Resumen

DE GUERRA, Nilda Alcorcés; LAREZ R, América  y  MAYZ F, Juliana. Additions to the cytogenetic knowledge of Tithonia diversifolia (Hemsl.) A. Gray (Asteraceae). Acta Bot. Venez. [online]. 2007, vol.30, n.2, pp.267-275. ISSN 0084-5906.

With the objective of corroborating the chromosomal number, the pollen size, type and viability, in a study of the meiosis of Tithonia diversifolia, meristematic root tips treated with colchicine (0,05%) and young inflorescence anthers, collected from different localities of Monagas State, Venezuela, were studied. A diploid chromosome number (2n = 34) was found,with 16 metacentric pairs and one submetacentric pair. Lagging chromosomes in me-taphase I and anaphase I, and asynchrony in metaphase II were observed. Spermatic nuclei could not be seen in 65% of pollen grains. Abnormalities which may be associated with the low pollen fertility (35%) were detected in this species. Pollen grains were of triporate type and had muricate sculpture, with an average size of 26.5 mm. The microsporogenesis was of the simultaneous type.

Palabras clave : Chromosomes; Cytogenetic; Meiosis; Microsporogenesis; Mitosis; Tithonia diversifolia.