Contrary to views that cassava (Manihot esculenta) is only known in cultivation an argument is made that wild accessions of the species grow over much of the American neotropics, in Brazil, Bolivia, Peru, Venezuela, Guyana, and Surinam . Three subspecies are recognized . M . esculenta subsp . esculenta is the domesticate and includes all cultivars known in cultivation . The wild M . esculenta subsp . peruviana occurs in eastern Peru and western Brazil . The wild M. esculenta subsp . flabellifolia shows a wider distribution and ranges from the central Brazilian state of Goias northward to Venezuelan Amazonia . The large area of distribution of the two wild subspecies makes it difficult to assign a place of initial domestication .
Despite the worldwide importance of cultivated cassava (M. esculenta Crantz) its origin and taxonomic relationships with other species in the genus have not been clearly established. We evaluated a representative sample of the crop's diversity and six wild taxa with AFLPs to estimate genetic relationships within the genus. Groupings of accessions of each species by data analysis corresponded largely with their previous taxonomic classifications. A mixed group, consisting of Manihot esculenta subsp. flabellifolia and M. esculenta subsp. peruviana, was most similar to cassava, while M. aesculifolia, M. brachyloba, and M. carthaginensis were more distant. Species-specific markers, which may be useful in germ-plasm classification or introgression studies, were suggested by the unique presence of AFLP products in samples of each of the three wild species. Heterogeneity of similarities among individuals of certain species suggested the existence of intraspecific gene pools, a hypothesis that was supported by morphological or ecogeographic evidence with varying degrees of success. Quantitative assessment of genetic diversity revealed greater homogeneity among cassava accessions than among its closest wild relatives. The demonstration of unique genetic diversity in the two M. esculenta subspecies and their genetic similarity to the crop supports the hypothesis that these materials may be the ancestors of cassava.
The Origins and Taxonomy of Cassava 3 4 A.C. Allem Basionym Novel status Category M. esculenta Crantz M. flabellifolia Pohl M. peruviana Mueller M. esculenta Crantz ssp. esculenta M. esculenta Crantz ssp. flabellifolia (Pohl) Cifferi M. esculenta Crantz ssp. peruviana (Mueller) Allem Cultivated stock Wild strain Wild strain From Allem (1994a). a Because cassava is known to include cultivated and wild forms, the species is no longer a cultigen but ranks as an indigen instead. The definitive infraspecific classification of the species is in preparation. There is a real possibility that two other species (e.g. Manihot leptophylla) join the extensive synonymy of the complex. In addition, a further wild variety with smooth fruits found in May 1994 and so far only known from the northern Brazilian Amazonian state of Tocantins awaits description. Table 1.1. The subspecies of cassava. a Species Range M. carthaginensis M. aesculifolia M. grahami M. flabellifolia M. saxicola a All countries bordering the
-The occurrence of polyembryony was investigated in 75 woody species of the Cerrado in central Brazil and the xerophilous Caatinga vegetation in northeastern Brazil. Fourteen species showed polyembryony, a type of anomalous angiospermous reproduction. Polyembryony is reported for the first time for nine genera, Astronium, Byrsonima, Cariniana, Copaifera, Hancornia, Magonia, Myracrodruon, Tabebuia, and Tapirira. The positive correlation found between polyembryony, sexual reproduction, and apomictic processes suggests that a number of angiospermous species may make regular use of multiple breeding systems.Keywords -angiosperms, agamospermy, apomixis, polyembryony, Brazilian neotropics RESUMO -A ocorrência de poliembrionia foi investigada em 75 espécies lenhosas do Cerrado do Brasil central e da Caatinga xerófila do nordeste brasileiro. Quatorze espécies apresentaram poliembrionia, uma modalidade de reprodução anômala em angiospermas. Poliembrionia é relatada pela primeira vez para nove gêneros, Astronium, Byrsonima, Cariniana, Copaifera, Hancornia, Magonia, Myracrodruon, Tabebuia e Tapirira. A correlação positiva encontrada entre poliembrionia, reprodução sexual e processos apomíticos sugere que parte das espécies de angiospermas faça uso regular de sistemas de cruzamento múltiplos.Palavras-chave -angiospermas, agamospermia, apomixia, poliembrionia, neotrópico brasileiro Recebido em 29/09/00. Aceito em 25/07/01.
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