Reduced quadrivalent frequency in C₁ colchiploids of Tithonia

Tithonia speciosa (Mexican sunflower) is a diploid with 2n=34. Morphological comparison of the diploid and C₁ generation tetraploid showed that the latter had bigger, long lasting capitula with increased number and size of ray florets. Auto tetraploids (2n=4x=68) in C₀ and C₁ 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 C₀ plants showed 60.8% pollen fertility and 30.4% seed set. Reduced quadrivalent frequency, increased bivalent fonnation and improved pollen (85.0%) and seed (67.0%) fertility as observed in C₁ plants may be due to lower chiasma frequency in the diploid and some preferential pairing in this outcrossing cultivar.