Enigmatic Phenomenon of Secondary Association among Bivalents in Guar (Cyamopsis tetragonoloba (L.) Taub.)

Abstract

Cytogenetical assessment of pollen mother cells of Guar (Cyamopsis tetragonoloba (L.) Taub.) in response to treatment of chemical mutagen was done. Ethyl Methane Sulphonate (EMS) revealed possession of an enigmatic behaviour among chromosomal bivalents i.e. formation of secondary association. Chromosomes exhibited a unique tendency of getting associated in close proximity and form discrete pairs. The phenomenon of secondary chromosomal association has been ascribed to the existence of similar cohesive homology or malfunctioning in chiasma formation among the associating bivalents. The association of bivalents was witnessed to be executed in either end to end fashion or sideways association. Various other chromosomal abnormalities were found, but secondary association was the preponderant abnormality which exhibited a continuous increase in its magnitude with increase in EMS concentration. Along with secondary associations, stickiness of chromosomes at anaphase was observed in considerable frequency. A significant influence of chromosomal association on the post meiotic product was also experienced, which in turn, led to influence the meiotic index. Abnormal sporads in the form of triads, dyads, monads and polyads, alongwith normal tetrad were seen. Pollen fertility percent was seen to decline from control to the highest concentration of EMS due to anomalies of preceding stages.