Genetically controlled desynapsis in diploid Critesion violaceum and its hybrids with autotetraploid Psathyrostachys juncea

Segregation for chiasma frequency was observed in the progeny of a diploid (2n = 14) Critesion violaceum strain following self-pollination. One S1 plant had normal metaphase pairing with an average of 0.43I + 6.78II, giving a high chiasma frequency, 12.03 per cell. The other S1 plant averaged 7.89I + 3.08II and a low chiasma frequency, 3.47 per cell. Examination of pollen mother cells at early prophases revealed that chromosome pairing was not totally prevented. It was concluded that desynapsis was responsible for the meiotic irregularities observed in the variant progeny. The same phenomena were observed in F1 hybrids of the cross between diploid C. violaceum and an induced autotetraploid (2n = 28), Psathyrostachys juncea. The normal F1 hybrid had a chiasma frequency of 12.81, but the desynaptic hybrid had a chiasma frequency of 6.94. A dosage effect of the desynaptic gene, which was probably recessive, was suggested. The implications and significance of this discovery are discussed.Key words: asynapsis, chiasma, meiosis, intergeneric hybrid.