Tithonia speciosa (Mexican sunflower) is a diploid with 2n=34. Morphological comparison
of the diploid and Cl generation tetraploid showed that the latter had bigger, long lasting
capitula with increased number and size of ray florets. Autotetraploids (2n=4x=68) in Co
and Cl generations showed mean chromosome association/pmc as 8.5 IV + 1.3 III + 14.3 II
+ 1.5 I and 3.6 IV + 1.7 III + 23.4 II + 1.7 I, respectively at MI. Anaphase 1 appeared nonnal
with 34:34 distribution. The Co plants showed 60.8% pollen fertility and 30.4% seed set.
Reduced quadrivalent frequency, increased bivalent fonnation and improved pollen
(85.00/.) and seed (67.0%) fertility as observed in Cl plants may be due to lower chiasma
frequency in the diploid and some preferential pairing in this outcrossing cultivar.
Keywords: Tithonia, quadrivalent, colchiploids, chiasma, preferential pairing.
Article DOI: NA
Print ISSN: 0019-5200
Online ISSN: 0975-6906
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