ABSTRACT

This study reveals different meiotic features from three zones of inflorescence of four parents and their F₁ and F₂ hybrids. Increase in chiasma frequency in zone II were found with the increase of both bivalent and quadrivalent. On the contrary, decrease of univalent and trivalent was observed in most of the parents and hybrids. Comparatively zone I showed lowest values for all these characters and zone II was found to show highest percentage of regular tetrads and fertile pollens followed by zone III. Regression analysis was found to be negative in percents and hybrids regarding the relationship of chiasma frequency and trivalent frequency for all the three zones. On the other hand, regression was found to be positive for all zones in parents and hybrids in terms of the relationship of chiasma frequency with bi and quadrivalent frequency. Different types of meiotic irregularities were also observed and more than 80% pollen grains were fertile for all the zones of parents and hybrids except the tip sterile line FM-147, where it was 60-70%. There was no evidence of any recessive gene, which may affect pairing in one of the population. The meiotic irregularity is lethal to semi lethal which limits the success of selection and a little diverging tendency in few the F₂ hybrids is not significant.

Key words: Meiosis, parents, hybrids, bread wheat

Introduction Triticum aestivum is an allohexaploid but behaves as a diploid during meiosis. The relationship between chromosome homology and chromosome pairing is the basis of genome analysis. However, chromosome pairing can be affected by asynaptic or desynaptic genes or by unusual external environment (Lin, 1982). These factors play role on chromosome pairing in hybrids of hexaploid wheat and affect the assessment of chromosome homology. Moreover, it may be said that chromosome pairing at first meiotic metaphase in hybrids of hexaploid wheat has been used to elucidate genomic relationship intra specifically. Nevertheless, genetic control of pairing can complicate comparisons in some polyploids such as hexaploid wheat, even in case of the hybrids of these wheat species. In such cases chromosome pairing in controlled by a diplodizing mechanism which consists of a number of major or monor genes, which acts in opposition to each other but sometimes eighter promote or suppress homoeologus chromosome pairing. In general meiosis in this crop species (hexapliod wheat) is found to show regular bivalent formation. But sometimes wheat line such as FM-147 (hybrid progeny of Falchelto and Mexicani varieties) shows undesirable meiotic behaviour like quadrivalent (ring/ chain) formation. This time shows apical sterility of the spike and when it is crossed into any normal varieties/lines the progenies are found clearly with apical sterility. The progenies also show quadrivant formation in addition with bivalent configuration. The present study deals meiotic abnormalities of three Bangladeshi varieties (registered) and their progenies when crossed with FM-147 with a view to visualize the unusual effect of meiotic behavior of tip sterile line on normal varieties of Bangladesh.