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, F1 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 variance 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.

A lfalfa, a perennial forage crop, experiences seasonal changes in growth patterns and morphology in the temperate regions of the world. Fall dormancy, referring to the characteristic growth reduction and decumbent shoot orientation of certain genotypes in autumn, typically occurs in late summer and early autumn as temperature declines and photoperiod shortens (Castonguay et al., 2006;McKenzie et al., 1988). For practical purposes, the dormancy level of alfalfa cultivars is ABSTRACT Alfalfa (Medicago sativa L.) is a widely planted perennial forage crop. Fall dormancy is generally negatively correlated with winter injury in alfalfa. To understand the genetic basis of the two traits, we identified quantitative trait loci (QTL) controlling autumn growth and winter injury using a tetraploid alfalfa F 1 population. In total, 601 marker alleles were scored from 78 restriction fragment length polymorphism (rFLp), 123 simple-sequence repeat (SSr), and 48 single nucleotide polymorphism (SNp) markers. Linkage maps were constructed for each parent separately. Both maps contained eight linkage groups (LGs), with a length of 898 cM for WISFAL-6 and 845 cM for ABI408. Using interval mapping, we identified 15 QTL from an across-environment analysis and 71 QTL within individual environments for autumn plant height; winter injury; and autumn shoot, crown, and root biomass across four Iowa environments. of the 71 QTL, 42 were identified at 18 chromosomal locations that were identified in multiple environments for the same trait. possible pleiotropic QTL that contributed to dry weight of shoot, crown, and taproot were found, which partially explained the observed genetic correlations between those traits. However, few QTL were related to both autumn plant height and winter injury, supporting the observation of no genetic correlation between the two traits in this study. These results indicated that the two traits could be manipulated independently and, possibly, efficiently improved using marker-assisted selection. Because most QTL identified in this study were mapped to intervals of at least 10 cM, validation and localization in additional populations is needed to facilitate application of marker-assisted selection.

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 F1 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 heritabilities 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 regrowth, 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.

Orchardgrass, or cocksfoot [Dactylis glomerata (L.)], has been naturalized on nearly every continent and is a commonly used species for forage and hay production. All major cultivated varieties of orchardgrass are autotetraploid, and few tools or information are available for functional and comparative genetic analyses and improvement of the species. To improve the genetic resources for orchardgrass, we have developed an EST library and SSR markers from salt, drought, and cold stressed tissues. The ESTs were bi-directionally sequenced from clones and combined into 17,373 unigenes. Unigenes were annotated based on putative orthology to genes from rice, Triticeae grasses, other Poaceae, Arabidopsis, and the non-redundant database of the NCBI. Of 1,162 SSR markers developed, approximately 80% showed amplification products across a set of orchardgrass germplasm, and 40% across related Festuca and Lolium species. When orchardgrass subspecies were genotyped using 33 SSR markers their within-accession similarity values ranged from 0.44 to 0.71, with Mediterranean accessions having a higher similarity. The total number of genotyped bands was greater for tetraploid accessions compared to diploid accessions. Clustering analysis indicated grouping of Mediterranean subspecies and central Asian subspecies, while the D. glomerata ssp. aschersoniana was closest related to three cultivated varieties.