Cytological Studies in the Tribe Paniceae, Gramineae
1970 年 35 巻 1 号 p. 111-131
詳細
1970 年 35 巻 1 号 p. 111-131
Chromosome numbers were determined during microsporogenesis in strains belonging to 21 species and 8 genera of Paniceae. These include 4 new reports. Intraspecific chromosome races were found in Brachiaria brizantha, Cenchrus ciliaris, Digitaria adescendens, D. eriantha, Eriochloa nubica, Panicum maximum, Paspalum, orbiculare, P. plicatulum, Pennisetum pedicellatum, Urochloa mosambicensis and U. panicoides.
Meiosis was studied in all species. Chromosome pairing was regular in diploids but irregular in polyploids and aneuploids. It is suggested that polyploidy and meiotic irregularities are mechanisms which favor apomictic mode of reproduction in the members of Paniceae studied herein. The frequencies of quadrivalents observed in strains of Cenchrus ciliaris, Paspalum plicatulum and Paspalum simplex seem to be high enough to suggest their autoploid origin. In the rest of the species with low quadrivalent frequency, the factors favoring the accumulation of chromosome structural changes seem to be in operation.
Of special interest was a plant of Digitaria eriantha, which exhibited the phenomenon of breakdown of meiosis. The pollen mother cells at early prophase were without well differentiated cell walls, due to which several nuclei formed cenocytes. A few cells showed fragmentation of chromosomes. The metaphase stage was never reached. The fragmented chromosomes formed restitution nuclei. A few cells formed multiple spindles. The pollen fertility was very low.
The significance of the cytological findings was discussed.
