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A yield evaluation in single‐row plots were made in Colombia of approximately 1,900 accessions of cassava ( Manihot esculenta Crantz), collected throughout Latin America and 4,700 hybrid lines from crosses within the same germplasm. Superior genotypes were selected on the basis of harvest index (proportion of root weight to total plant weight) and root yield in single‐row plots and then evaluated in replicated yield trials under diverse environments. With a rainfall of less than 800 mm well distributed throughout the year on a fertile soil, root dry‐matter yield of 21 metric ton/ha/year (average of top 10 genotypes) was obtained without irrigation or fertilization. Yields of 12 metric ton/ha/year dry matter were obtained without irrigation in a climate with a 5 monthd ry season. Yields of 8 metric ton/ha/year dry matter were obtained on acid oxisols of the tropical savanna, with a moderatef ertilizer application. Several genotypes showedc onsistently superior performanceo ver the wide range of environments, and their yields exceeded those of correspondinglo cal strains by 50 to 150%. These results confirm that cassava is an efficient carbohydrate producer adapted to a wide range of environments, is tolerant of drought and acid soils, and offers a great opportunity for genetic improvement. Present farm yields of 3 to 5 metric ton/ha/year (dry matter) could be increased to 10 to 15 ton/ha/year through simple selection and improved cultural practices. Largescale carbohydratep roductioni n tropical savanna o xisols is possible by planting improved cassava genotypes.
Kawano et al. (Mon,) studied this question.