Chromosomal Aberrations and Fertility Interrelationships in Prairie Bromus inermis Leyss. Populations

抄録

Thirty-five smooth bromegrass clones from naturalized populations were analyzed for structural chromosomal aberrations which included unoriented chromosomes at M-1, laggards at AT-1 and AT-2 and micronuclei at dyad and quartet stages. Other chromosomal aberrations encountered, were translocation configurations, inversion bridges and physiological disturbances of chromosomes. The primary objective of this investigation was to examine the nature of chromo-somal aberrations and to determine their influence on fertility levels in naturalized populations, and to compare with the results reported for artificially grown populations, of Bromus inermis. Results indicated that structural chromosomal aberrations such as unoriented chromosomes, laggards and micronuclei occur in naturalized populations at much lower frequencies than those reported for artificially grown populations. The frequency of micronuclei at the quartet stage could be used as an index of structural chromosomal aberrations during earlier stages. A significant negative correlation between quartet micronuclei frequency and stainable pollen indicated that fertility levels in naturalized polyploid populations of smooth bromegrass are appreciably lowered by structural chromosomal aberrations. Physiological disturbances included prophase pycnosis, stickiness at M-1, split metaphase plates, interchromosomal adnations in dyads, asynchronous divisions, heteropycnotic nodules on quartet nuclei and pentad or hexad formation at quartet stages. These chromosomal anomalies as well as fragments, translocation configurations and bridges were present at such low frequencies that the data was not amenable to a statistical treatment. The preponderance of bivalent formation at diakinesis supports the contention that the species has undergone considerable diploidization from the auto-allooctoploid stage of evolution.