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Biomass production represents a fundamental biological process of both ecological and agricultural significance. The genetic basis of biomass production is unknown but asssumed to be complex. We developed a full sib, [F.sub.1] mapping population of autotetraploid Medicago sativa (alfalfa) derived from an intersubspecific cross that was known to produce heterosis for biomass production. We evaluated the population for biomass production over several years at three locations (Ames, IA, Nashua, IA, and Ithaca, NY) and concurrently developed a genetic linkage map using restriction fragment length polymorphism (RFLP) and simple sequence repeat (SSR) molecular markers. Transgressive segregants, many of which exhibited high levels of heterosis, were identified in each environment. Despite the complexities of mapping within autotetraploid populations, single-marker analysis of vailance identified 41 marker alleles, many on linkage groups 5 and 7, associated with biomass production in at least one of the sampling periods. Seven alleles were associated with biomass production in more than one of the sampling periods. Favorable alleles were contributed by both parents, one of which is from the M. sativa subsp. falcata germplasm. Thus, increased biomass production alleles can be gleaned from unadapted germplasm. Further, the positive quantitative trait locus (QTL) alleles from the parents are partially complementary, suggesting these loci may play a role in biomass production heterosis.

Hybrids between Medicago sativa subsp, falcata and M. sativa subsp, sativa can result in high levels of heterosis for alfalfa forage production. However, commercially viable alfalfa cultivars also must have acceptable performance for other agronomic traits, including regrowth following harvest and appropriate autumn dormancy. In this study, we characterized an [F.sub.1] population derived from the cross of the two subspecies for the genetics of forage production, forage height, and forage regrowth at three harvests in two Iowa locations for 1 yr. Quantitative trait loci (QTLs) controlling these traits were mapped on a genetic linkage map developed from this population. Broad-sense beritabilities and genetic correlations among the traits were high. Marker alleles associated with QTLs for these traits were contributed by each parental genome, suggesting that both subspecies of cultivated alfalfa may contribute to the improvement of these traits. Multiple regression models accounted for between 11 and 44% of the trait variation. The most marker-trait associations were detected during the first harvest. Marker effects were generally similar across harvests. Markers associated with autumn regrowth tended to be different from those associated with regrowth earlier in the season, suggestive of the identification of autumn dormancy effects. The winter hardiness gene MsaciB is a candidate locus for yield and cegrowth, being associated with yield across three harvests and with autumn regrowth. A subset of alleles was associated with more than one of the traits. Major alleles for the three traits appear to reside primarily on linkage groups (LGs) 3, 4, 5, and 7.

A cytogenetic investigation was conducted on four historically putatively distinct nondormant alfalfa germplasm sources, African, Chilean, Peruvian, and Indian tetraploid alfalfa [Medicago sativa ssp. sativa (L.) L. & L.; 2n = 4x = 32]. C-banding, image analysis, and cluster analysis was used to test the hypothesis that chromosome structure differed among the four nondormant alfalfa populations. Cytogenetic analyses revealed polymorphisms for heterochromatic DNA in the number and location of constitutive heterochromatic DNA both within and among genotypes. However, this variability did not prevent recognition of homologous chromosomes. Karyotypes of Peruvian and Indian populations were developed. The reference African population was used to compare the karyotypes of Peruvian and Indian populations as well as the previously published Chilean population. In general, the number of heterochromatic DNA bands was similar for the African, Chilean, and Peruvian populations; however, the Indian population had significantly fewer heterochromatic bands than the other three. Cluster analysis based on all eight chromosomes yielded no clear separation of the nondormant alfalfa populations possibly because of the lack of chromosomal rearrangements, similar genetic backgrounds of the initial introductions, intercrossing of the different sources, genetic drift during maintenance, and/or common genetic backgrounds of the original parental germplasm sources., ALFALFA, the most important forage crop grown in the USA, is primarily harvested as hay for animal consumption but is also an important component of pastures. Nondormant alfalfa is particularly [...]

