Cytogenetics of Manihot species and interspecific hybrids
1993
Bai, K.V. | Asiedu, R. | Dixon, A.G.O.
The genus Manihot comprises about 98 species, 22 of which are available in IITA's collection. These are being used to broaden the gene pool available to the cassava breeding unit. All the species, including cassava (M. esculenta Crantz), have a chromosome number of 2x = 36 and form 18 bivalents at probase-1 and metaphase-1 (M-1). Wide hybridization with cassava as well as between wild species using 12 of the available Manihot species was affected. The contrasting parental characters showed partial to total dominance in the F1 hybrids. Attempts were made to identify the chromosomes individually in the species using karyomorphological criteria. Most bivalents were identifiable from characteristics such as telechromomeres, distribution of heterochromatin, association with nucleolus etc. This was especially so with about 10 bivalents. Chromosomal similarities and differences based on their karyomorphology at pachytene stage in different Manihot species were established. Through chromosomal pairing in the F1 hybrids, the homoeologous partners were identified. A general decrease in the chiasma frequency at M-1 in the F1 was observed compared to parents. The presence of chromosomal structural differences was revealed by non-pairing of chromosomes, anaphase 1 bridges and fragments etc. Pollen fertility of the F1 hybrids varied considerably
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