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Genetic and environmental variabilities of root dry matter content (RDMC) of cassava ( Manihot esculenta Crantz) clones (accessions and breeding lines) were estimated at different harvest months (8 12 months), seasons (wet and dry), and locations (three altitudes). To assess the possibility of obtaining higher dry matter yield through selection for RDMC, genetic studies based on F 1 variability and parents‐offspring regressions also were conducted. Age of plant, season, and location significantly affected root dry matter content. Temperature appeared to be an important factor related to the effect of location. The highest RDMC was obtained with 8 month‐old plants harvested at the beginning of the dry season in the high altitude location, while the lowest occurred with 12‐month‐old plants harvested at the beginning of the wet season at the low altitude location. The clone effect was highly significant and a broad‐sense heritability of 0.87 was obtained. Clone ✕ location interaction was also significant, but the magnitude of this effect was much smaller than that of the clone effect. Genetic analyses suggested that inheritance of RDMC was controlled mainly by polygenic additive factors. Narrow‐sense heritabilities ranging from 0.51 to 0.67 were obtained. There was no indication of negative response in root dry matter content after intensive mass selection for root fresh yield. The data indicate that RDMC can be increased by simple breeding techniques such as phenotypic mass selection. Selection of clones at one location was largely valid for other locations; however, final selection should be made at each specific location for maximum potential gain.
Kawano et al. (Thu,) studied this question.