava using biotechnology, but they need to scale out of the proof of concept to the fields of cassava growers.

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The lack of good quality planting material of farmers' cassava varieties, produced locally and at low cost, is a major constraint limiting the expansion of cassava production in Colombia. This article describes the adaptation of conventional cassava propagation to a low-input scheme for rural tissue-culture multiplication, developed and run by small, resource-poor farmers (referred in this article as an informalfarmers' seed production system). Developed through a two-phase participatory process by a group of women farmers, a non-governmental organization and International Center for Tropical Agriculture scientists in a farmers' community in the hillsides of southern Colombia, the project resulted in alternative, economical and readily available sources of tissue-culture material and equipment. Rates of multiplication achieved with the system were as high as with conventional tissue-culture procedures.

Cassava is uniquely suited for food security and economic development in unfavored areas of the tropics. Development research for cassava is an urgent need. In 1998, the Cassava Biotechnology Network (CBN) convened a workshop of cassava stakeholder groups in Latin America. After hearing an opening statement from representatives of small-scale cassava producers and processors, stakeholders formulated a consensus set of research and development (R&D) priorities. An adequate supply of good-quality planting material of desired varieties was clearly the most urgent, followed by R&D on market-value traits; yield losses due to pests, diseases, and drought; and cropping system flexibility.Two new projects are using in vitro techniques to address priorities of small-scale cassava farmers in Latin America. One project in Colombia combines a nongovernmental organization, a local farmers' association, and the international research center, CIAT, to explore affordable micropropagation. Findings to date show that most culture medium components can be replaced with local products, and a rustic growth room permits good culture growth without electricity or air conditioning. Low-costs system(s) developed will be assessed as a local microenterprise.A second project, in Ecuador, couples local cassava germplasm (with oral histories and an in vitro back-up collection) and elite clones (introduced in vitro) with new concepts in agribusiness development, to restart local farmers' cooperatives after the disastrous 1998-99 el Nifio floods. The project was developed through group planning by the cooperatives, the local technical university, the national agricultural research program, and CIAT.Research to improve in vitro tools focuses on safe and stable conservation and exchange of cassava genetic resources, long-term, less expensive conservation, rapid clonal propagation, and ultimately, genetic transformation technologies to add desired traits to useful cassava varieties.

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