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a Dep. of Plant Sciences
b Dep. of Animal Sciences; Univ. of Wyoming, Laramie, WY 82071
c School of Plant Biology, Univ. of Western Australia, Crawley, WA. 6009, Australia
* Corresponding author (jkrall{at}uwyo.edu).
‘Laramie’ (Reg. No. CV-274, PI 642951) is an annual medicago [M. rigidula (L.) All.] Tifton burclover cultivar developed and released in 2007 by the Wyoming Agricultural Experiment Station. Laramie is accession SA 10343 from the Annual Medicago Genetic Resource Center, Adelaide, SA. Laramie is released as a potential winter annual, self regenerating, ‘ley’ pasture species for the Central High Plains. Laramie was evaluated in Wyoming under the designate WY-SA 10343. This line was chosen for release for several key characteristics including winter hardiness (in southeastern Wyoming), production of abundant high quality spring forage, effective N-fixing relationship with alfalfa (M. sativa L.) rhizobium, effective regeneration from the soil seed bank, and acceptable forage for mid-summer grazing by dry ewes (Ovis aries).
Experimental lines and commercial medicago cultivars were established in the fall of 1994 in Laramie, Wyoming. On April 1, 1995 survival by species was as follows: M. polymorpha L. (0–3%), M. truncatula Gaertn. (3–5%), M. rigidula (55%), and (80%) for M. sativa. Plants of M. rigidula flowered beginning April 28 and produced mature seedpods by July 6 (Krall et al., 1996). To further assess for winter hardiness, 66 potentially winter hardy experimental lines from geographical origins in cold climates, representing eleven annual Medicago species were identified and tested along with seven commercial Australian annual Medicago cultivars in trials seeded in August 1995 at three locations in southeastern Wyoming. Medicago rigidula and rigiduloides E. Small. proved to be the most winter hardy species with 79% and 56% of lines, respectively, surviving at one or more locations in May 1996. Limited survival of M. orbicularis (L.) Bartal. (20%) and M. truncatula (13%) was observed. No experimental lines or cultivars of Medicago species: aculeate Willd., arabica (L.) Hudson., disciformis DC., littoralis Rhode ex Loisel., polymorpha, rugosa Desr., scutellata (L.) Mill., and tornata (L.) Mill. survived at any location. Laramie survived at all locations. From 1996 to 2005 (ten environments) Laramie has demonstrated acceptable levels of winter hardiness, with the exception of 2000–2001. This was one of the driest periods on record and winter desiccation is likely to have resulted in plant mortality.
Laramie was first evaluated for forage production in 1997 and 1998 (five environments) (Walsh et al., 2001). It was compared to 15 commercial cultivars and a M. rigiduloides accession (SA 3601). Laramie produced the highest mean dry matter (DM) forage yield (7.1 Mg ha–1), followed by M. truncatula cv. Paraggio (4.0 Mg ha–1), and SA 3601 (3.8 Mg ha–1). Laramie also had an acceptable level of seed production, yielding 5940 seed m–1, sufficient to establish a self-regenerating seedbank. Laramie was also chosen over M. rigiduloides (SA3601) because glasshouse experiments in 1993 revealed that it functioned with inoculant group AL while SA3601 would not function with this alfalfa inoculant group. Laramie, sown in August of 2002 and 2003, was evaluated for forage yield and nutritive value for livestock at 14-d intervals between mid-April to mid-June. Potential for regrowth was also assessed as well as natural reseeding. At the bud stage, approximately 15 April, there was a mean of 0.9 Mg ha–1 of DM forage, 14 d (flower stage) later forage production reached 1.7 Mg ha–1 of DM, by mid-May (full flower stage) DM forage production reached 3.8 Mg ha–1. In only one instance (mid-June, 2003), was acid-detergent fiber > 350 g kg–1. Only at the last sampling date for each year, when plants had passed to seedpod stage, did neutral-detergent fiber and crude protein (CP) values fall below 400 and 190 g kg–1, respectively. Although in-vitro dry matter digestibility was significantly (P < 0.05) lower in 2004, values remained above 650 g kg–1 with the exception of the last sampling time. Relative feed value remained >151 except for the final sampling and last two samplings in 2003 and 2004, respectively. Overall, >23% of the CP fraction is potentially leaving the rumen indicating low bloat potential. Stem length (SL) to free standing height (FSH) ratios were similar both years. They were 1:0.61 and 1:0.57 for 2003 and 2004, respectively. These ratios indicate a prostrate growth habit; however, FSH did reach a 2-yr mean maximum of 34 cm. This occurred at the end of May and indicates that cutting for hay or haylage is possible.
Post harvest regrowth of Laramie occurred up to and including the full flower stage (mid-May). The amount was measured 30 d after the mid-May harvest in 2003 and at the end of this period regrowth of 5.2 Mg ha–1 DM forage had occurred.
In 2004, when Laramie had reached the later stages of seedpod development, mature dry ewes were allowed to graze the standing crop for 28 d. At the outset of grazing mean body weight of the mature dry ewes was 78.9 ± 12.1 kg. After the mid-summer, 28-d grazing period mean ewe weight was 81.3 ± 11.6 kg. No ill effects were observed during the grazing period.
Autumn regeneration from the soil seed bank is critical for any ley Medicago forage species. A 5-yr soil seed bank experiment revealed that the seed softening pattern of Laramie fits within the desired seasonal softening level of 10 to 20% yr–1. This has been verified with 2 yr of field regeneration experiments. Six Australian cultivars regenerated from the soil seed bank at a mean rate of 31 and 3 plants m–2, one and two years after initial seeding, respectively. Regeneration was at least eight times higher for Laramie one and two years after initial seeding. Further examination of natural reseeding occurred in 2003–2004. Levels of percent ground cover one and two years following drill sown medic were significantly higher (P < 0.05) and equal to (P > 0.05) a drilled sowing, respectively.
Laramie is indeterminate, with long (53 cm, at pod stage) relaxed stems (<7 primary branches plant–1), and yellow flowers (three node–1). It has kidney-shaped seed with yellow cotyledons and seed coat color. The seed is born in a multiple coiled pod with spines of 1 to 2 mm in length. Mean 100 dry pod and seed weight is 9.0 and 0.41 g, respectively. Laramie, tested as SA 10343, was collected in Russia (E 46° 44'; N 44° 44') at 10 m elevation in a 700 mm annual precipitation zone in 1974. To the best of our knowledge SA 10343 is not grown commercially anywhere in the world.
Breeder seed of Laramie will be maintained by the Wyoming Agricultural Experiment Station. Currently the seed production and marketing of Laramie is retained by the University of Wyoming. Production of Laramie will only be through the Certified seed class. Laramie has been approved for trademark protection. A small quantity of seeds will be available for research purposes under a memorandum of understanding by contacting the corresponding author for six years from the date of publication. Seeds of this release are deposited in the National Plant Germplasm System where it will be available after three years for research purposes, including development and commercialization of new cultivars. It is requested that appropriate recognition be made if this germplasm contributes to the development of new germplasm or cultivars.
Acknowledgments
Laramie was developed with partial financial support from the USDA-WSARE program. Contribution no. JA 1791 from the College of Agriculture, University of Wyoming.
Footnotes
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References
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