A cytogenetic investigation was conducted on the tetraploid alfalfa [Medicago satira subsp. sativa (L.) L. & L.] Chilean germplasm source PI 536534 using the combined techniques of C-banding and image analysis. Cluster and multiple correspondence analyses were utilized to compare the C-banding patterns of the Chilean germplasm source and the previously published African germplasm source. Cytogenetic analyses revealed polymorphisms for heterochromatic DNA in the 19 plants observed in detail. Abundant variability in the number, intensity, and location of constitutive heterochromatic DNA was noted; however, this variability was not sufficient to preclude recognition of homologous chromosomes. Five out of the 50 plants studied were aneuploids (2n = 4x + 1 = 33 or 2n = 4x - 1 = 31) because of the presence or absence of a chromosome with a satellite. The Chilean karyotype resembled the reference tetraploid African alfalfa karyotype; however, a reduction in the total amount of heterochromatic DNA was observed. Cluster analysis and multiple correspondence analysis based on all eight alfalfa genome chromosomes yielded no clear separation of Chilean and African germplasms. However, the analysis of C-banding patterns of Homolog 1 of Chromosome 8 in Chilean and African germplasms was effective in separating the two germplasm sources with the exception of two individuals from each germplasm source which clustered together., ALFALFA IS THE MOST important forage legume crop grown in North America and the third most widely grown crop in the USA (Barnes et al., 1988). Alfalfa is primarily harvested [...]

A reference karyotype of tetraploid alfalfa (Medicago sativa subsp. sativa, 2n = 4x = 32) African Population germplasm source (PI 536539) was constructed using the combined techniques of C-banding and image analysis. The image analysis system is a method of obtaining enhanced images of chromosomes in which morphological data can be obtained for the development of karyotypes. In addition, C-banding is a diagnostic tool for distinguishing the homologous chromosomes of alfalfa. Chromosome analysis of tetraploid alfalfa revealed that alfalfa has four similar series of chromosomes based on their chromosome morphology and C-banding. The karyotype of African Population alfalfa germplasm consists of one set of chromosomes with satellites (SATs, Chromosome 8), four sets of submetacentric chromosomes (Chromosomes 1-4), and three sets of metacentric chromosomes (Chromosomes 5-7). All of the chromosomes have centromeric bands and a terminal band on the short arm, with the exception of the SAT. Interstitial bands were observed on the short arm of each of the chromosomes, with the exception of Chromosome 7. Chromosomes 1, 2, and 3 have interstitial bands on their long arms. There exists considerable variability in the number, intensity, and location of the constitutive heterochromatic DNA; however, this variability is not sufficient to preclude recognition of the homologous chromosomes. The chromosome banding pattern of the African Population germplasm resembles the distribution of heterochromatic DNA C-bands of diploid M. sativa subsp. caerulea (Less. ex Ledeb.) Schmalh. The African Population karyotype of alfalfa developed in this study is suggested as the reference for the development of additional chromosome maps of diverse alfalfa populations., ALFALFA, a tetraploid (2n = 4x = 32), is the most important perennial forage crop grown in North America. It is recognized as a widely adapted agronomic crop, an effective [...]

The United States National Plant Germplasm System contains 3159 accessions from 36 species of annual Medicago. Although there is increasing interest in the annual medics for use in sustainable agriculture, the U.S. collection is under utilized because of lack of agronomic information. Development of a core collection could facilitate easier access to the germplasm collection and enhance its use. The core collection should consist of a sample of accessions that represents the range of variability within the germplasm collection with minimum redundancies. To select a core collection of annual Medicago species, a subset of 1240 accessions was evaluated during the summer of 1990 for 16 agronomic and morphological traits. Accessions within species were grouped by cluster analysis utilizing an unweighted pair group method with arithmetic averages. Intraspecific phenotypic diversity determined the number of accessions for that species selected for the core collection. One accession per cluster was selected for each species for the core collection. Accessions were chosen within a species to represent the greatest diversity in geographical regions. The selected core collection of 211 accessions was reevaluated during the summer of 1991. The core collection was found to represent the variability of the germplasm collection and to remain stable between the two evaluation years. This study can be used as a model method for selecting a core collection for multispecies germplasm collections.