Especies silvestres de Manihot: un recurso valioso.
1990
Chavez R.
Ninety-five wild Manihot species have been described to date; the description of 5 other species is underway. Potential contributions of these species are as sources of low cyanide content, high starch content, resistance to several diseases and pests, and adaptability and tolerance to abiotic stresses (dry saline soils, lateritic acid soils with Al toxicity and low P content, cool temp.). Wild species conserved at genetic banks represent less than 2 percent of the collections; efforts, however, have been made and active collections are kept at CIAT, the Centro Nacional de Recursos Geneticos (Brazil), the Instituto Nacional de Investigaciones Forestales y Agropecuarias (Mexico), and the Ministerio de Agricultura/Instituto Agronomico Nacional (Peru) in the field, as seed, and in vitro. Thirty-two Manihot species and 26 genotypes of the putatively wild M. esculenta ssp. flabellifolia are conserved. Problems encountered in handling wild Manihot are poor seed germination, together with difficulties in stake propagation and in vitro conservation. Embryo culture has proved to have high potential in the conservation of wild cassava, especially for those species with few seeds or whose seeds lose their viability quickly. Cytogenetic studies indicate that genetic engineering techniques will hopefully be combined with traditional methods to make complex gene transfers from wild to cultivated species. The use of electrophoretic patterns of cassava protein to identify genotypes and species to be used for breeding is described. Isozyme markers can serve to identify interspecific hybrids and to detect occurrence of apomixis and genetic instability in cassava populations, as well as to eliminate duplicates in germplasm banks. Results of isozyme loci analyses for alpha and beta esterases are given. At CIAT, 35 wild Manihot species are conserved in vitro and as seed; in most cases, there are only one accession/species and only a few seeds or genotypes/accession.
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