Cytogenetics and evolution of cassava (Manihot esculenta Crantz)

Abstract

All Manihot species so far examined, including cassava (Manihot esculenta), have 2n = 36. Interspecific hybrids between cassava and its wild relatives show fair regular meiosis, and backcrossed generations exhibit high fertility. Electrophoresis shows affinity between species of different sections, as well as between some of them and cassava itself. Polyploidy has apparently contributed to the rapid speciation of this genus, while apomixis has offered a means of perpetuating new hybrid types adapted to different environments. It is assumed that cassava originated by hybridization between two wild Manihot species followed by vegetative reproduction of the hybrid.

Case of escape in cassava, Manihot esculenta Crantz

“…M. flabellifolia represents another case for an escape that developed through hybridization of cassava with a wild species, followed by backcrossing with the cassava cultigen itself. Recent molecular evidence by Bredeson et al (2016) reveal that this form is the same as M. esculenta, confirming the assertion that cassava and M. flabellifolia are indeed the same species (Nassar, 2000;Nassar et al, 2008;Nassar and Ortiz, 2009).…”

“…Additionally, hybrids obtained from M. zehntneri and cassava were highly fertile with extremely regular bivalent pairing (18). This indicates that the plant form recognized as M. zehntneri by Ule is no more than an escape (Nassar, 1980(Nassar, , 2000. M. flabellifolia represents another case for an escape that developed through hybridization of cassava with a wild species, followed by backcrossing with the cassava cultigen itself.…”

Wild Manihot species: botanical aspects, geographic distribution and economic value

“…The Coastal Peruvian and lowland Neotropical cassava types differ, and appear to be separated by several millennia, which suggests that the crop may have been domesticated more than once. Nassar (1978aNassar ( , 2000aNassar ( ,c, 2003a emphasized the idea Nagib M.A. Nassar et al that M. esculenta species does not grow wild elsewhere.…”

Inducing autotetraploids in cassava using oryzalin and colchicine and their in vitro morphophysiological effects

“…Furthermore, polyploidization has been used to propagate the sterile cassava hybrid (Nassar, 2000) and to increase the rate of apomixis (Nassar, 2006), thereby enabling asexual reproduction of the mother plant. Conventional plant breeding has important obstacles to overcome; such as the time it takes to generate new cassava varieties (Oliveira et al, 2012) and the inherent difficulty of propagating certain cassava genotypes that do not produce flowers.…”