The frequency and types of chromosomal variability in regenerated Avena sativa L. plants were assessed by detailed meiotic analysis on 655 regenerated plants. Tissue cultures were initiated from immature embryos of the varieties Lodi and Tippecanoe and maintained by monthly subculturing. Plants were regenerated from 4-, 8-, 12-, 16- and 20- month-old cultures. Regenerated plants with cytogenetic alterations were common, although Lodi cultures produced a higher frequency of cytogenetically abnormal plants at each regeneration cycle than Tippecanoe cultures. After four months in culture, 49% of Lodi regenerated plants were cytogenetically abnormal, whereas only 12% of Tippecanoe regenerated plants were abnormal. The frequency of cytogenetically abnormal, regenerated plants increased with culture age. After 20 months in culture 88% of Lodi regenerated plants and 48% of Tippecanoe regenerated plants were cytogenetically abnormal. The most common cytogenetic alteration was chromosome breakage, followed by loss of a chromosome segment resulting in a heteromorphic pair at diakinesis. Of the regenerated plants classified as cytogenetically abnormal, 41% of Lodi plants and 66% of Tippecanoe plants had lost a portion of one or more chromosomes. Other alterations included trisomy, monosomy and interchanges. Chromosome instability associated with oat tissue cultures has several possible uses.

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Autumn dormancy in alfalfa (Medicago sativa) is associated with agronomically important traits including regrowth rate, maturity, and winter survival. Historical recurrent selection experiments have been able to manipulate the dormancy response. We hypothesized that artificial selection for dormancy phenotypes in these experiments had altered allele frequencies of dormancy-related genes. Here, we follow this hypothesis and analyze allele frequency changes using genome-wide polymorphisms in the pre-and post-selection populations from one historical selection experiment. We screened the nondormant cultivar CUF 101 and populations developed by three cycles of recurrent phenotypic selection for taller and shorter plants in autumn with markers derived from genotyping-by-sequencing (GBS). We validated the robustness of our GBS-derived allele frequency estimates using an empirical approach. Our results suggest that selection mapping is a powerful means of identifying genomic regions associated with traits, and that it can be exploited to provide regions on which to focus further mapping and cloning projects. KEYWORDS selection mapping alfalfa dormancy Alfalfa (Medicago sativa) is a highly nutritious forage used as hay, silage, and pasture for dairy and beef cattle. The major trait used to classify alfalfa germplasm is the expression of autumn dormancy (or "fall dormancy"), a plant's response to decreasing photoperiod and temperature (and possibly light quality) in autumn (Castonguay et al. 2006). The onset of dormancy in autumn occurs during a period of acclimation that eventually concludes with the expression of cold and desiccation tolerance (Thomashow 1999; McKenzie et al. 1988). Further, these changes in metabolism are associated with the slowing and eventual complete cessation of growth during the dormant period. Dormant germplasm exhibits reduced growth and an increased decumbent shoot orientation in autumn compared with non-dormant germplasm, which continues to grow upright. This process allows the dormant plants to survive stress until favorable conditions for growth return. Such seasonal rhythms of dormancy are observed in both woody and herbaceous perennial species (Thomashow 1999). Autumn dormancy in alfalfa is under complex quantitative genetic control. However, results from inheritance studies indicate that additive components of the genetic variance of the trait are generally of more importance than the nonadditive components (Daday and Greenham 1960; Castonguay et al. 2006). This suggests the potential for selection programs to effectively make gains for the trait in variable populations, as has indeed been successfully implemented (e.g., Cunningham et al. 1998). Across multiple populations, phenotypic selection for increased or decreased autumn plant height resulted in either more or less winter injury, respectively (Cunningham et al. 1998); conversely, selection for decreased winter injury resulted in a decrease in autumn plant height (Weishaar et al. 2005). The relationship between the traits, when ev...

Polymerase chain reaction was used, with single 10-mer primers of arbitrary sequence, to amplify random regions of genomic DNA from a diploid cultivated alfalfa backcross population. Segregation of the random amplified polymorphic DNA (RAPD) fragments was analysed to determine if RAPD markers are suitable for use as genetic markers. Of the 19 primers tested, 13 amplified a total of 37 polymorphic fragments, of which 28 (76%) segregated as dominant Mendelian traits. RAPD markers appear useful for the rapid development of genetic information in species like alfalfa where little information currently exists or is difficult to obtain.

The inheritance of 2n pollen formation was studied in two diploid clones of alfalfa, Medic-ago suriva L. The two clones consistently produced a high frequency of 2n pollen, and they also porduced good seed set when used as males in 4.r-2x crosses due to the functioning of 2 n ( 2 x ) pollen. For the inheritance study the two clones were crossed with diploid clones of cultivated alfalfa at the diploid level (CADL), and with several clones of diploid M. fulcura. In segregating families, plants that produced a high frequency of 2n pollen were identified by good seed set when used as males in 4.r-2.r crosses, andlor by bimodal pollen sizes. Plants that produced 4% or more 2n pollen generally produced greater than one seed per pollination in 4x -2x crosses, and these plants were considered 2n pollen producers. Analysis of self, F,, F, and backcross (BC) families indicated 2n pollen formation was controlled by a single recessive gene, designated rp (restitution pollen). An allelism test indicated 2n pollen formation was controlled by the same recessive gene in both clones. Although there was considerable variation in the frequency of 2n pollen in rplrp plants grown in different environments, all rplrp plants consistently produced a significant frequency of 2n pollen (greater than 4%). Simple genetic control of 2n pollen formation has important implications in the evolution of the genus Medicago. In addition, 2n pollen formation controlled by a single gene may have potential application in the breeding of highly heterozygous tetraploids and in the efficient transfer of germplasm across ploidy levels.On a etudie la transmission genetique de la capacite de formation de pollen 2n chez deux clones diploi'des de luzerne Mcdic.clgo sutiva L.. Les deux clones ont constamment fourni un haut taux de pollen 2n ainsi qu'une bonne production de semences lorsqu'utilises comme miles dans des croisements 4x-2x ceci etant attribuable a I'action du pollen 2n(2.r). Pour cette etude on a croise les deux clones avec des clones diploldes de luzerne cultivee au niveau diploide (CADL) et avec plusieurs clones du diploi'de M. fillc,clro. Lors de la separation des familles, les plants qui ont fourni un haut taux de pollen 2t1 ont ete identifies par une bonne production de semences lorsque utilises comme miles dans les croisements 4.r-2.r, ou encore par les dimensions bimodales du pollen. Les plants qui fournirent 4% ou plus de pollen 2n ont generalement fourni plus d'une graine par pollinisation dans les croisements 4 x -2 x , et ces plants ont ete retenus comme fournisseurs de pollen 2 n . L'analyse des familles des autopollinises, des F,, des F, et des retrocroisements (BC) a indique que la formation du pollen 2n etait imputable e un seul gene recessif, nomme rp (restitution pollen). Un test d'allelisme a revele que la formation de pollen 2n etait imputable au m6me gene recessif chez les deux clones. Quoiqu'on air note une variation importante du taux de formation de pollen 2n chez les plants rplrp cultives dans des environnements differents,...