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Embryology and cytogenetics of sexual tetraploid Eupatorium inulaefolium H.B.K.

James R. Coleman

Departamento de Botânica, Instituto de Biociências, Letras e Ciências Exatas, UNESP, 15055 São José do Rio Preto, SP, Brasil

ABSTRACT

Embryological studies show Eupatorium inulaefolium to regularly undergo reductive meiosis with tetrad formation during megasporogenesis, followed by monosporic embryo sac development of the polygonum type. The polar nuclei mostly fuse before anthesis, but endosperm formation is generaly initiated only after the embryo is already several-celled. Meiosis of microsporogenesis results in the regular formation of 20 bivalents; subsequent stages of microsporogenesis are normal, and stigmatic loads indicate the regular occurrence of pollination with viable, functional grains. Karyotypic studies revealed a complement of 40 chromosomes separable into 20 pairs, 15 with median and five with submedian centromeres, which have mean lengths ranging from 2.65 mm to 3.64 mm . The complement shows two SAT-chromosomes which are characterized by having the highest arm ratio. It is concluded that E. inulaefolium, as represented by the material studied, is of allotetraploid origin and is probably strictly sexual.

Keywords: Embryology; Cytogenetics; Sexual tetraploid; Eupatorium inulaefolium.

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