Cytogenetics of an induced trisomic in Lathyrus sativus L. (grass pea)

An induced trisomic plant was detected in the M-2 generation of gamma-ray irradiated Lathyrus sativus L. (grass pea). Initially it was suspected as a mutant showing distinctive characteristic with earliness in flowering. It was later characterized as a trisomic (2n+1=15) by the presence of an extra chromosome mostly as a univalent (7II+1) and (6II+3I) or in trivalent association (6II+1III) in male meiocytes, the PMCs in the diploid displayed 7 bivalents at diakinesis and metaphase-I. In contrast to normal separation (7-7) at anaphase-I in diploid, trisomic showed unequal separation (8-7) or presence of a laggard (7-1-7). Presumably it was a primary type of trisomic having 'linear' and 'frying pan' shaped trivalent in most of its meiocytes. Pollen fertility and seed setting in the trisomic was found to be reduced as compared to normal diploids but level of seed fertility in the aneuploid was appreciably high. Barring a few in the trisomic, performance of most of the yield parameters and other quantitative traits was lower than that in the diploids. The gene (s) present on the extra chromosome may be attributed for such variations and specific contrasting modifications might have occurred due to mutation induced by radiation. Characters might have been affected or influenced in one way or other resulting in or enhancement in performance of the trisomic. It is too early to predict on the inheritance pattern of the trisomic phenotypes appearing in the ratio 1:15 (approx.) in the selfed progeny.