MEIOTIC IRREGULARITIES IN INTERGENERIC HYBRIDS Helianthus annuus L. x Tithonia rotundifolia (Mill.) S.F. Blake

Abstract

Cultivated sunflower, Helianthus annuus, and wild species, Tithoni rotundifolia, are members of the Asteraceae family and share a common chromosome number (2n = 2x = 34). In this research, meiotic chromosome pairing was analyzed in H. annuus x T. rotundifolia intergeneric hybrids obtained in previous research, where all plants were sterile. The squash technique with carmine staining was used for meiotic cell preparation. The meiocytes in diakinesis, metaphase I and anaphase I were analyzed under a compound microscope. Meiosis in F1 hybrids showed highly irregular pairing, with presence of univalent and multivalent configurations, fast chromosomes, lagged chromosomes and bridges in anaphase I, as well as unbalanced dyads at the end of anaphase I. The observed abnormal pairing indicates irregular chromosome segregation causing male and female sterility, as previously in the intergeneric hybrids. It is inferred that parental genomes (HA 89 strain of H. annuus and T. rotundifolia Ac. 26) are incompatible in meiosis, causing unbalanced segregation that precludes viable gamete formation and impairs sexual reproductive capacity of hybrid plants.