Cytogenetics of garden Gladiolus II. Variation in chromosome complement and meiotic system.

Abstract

Based on x=15, the species in the genus depict a range of ploidy from diploid (2n=30) to dodecaploid (2n=180), whereas all the garden coultivars studied are tetraploid (2n=60). The two diploid taxa G. tristis L. and Acidanthera bicolor Hochst. show regular meiosis with 15 bivalents and near normal pollen stainability. Among tetraploid (2n=60) taxa, G. italicus Mill. is characterised by regular occurrence of 30 bivalents leading to normal anaphase segregation and 91.6 per cent pollen stainability. The garden cultivars, however, show at metaphase I predominant bivalent formation with some quadrivalents, trivalents and univalents. While normal anaphase I segregation (30:30) was observed in most of the cells, unequal segregation also resulted due to trivalents and univalents. Pollen stainability ranges from 49.8 to 98.6 per cent. The pentaploid taxa comprising of six cultivated types of G. psittacinus hybr. also exhibited predominant bivalent formation along with pentavalents, quadrivalents, trivalents and univalents. Anaphase I is irregular due to unequal disjunction of trivalents and univalents. Pollen stainability ranges from 65.07 to 94.2 per cent. G. communis (2n=176) is characterized by trivalents, bivalents and univalents. Bivalent formation is unexpectedly high with a mean of 84.75 per cell and full complement of 88 bivalents was observed in 20 per cent of the cells studied. Pollen stainability is 87.16 per cent.A correlation of ploidy with general geographical distribution shows that the species native to Cape Winter-Rainfall region are diploid and those occurring in Summer-Rainfall region and Tropical Africa range from diploid to hexaploid; while Mediterranean, European and West Asian species are all polyploid, ranging from tetraploid to dodecaploid.