Survey for genetic resources in tropical rootcrops in relation to drought resistance

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This research was conducted in collaboration with Philippine Root Crop Research and Training Center, Leyte State University to evaluate genotypic variation in cassava and sweetpotato in drought tolerance and to identify the traits that are closely related to the tolerance. In addition to the collection of the Center, we further collected a number of genotypes from several drought-prone areas m the Philippines.Sevearl surveys among the rootcrop growing Canners indicated that the question on decision-making strategies by farmers on sustained adoption of a variety is different from the question of preference to grow a certain variety. The former involves more than just traits preference ; and includes other considerations, such as resources, availability of planting materials, use and market, perceived or actual physical or environmental constraints, etc., which is a subject for futher study.Under water stress, dry matter is a product of water use (WU) and water use efficiency (WUE). Based. on this concept, the growth responses of 28 cassava genotypes and 18 sweelpotato genotypes to water stress were examined in a series of pot experimentsIn cassava, drought significantly reduced dry matter production. Results of a correlation analysis indicate that the genotypic variation in dry matter response to drought was better explained by that in WUE than in WU. In sweetpotato, dry matter production was also significantly reduced in droughted plants. The drought treatment significantly reduced WU, while it scarcely affected WUE. These facts clearly show that the reduction of WU but not WUE caused dry matter reduction, which is opposite to the case of cassava.The results of a series of field experiments generally support those obtained by the pot experiments, which are necessary to validated by the evaluation of Genotype x Environment Interaction in further study.