Progress in cassava breeding at the Chinese Academy of Tropical and Agric. Sciences (CATAS)

During the past 16 years the Chinese Academy of Tropical and Agricultural Sciences (CATAS) has made good progress in developing improved cassava varieties for China. Several improved varieties have been released in south China, of which cv. SC124, with high yield and good cold resistance, is already being planted on a large scale, mainly in Guangxi and Yunnan provinces. SC8002, which is characterized by a high yield potential and tolerance to cold, has mainly been released in Guangdong province, while SC8013, with high yield and good wind resistance, is being multiplied for planting in the typhoon affected areas of Hainan and Zhanjiang district of Guangdong. The release of these new varieties will improve the present situation of dependence on only two varieties, and will promote varietal comparisons, as well as stimulate the development of cassava production in China. In recent years, a large F population and its progeny clones have been produced from true seeds, which were mainly introduced from CIAT/Colombia and from the Thai-CIAT program. Up to 1995, a series of breeding materials with different characters have been evaluated and selected; out of these, three new varieties have been released, more than 30 accessions have been used as cross parents, and 15 promising clones have been recommended for testing in Regional Trials. In 1996, 316 clones were tested at the Single-row Trial, 63 clones were further evaluated at the Preliminary Yield Trial, and 54 clones were included in the Advanced Yield Trials. Most of the clones in the Regional Trial and the Advanced Yield Trial were characterized by high yield and high dry matter content (especially clones OMR33-10-4 and OMR34-1 1-3 have very high dry matter content); their performance at the later stages is closely being watched. Also, some good clones were selected from the Preliminary Yield Trial in 1995/96, such as ZM9315, ZM93255, ZM9317,ZM93236 etc., andOMR36-63-6,OMR36-40-9,OMR36-05-9 etc. from the Single-row Trial; these showed significantly higher yields compared with the check variety, SC205, while their root dry matter contents were higher than 40%, the harvest indices were over 0.62 and they had good wind resistance. High-yield, high dry matter content and good wind resistance are still our major objectives in cassava breeding. From our experience we are convinced that it is impossible to make any major breakthrough in our breeding program by just using our native genetic resources. There are two ways for us to realize our objectives in the future: 1) selection from the hybridizations between our local germplasm and those from CIAT/Colombia or the Thai-CIAT program, such as ZM9036, ZM8803, ZM9057 etc.; and 2) the comprehensive evaluation and direct selection of the seed materials introduced from CIAT/Colombia or the Thai-CIAT program. While the importance of the former scheme is increasing, up to now, many of the good clones with high yield, high dry matter content and high harvest index were selected from this latter source. As such, the materials introduced from CIAT/Colombia or the Thai-CIAT program and their hybrids with the local genetic materials are playing an important role in cassava varietal improvement in China.