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Summary Partial or complete stickiness of chromosomes and disorientation of spindle were the major anomalies observed in meiocytes of Trigonella plants raised from seeds treated with different concentration of sodium azide for three durations. Other aberrations were unequal separation, non synchronous division, bridge, laggard, stray etc. The pollen fertility and yield showed an increase over control despite the high frequency of stickiness and spindle disorientation. Yield was positively correlated with stickiness, indicating a balancing/regulatory effect of stickiness at the time of gamete formation. Meiosis, an event of high evolutionary stability, plays a dual role as it halves the chromosome number in order to maintain ploidy level after fertilization and also ensures viability of gametes. It is a major event in the life cycle of any individual and a normal and harmonious completion of the cytological action is controlled by large number of genes, which act from pre-meiotic to post-meiotic stage. Mutation in these genes causes abnormalities that may or may not impair pollen fertility. Key wordsCytological studies constitute an important component in a breeding program involving the development of new original forms with the aid of experimental mutagenesis. The normal and harmonious course of meiosis ensures gamete viability, which if altered has a significant affect on the yield. The objective of this work was to study the meiotic behavior in pollen mother cells of sodium azide treated Trigonella foenum-graecum plants. The different concentrations of sodium azide caused meiotic abnormalities in high numbers, but surprisingly did not affect the pollen fertility and yield. The yield was significantly increased at some doses, contrary to the belief that aberration leads to abnormal gametes and hence low yield. Sodium azide has been reported to induce large variability for several characters viz. number of capsules per plant, number of seeds per capsule, size of the seeds and weight of 100 seeds in Capsicum annuum and mutants also exhibited high germination percentage and vigour over parental variety (Umalkar et al. 1981). The suitability of sodium azide, as a mutagen for T. foenum-graecum was investigated by assessing the type of cytological anomalies and correlating it with the seed yield per plant. Materials and methodsDuring our investigation, uniform sized seeds were treated with 0.10%, 0.15%, 0.20% and 0.25% freshly prepared sodium azide solution (pHϭ4), each for different durations (2 h, 4 h and 6 h) and the treated seeds after proper washing were sown along with control in pots. For meiotic studies, flower buds were taken from plants of each treatment. Appropriate sized flower buds were fixed in 1 : 3 iron saturated acetic acid and absolute alcohol for 24 h and there after transferred to 70% alcohol. Slides were prepared by squashing the anthers in Acetocarmine stain, gently heated to

Summary Mutagen-induced polyploidy can be considered to be a system of increasing genotypic plasticity so that aberrations at the genic and chromosomal level are easily tolerated by the plants. A tetraploid and a mixoploid mutant was induced in Trigonella foenum-graecum by sodium azide. Healthy seeds of Trigonella were treated with different doses of sodium azide. In M 2 screening, we found variants at 0.15% treatment for 4 h and at 0.25% treatment for 2 h and they were studied for morphological characters, meiotic behaviour, pollen sterility and stomata frequency. They were confirmed as tetraploid and mixoploid respectively and their surviving M 3 progeny was further studied on the same line. Meiotic studies showed different types of abnormalities for both. In mixoploid, the RAR increased from M 2 to M 3 but in tetraploid plant it decreased in M 3 generation. The number of chiasma per chromosome was reduced in M 3 generation for both the mutants. A comparison of the different anomalies in 2 generations of the tetraploid and mixoploid helps us to understand the reason for very high pollen sterility and negligible seed set in the tetraploid. Stickiness was increased in both, but the relative increase was less in tetraploid. Stickiness has been considered as a natural method of ameliorating stress and hence may be responsible for better performance of mixoploid. Laggards and spindle disorientation was significantly higher in the tetraploid as compared to the mixoploid.

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