Meiotic Behavior and Fertility Interrelationship in Andropogon scoparius and A. gerardi

Microsporogenesis, and fertility as measured by pollen stainability, were studied in 27 little bluestem and 24 big bluestem clones from four native populations over a two year period. Diakinetic analyses in little bluestem revealed a diploid chromosome number of 40, a chiasma frequency of 1.88 per bivalent and a low incidence of univalent and multivalent formations. Big bluestem was characterized by a diploid chromosome number of 60, a chiasma frequency of 1.77 and occasional multivalent associations. The presence of multivalents in these species indicate that they are segmental alloploids with incomplete diploidization.Predominant chromosome aberrations of microsporogenesis in these species were due to homology differences. These were observed as unoriented univalents at metaphase, lagging chromosomes at anaphase I and II, and micronuclei at dyad and quartet stages. Correlation of frequency of these irregularities among meiotic stages indicate that quartet micronuclei may be used as an index of aberration levels arising from homology differences.Correlation coefficients between meiotic chromosome aberrations and pollen stainability were generally negative and non-significant. Apparently, these aberrations are not solely responsible for the sterility levels in these species.Other forms of chromosome aberrations encountered, but too infrequent to be treated statistically were, inversion bridges at anaphase I and II, translocation rings at metaphase I and forms of physiological chromosome anomalies.