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USDA-ARS, Forage and Range Res. Lab., Utah State Univ., Logan, UT 84322-6300
* Corresponding author (kevin{at}cc.usu.edu)
Leymus hybrid-1 wildrye germplasm (Reg. no. GP-82, PI 618816) was developed by the USDA-ARS, Forage and Range Research Laboratory in cooperation with the Utah Agricultural Experiment Station at Utah State University and released in January 2001. It was derived from a segmental alloautoploid population that originated from intercrossing three hybrids: (i) mammoth wildrye [Leymus racemosus (Lam.) Tzvelev (2n = 4x = 28)]/Altai wildrye [L. angustus (Trin.) Pilger (2n = 12x = 84)], (ii) Great Basin wildrye [L. cinereus (Scribner & Merr.) A. Löve (2n = 8x = 56)]/Altai wildrye, and (iii) a backcross hybrid, mammoth wildrye//Altai wildrye.
In 1982, seed of the above Leymus hybrid populations was acquired from Dr. Douglas Dewey at Logan, UT (Dewey, 1972, 1978). Population I was a cross between L. racemosus (PI313965)/L. angustus (PI314682) which produced a 70-chromosome hybrid that resulted from an unreduced L. racemosus egg (n = 28), fertilized by a reduced L. angustus gamete (n = 42). Population II was a 98-chromosome hybrid that originated from a cross that involved an unreduced L. cinereus (PI286809) gamete (n = 56) and reduced L. angustus (PI 314672 and 314682) pollen (n = 42). Population III was a backcross of L. racemosus//L. angustus. Chromosome numbers in the backcross population ranged from 76 to 78. In 1983, F2 seedlings from the three Leymus hybrids were established at the Evans farm near Logan, UT, in spaced-plant nurseries.
In 1984, cycle-1 open pollinated (OP) seed across hybrids from vegetatively superior plants were harvested from 20 F2 hybrids of L. racemosus/L. angustus, 17 F2 hybrids of L. cinereus/L. angustus, and 13 backcross (BC1) hybrids from L. racemosus//L. angustus. Cycle-1 seed was screened for seed yield, individual seed weight, and seedling emergence from deep (7.6 cm) planting in the greenhouse. In 1986, 50 half-sib families of the cycle-1 population were established at Logan, UT (mean annual precipitation 425 mm). Recurrent phenotypic selection for vegetative vigor and seed and seedling characteristics evaluated in cycle-1 was practiced for cycles 2 (1985) and 3 (1987).
A spaced-plant nursery of 700 cycle-3 plants was established at the Evans farm in 1988. In 1989, 15 additional paired crosses between superior F1 hybrids of L. angustus (PI314682) and L. cinereus (PI236820) and 17 cycle-3 plants selected for vegetative vigor, broadened the genetic base of the initial breeding population. Seed from the paired crosses and OP selected cycle-3 plants were harvested to constitute cycle-4. This breeding population was advanced through four more cycles of recurrent phenotypic selection conducted respectively at the Evans farm (1990–1992), Blue Creek, UT (1993-1994; mean annual precipitation 350 mm), Nephi, UT (1995-1996; mean annual precipitation 350 mm), and Evans farm (1997–1999). Plants with reduced plant vigor were removed prior to anthesis during cycles 5, 6, 7, and 8. In 1998 and 1999, equal amounts of seed from 10 selected half-sib families at Logan, UT, were combined to generate the Leymus hybrid-1 germplasm by means of a selection index that included forage yield, crude protein (CP) concentration, neutral detergent fiber (NDF) concentration, acid detergent fiber (ADF) concentration, total seed yield, and 100-seed weight.
Leymus hybrid-1 germplasm is highly cross-pollinated and behaves meiotically as a segmental autoallopolyploid that contains multiple copies of the Ns genome from the genus Psathyrostachys (wildryes) and the Xm genome whose diploid progenitor is not known. Leymus hybrid-1 germplasm flowers 2 to 3 wk later than Altai wildrye. Morphologically, Leymus hybrid-1 germplasm is 23% (P < 0.05) taller and has leaves 12% wider with improved vegetative vigor than currently available Altai wildrye cultivars Prairieland, Eejay, and Pearl. Spike characteristics and rhizome development are intermediate to the parental species.
In the Intermountain west, where annual precipitation ranges from 400 to 450 mm, dry matter (DM) production in the Leymus hybrid-1 germplasm exceeded the mean of the current Altai wildrye cultivars at mid-August by 36% and at late-November by 42% (Jensen et al., 2001). Under these environments, CP concentrations were lower (P < 0.05) in the Leymus hybrid-1 germplasm which averaged 61.5 and 28.6 g kg-1 compared to 80.5 and 34.1 g kg-1 in the check cultivars for summer and fall harvests, respectively (Jensen et al., 2002). Increased DM yields in the Leymus hybrid-1 germplasm more than compensated for the reduced CP levels. Fiber concentrations of ADF and NDF in the Leymus hybrid-1 germplasm were similar to the check cultivars of Altai wildrye. When evaluated on harsher sites where annual precipitation averaged 240 mm, DM yields, CP, and NDF were similar (P > 0.05) to the check cultivar Prairieland. Because of its increased DM yield in the fall, Leymus hybrid-1 germplasm should be utilized as a standing forage during the winter.
Seed yield, individual seed weight, and rate of seedling emergence from a 7.6-cm planting depth of Leymus hybrid-1 germplasm were lower (P < 0.05) than the mean of the check cultivars. Improving seed quality continues to be an emphasis of the breeding program. However, until it is improved, the seeding rates of Leymus hybrid-1 germplasm should be increased to 10 kg ha-1 in areas of adaptation. After emergence, seedlings are vigorous and persistent under semiarid conditions.
Seed stocks of Leymus hybrid germplasm are maintained by the USDA-ARS, Forage and Range Research Laboratory, Utah State University, Logan, UT 84322-6300 and are available in 20-g quantities upon written request. It is requested that appropriate recognition be made if this germplasm contributes to the development of a new breeding population or cultivar.
NOTES
D.R. Dewey (deceased). Utah Agric. Exp. Stn. Journal Article No. 7378. Registration by CSSA.
Accepted for publication September 30, 2001.
REFERENCES
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