ISSN:
1439-0523
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Notes:
Microsporogenesis and megasporogenesis were cytogenetically and histologically analysed in three cassava clones:‘Rayong 1′,‘Rayong 60′,‘M. mga’ and two hybrid lines,‘OMR 3641-1’ and ‘OMR 3641-1’ to elucidate the evolution of sexual polyploids in cassava. At telophase II, formation of 17-21 micronuclei per pollen cell plate was observed in 16 out of 351 cell plates in ‘M. mga’. Micronuclei were observed at low (0.3-2.3%) frequencies, at the sporad stage in all clones. Monads, dyads, triads and tetrads, which are established sources of high ploidy levels were observed at low (2.6%) and high (22.2%) frequencies. Megasporogenesis in ‘Rayong 1’ and ‘Rayong 60’ showed a lack of second meiotic divisions after a successful first division that resulted in partly unreduced embryo sacs with 2n eggs, suggesting another unrecognized and, as yet, unreported source of sexual polyploid formation in cassava. Meiotic abnormalities during microsporogenesis and megasporogenesis are implicated as being responsible for the formation of mixoploids (triploids and tetraploids) in cassava breeding programmes. A cytogenetic mechanism resulting in bilateral sexual polyploids through different gametic fertilization pathways in cassava is suggested and its role in breeding is briefly discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1046/j.1439-0523.2002.00694.x
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