Observações citológicas em Coffea. XIX - Microsporogênese em Coffea dewevrei

Abstract

Coffea Dewevrei De Wild, et Th. Dur. is a diploid species with 2n = 22 chromosomes. Details on the microsporogenesis are presented in this paper. From pachynema to diakynesis the 11 bivalents were well differentiated into achromatic and chromatic regions : the centromere was in all chromosomes surrounded by deeply chromatic zones. Only one pair of chromosomes was found to be attached to the nucleolus; it has a submedian centromere, the organizing region seeming to be located in the short arm. Chiasmata were seen in diakynesis and metaphase I; in this later stage they were studied in detail and the chromosomes were classified as follows : a) 1 longer pair with 3 chiasmata; b) 2.7 pairs (average) with 2 chiasmata ; c) 7.3 pairs (average) with 1 chiasma. The 2-chiasmata chromosomes were of two kinds : "symmetric" and "assymmetric", depending on the position of their chiasmata in relation to the centromere. The anaphase is normal, pollen grains having 11 chromosomes. Very seldon are pollen grains formed with 10 or 12 chromosomes. First mitosis in the microspores occurs before pollen shedding. It was concluded that microsporogenesis in the coffee plants studied is normal.