Gamma irradiation induced multiple chromosome interchanges in Hordeum vulgare L. (Poaceae): meiotic characterization and their implications on pollen fertility

Abstract

Barley (Hordeum vulgare L.) is an important cereal crop with 2n = 2x = 14 chromosomes. Gamma irradiation treatments to barley seeds successfully induced four multiple translocation heterozygotes (T-1, T-2 and T-3 from 25 kR, and T-4 from 20 kR) in M1 generation. In meiosis I, microsporocytes of T-1, T-2 and T-3 heterozygotes showed 2 rings/chains of four chromosomes, whereas T-4 displayed a ring/chain of six chromosomes. In this study, quadrivalents showed preponderance of ring configurations (ranged from 63.27 to 69.42%), while majority of hexavalents revealed chain configurations (63.41%). Due to meiotic instability, hexavalents sometimes gets dissociated into pentavalents, quadrivalents, trivalents along with univalents and bivalents. Assessment of orientation pattern of interchange complexes in the heterozygotes indicated alternate disjunction to be more frequent than adjacent type of disjunction. Presumably, involvement of more number of non-homologous chromosomes in translocation heterozygotes resulted in increased chromosome irregularities during meiotic segregation which ultimately led to much higher pollen sterility and concomitant decrease in growth and seed formation. In addition, pollen sterility (ranged from 47.97 to 58.09%) showed positive and significant correlation (r2 = 0.6222) with adjacent segregation of multiples (37.84–44.61%) in translocation heterozygotes.