Chiasma frequency, distribution and terminalization in hexaploid oats (Avena sativa L.)

Chiasma counting has been regarded as the most straightforward method of scoring the total number of crossing-over events in the genome. In organisms in which genetic analysis is difficult or impossible to perform, it is a good estimator of the level of genetic recombination. In this paper we evaluated the chiasma frequency and distribution at diakinesis of twelve Brazilian oat varieties (Avena sativa), a hexaploid species with cytologically well-defined meiotic chromosomes. There was a high homogeneity of chiasma formation among varieties. The chiasma frequency per microsporocyte ranged from 41.66 to 42.00 among varieties. The frequency of interstitial and terminal chiasmata was more variable. The bivalents may present one, two or three chiasmata, but those with two terminal chiasmata were more frequent. The frequency of univalents was very low at diakinesis but high in metaphase I, suggesting precocious chiasma terminalization. The implications of these findings for oat breeding are discussed.