2. THE SELECTION OF CASSAVA DOUBLED HAPLOID (DH) LINES DERIVED FROM CIAT

The objectives of further genetic improvement of cassava varieties in Vietnam from 2001 to 2010 are: 1) to increase the yield potential and starch content, and enhance early harvestability; 2) to improve eating quality and the nutritional value, especially the carotene and micronutrient content of cassava. This can be achieved through an effective integration of advanced biotechnology techniques and conventional breeding methods. The aims of the 2006-2010 period are: 1) to increase the growing area of KM94 and other promising varieties up to 350 thousand hectares, or close to 60-75% of the total cassava area in the country; 2) to select and release 1-2 new varieties with high-yield capacity of 35-40 t/ha, a starch content of 27-30%, a growing period of 8-10 months, erect stems, short internodes, less branching, compact canopy, uniform root size, white root flesh and suitable for industrial processing; 3) to select short-duration varieties of high quality, suitable for fresh human consumption and animal feeds.

The introduce and development of cassava doubled haploid (DH) plants from CIAT could become an important tool to support hybrid cassava breeding (Zaida Letini, Hernan Ceballos 2003; Hernan Ceballos et al. 2007a. Hernan Ceballos et al. 2007b). Some promising doubled haploid (DH) lines were made, evaluated and test crossed in the field. In the 2001-2007 period, a total of 24,073 sexual seed, new hybrid cassava elite clones from CIAT and 37,210 hybrid seeds from 9-15 cross combinations in Vietnam, 38 breeders’ varieties (from Thailand, Colombia/CIAT, Brazil, China, India, Indonesia, Malaysia, Vietnam), 31 local farmers’ varieties, were planted at Hung Loc Center and Nong Lam University. Of these, 344 accessions of cassava were selected, maintained, and evaluated for priority traits (Table 7). Results of the selection, 98 cassava varieties were the best. KM140 is a supplementary variety for main variety KM94 in order to extend harvesting time, which are now ready for release (Hoang Kim, Nguyen Phuong, Tran Cong Khanh, Hernan Ceballos et al. 2008, http://cassavaviet.blogspot.com/)




Cassava variety KM140 is a hybrid selected from KM98-1 x KM 36 cross in 1998. Thirty cassava comparison experiments and two experiments for determining the best harvesting time of some cassava cultivars were carried out. On red soil in South East region, experiments were planted at beginning of rainy season and harvested after planting from 6,7,8,9,10,11 and 12 months. On grey soil, planted at beginning rainy season and harvested after 10,11 and 12 months.






The data revealed that KM140 has fresh root yield of 33.4 – 35.0 ton/ha, starch content of 26.1 -28.5%, starch yield of 9.5 – 10.0 ton/ha; better than that of KM94. Content of HCN in KM140 is 105.9 mg/kg dry matter, it can be used as fresh consumption, lower than that of KM94; its harvest index was 65%, good resistance to pests and diseases. KM140 is now playing an important role in cassava production in South East and Central Coastal regions, Central Highlands and the mountainous areas in the North (Tran Cong Khanh, Hoang Kim, Vo Van Tuan, Nguyen Huu Hy, Dao Huy Chien, Pham Van Bien, Reinhardt Howeler and Hernan Ceballos 2007)



In South East region, planting at middle of rainy season and harvesting 10 months later revealed that all cassava cultivars gave low starch content (16.6%-22.5%). If harvested 11 months after planting, almost cultivars had starch content around 25% satisfying the requirement of processors. If harvested 12 months after planting most of the cultivars gave good fresh root yield and starch content, but this would cause inconveniences for next crop cultivation. Planting at beginning rainy season and harvesting at 7,8 and 9 months after, KM140 gave fresh root yields of 23.5, 26.7 and 28.7 ton/ha, respectively, equal to that of KM94. Starch content of KM140 harvested 8 months after planting was 28.4% higher than that of KM94 (26.2%), with signnificant difference .