Secondary chromosomal association in kidney bean (Phaseolus vulgaris L.)

The present study documents the mutagenic efficacy of gamma ray and sodium azide on the chromosomal association pattern of bivalents and meiotic behavior in Phaseolus vulgaris L. The seeds were irradiated with different doses of gamma rays viz.10 krad, 20 krad, and 30 krad from a 60Co source and thereafter, the seeds were treated with 0.3% of freshly prepared sodium azide solution for three hours, respectively. The results clearly show the formation of various types of secondary chromosomal association among bivalents. Secondary association is defined as the tendency of bivalents to lie in pairs having diffused connections. The phenomenon of secondary pairing manifested from metaphase I stage and persisted upto metaphase II stage. The bivalents lie side by side and end to end to form secondary pairing. A secondary association between bivalents is considered to be of great significance as it is being taken as an indicator of ploidy in plants. Apart from secondary chromosomal association, other meiotic abnormalities were also noticed. These include precocious movement of chromosomes at metaphase I/II (2.83%), stickiness at metaphase I/II (3.45%), stickiness at anaphase I/II (2.20%), bridge (1.25%), unorientation (0.94%), micronuclei (1.88%) etc. This phenomenon, along with other meiotic aberrations affects the pollen fertility considerably.