Recent progress in cassava varietal improvement in China

The paper discusses the research progress mainly for the period of 1990-1993. There are three institutions, SCATC, UCRI and GSCRI, which are systematically working on cassava breeding in China. Since the principal constraint to cassava varietal improvement is the lack of genetic variability, the main approach currently used is the evaluation and selection of hybrid seeds introduced from CIAT/Colombia and from the Thai-CIAT program. In the past few years, remarkable progress has been made in these three institutions, mainly as follows: 1) At SCATC, advanced clones continue to show promising results in comparison with the respectable local control (SC205). Many high-yielding clones were identified in preliminary trials, in which Thai-CIAT material showed a clearly superior performance. 2) At UCRI of the Guangdong Academy of Agric. Sciences, very convincing yield data of a pre-released clone (ZM8002) were obtained from four years of regional trials and another three years of demonstration trials. In addition, many clearly superior new clones were selected from CIAT seed material in a replicated yield trial, nearly doubling the yields of ZM48002 or SC201. Two advanced clones, selected from locally hybridized seeds, showed a high yield potential. 3) At GSCRI, several clones selected from ClAT-introduced seeds showed for the first time a clearly superior yield and dry matter content over local controls in 1992. 4) Additional genetic variability was obtained at SCATC through induced mutations using colchicine treatments. These mutants are presently being evaluate

Recent progress in cassava agronomy research in China

In recent years, cassava agronomy research in China has emphasized soil fertility maintenance, erosion control, planting methods and date of planting and harvesting. The research was conducted in cooperation between the Guangxi Subtropical Crops Research Institute, the South China Academy of Tropical Crops, and the Upland Crops Research Institute with CIAT. Results of three long-term fertility trials indicate that fertilizer application markedly increased cassava root yields. But different varieties showed a different response to fertilizers. SC205 was more responsive to fertilizer application than SC201 or SC124; high rates of fertilizers resulted in high yields of SC205, but not of SC201 or SCI 24. The experiments also showed that during four cropping cycles of cassava in southern China, N was the most important nutrient for increasing cassava root yields, but that K and in some cases P also became increasingly important. Application of farm yard manure or burned soil, in addition to medium levels of chemical fertilizers, had no significant effect on increasing cassava root yields. Experiments on soil erosion control conducted in Hainan and Guangxi showed that contour ridging, intercropping with peanut, or barrier strips of Brachiaria pasture were the most effective practices for reducing soil erosion when planting cassava. Intercropping of cassava with peanut or cassava with seed watermelon increased income more than 65-200% compared with cassava monoculture. Cassava grown with Stylosanthes guianensis barriers reduced soil erosion 14-27%, while increasing income 23-43%. Among several methods of planting cassava, vertical planting resulted in more rapid sprouting than horizontal or inclined planting, especially during periods of drought, but root yields were not significantly different. Among planting on the flat, or on single-row or double-row ridges, there was not much difference in germination and root yield. Research to determine the optimum time of planting and harvest of cassava, conducted at SCATC, showed that when cassava was harvested at 8 months after planting, highest yields were obtained when cassava was planted during the spring (Feb- May); however, when cassava was harvested at 12 months, time of planting had no consistent effect on yield