Cytogenetic characterization of induced autotetraploids in grass pea (Lathyrus sativus L.)

Induction of polyploidy was successfully achieved in grass pea (Lathyrus sativus L.) variety BioR-231 using 0.10% (eight hours three days), 0.20% (six hours two days and eight hours two days), 0.30% (eight hours one day) and 0.40% (six hours one day) colchicine solution by apical shoot tip treatment of young seedlings. Compared to diploid variety the tetraploid plants were morphologically distinguished by luxuriant vegetative growth showing broader and thicker leaflets and stipules, flattened stems, increased number of branches, enhanced length of tendril as well as peduncle, delayed flowering and reduced pollen fertility. Number of stomata decreased but its size increased significantly in tetraploids. Presence of 711 and 7-7 separation at meiosis-I were the usual feature in diploids (2n=2x=14) while occurrences of 28 chromosomes in different combinations of multivalents, bivalents and univalents at metaphase-I and unequal separation of chromosomes toward the spindle poles, bridge formation, laggard at anaphase-I distinguished tetraploid (2n=4x=28) from diploid plants, cytogenetically. All these meiotic irregularities through the formation of unbalanced gametes have been ascribed for pollen sterility and reduced seed yield in tetraploid plants. Nature of origin, morphology and formation of trivalent as well as quadrivalent indicated autopolyploid nature of present tetraploids in grass pea. Occurrence of majority pairing as bivalents has also been discussed.