Genetic studies of selenium tolerance, regeneration from cell culture, and inbreeding depression in Medicago spp

Selenium (Se) is a naturally occurring element in soils. It is an essential nutrient for animals, but elevated levels are potentially toxic to plants and animals. One objective of the first study was to evaluate genetic variation for tolerance to Se in callus, germinating seed and whole plants of alfalfa (Medicago sativa L.) to determine whether in vitro or germination evaluation of Se tolerance is a useful predictor of the whole plant response. Significant variation among alfalfa genotypes for Se tolerance was found, but neither callus nor germinant responses were correlated with whole plant Se tolerance. Therefore, neither trait would be useful for breeding Se tolerance. Overall, the selenate form of Se was more inhibitory to growth of whole plants and callus, whereas radicle growth was more inhibited by selenite. A second objective of this study was designed to identify and develop Se-tolerant alfalfa using cell selection in vitro. Five regenerable genotypes of diploid {dollar}rm(2n=2x=16){dollar} and tetraploid {dollar}rm(2n=4x=32){dollar} alfalfa were cultured in standard Schenk and Hildebrandt (SH) medium containing different levels of selenite, selenate and the combination of the two. More than 70 plants were regenerated from Se tolerant cell lines from one tetraploid genotype that survived on media containing highly toxic levels of Se. However, subsequent tests failed to identify stable Se tolerance in these regenerates.; Regeneration of whole plants from cell culture is a key element for most plant biotechnology. The objective of the second study was to develop diploid alfalfa populations with high regeneration potential. Nine accessions of M. sativa ssp. falcata and 24 accessions of M. sativa ssp. coerulea were screened for regeneration potential, and two falcata accessions and one coerulea accession with moderate regeneration ability were identified. Regeneration was improved within the falcata populations to 100% and 93%, respectively by three cycles of recurrent selection. Regeneration was not significantly improved in coerulea by two cycles of phenotypic recurrent selection.; Medicago ruthenica Ledeb. is a wild diploid {dollar}rm(2n=2x=16){dollar} alfalfa native to dry, cold, heavily-grazed regions of Inner Mongolia and northern China. This species may prove useful for range improvement in Western North America, but little is known of the breeding behavior of this species. The objective of the third study was to evaluate the effects of inbreeding on this species. Three generations of selfing in M. ruthenica were performed. Inbreeding depression in the S{dollar}sb3{dollar} generation was so severe that no S{dollar}sb3{dollar} plant produced viable self-seed and therefore precluded production of more highly inbred generations. Forage yield and fertility in the S{dollar}sb1{dollar} and S{dollar}sb2{dollar} generations were compared with the original populations in a greenhouse experiment. The S{dollar}sb2{dollar} generation produced less herbage and cross- and self-seed than both the S{dollar}sb0{dollar} and S{dollar}sb1{dollar} generations, although the S{dollar}sb1{dollar} outperformed the S{dollar}sb0{dollar} generation.