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can produce in degraded soils, and offers resistance to its most important diseases and pests. It is naturally Cassava (Manihot esculenta Crantz) is an important commodity tolerant to acidic soils and offers the convenient flexibilfor industrial processes in tropical countries as one of the few alternaity to be harvested when the farmers need it. Cassava tives to compete with imported maize (Zea mays L.). To maintain has benefited by technological inputs in the area of this competitiveness, cassava breeding needs to be as efficient as possible. This study provides one of the first attempts to produce breeding (Kawano et al., 1998;Kawano, 2003) to sucquantitative genetic data to aid breeding efficiency, through the analycessfully satisfy the needs of farmers and processors. sis of a diallel set among nine parental clones adapted to the midalti-The general scheme for cassava breeding is indeed a tude valleys environment. Thirty clones represented each F 1 cross phenotypic masal selection. Large numbers of segregat-(with three exceptions). Evaluations were conducted in two coning genotypes is evaluated in a lengthy process that retrasting environments with three replications in each location. The quires as many as 6 yr for completion (Jennings and specific combining ability (SCA) effects were relatively more impor-Iglesias, 2002). Individual genotypes (clones) are setant than general combining ability (GCA) effects for root yield. In lected and then multiplied to take advantage of the the case of harvest index, dry matter content (DMC) and plant type vegetative propagation of the crop. architecture GCA effects were about twice as large as those from Little progress in understanding the inheritance of SCA effects. Reaction to mites (Mononychellus tanajoa Bondar) and white flies (Aleurotrachelus socialis Bondar) (based on single-Aé reo 6713, Cali, Colombia. H. Ceballos, also Univ. Nacional de from these 30 plants were obtained. Minor selection was un-Colombia, Carrera 32, Chapinero vía Candelaria, Palmira, Colombia. avoidable at this stage based on the capacity of the botanical Received 21 May 2004. Crop Breeding, Genetics & Cytology. *Correseeds to produce vigorous seedlings and plants capable of sponding author (h.ceballos@cgiar.org).producing six good quality vegetative cuttings.

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Cassava is an interesting crop because its vegetative propagation allows the estimation of within-family ge-Little is known about the inheritance of agronomic traits in cassava netic variation and, indirectly, the relative importance (Manihot esculenta Crantz). The vegetative multiplication of cassava allows cloning of individual genotypes, and separates environmental of epistatic effects. Genetic studies analyzing the imporfrom genetic variation in the within-family variation. Knowing the tance of epistatic effects are not very common, particumagnitude of between-and within-family variation is important for larly in annual crops. Adequate measurement of epidefining breeding strategies and for measuring different components static effects for complex traits, such as yield, is difficult of genetic variances, particularly the seldom-estimated epistasis. A and expensive. Reports on the relevance of epistasis are group of nine genotypes, adapted to midaltitude environments, was infrequent and have generally taken advantage of the used for a diallel study. Thirty clones were obtained from every F 1 cross vegetative multiplication that some species offer (Com-(each clone was represented by six plants), and planted in three replistock et al. , 1958;Stonecypher and McCullough, 1986; cations at two locations. Statistical differences among crosses were Foster and Shaw, 1988;Rö nnberg-Wä stljung et al., 1994; found for fresh-root yield, harvest index, root dry-matter content, and

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.