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SELECTION FOR ENHANCED SEEDLING
ESTABLISHMENT IN COOL-SEASON
RANGE GRASSES
Douglas A. Johnson
KayH.Asay
ABSTRACT
Characterization of the Environment
Improved stand establishment should be a major objective of most range plant breeding programs. Various seed
and seedling characteristics have been evaluated for their
ability to predict field establishment in breeding lines of
crested wheatgrass (Agropyron cristatum [L.] Gaert. and
A desertorum [Fisch. ex Link] Schult) and Russian
wildrye (Psathyrostachys juncea [Fischer] Nevski). Seed
weight and ability to emerge from a deep planting depth
are the two characteristics that have been most closely associated with field establishment. Selection for these characteristics has been instrumental in the release of 'Nordan'
and 'Hycrest' crested wheatgrass and 'Swift,' 'Mankota,'
and 'Bozoisky-Select' Russian wildrye. Results from this
work indicate that significant improvement in stand establishment can be made in cool-season range grasses.
Many environmental factors affect the growth and production of cool-season range grasses on semiarid rangelands (fig. 1); however, drought is probably the most
prominent environmental stress on western U.S. rangelands (Johnson 1986b). Although drought can influence
plant growth and development at any phenological stage,
drought has particularly deleterious effects at the germination and seedling establishment phases. Drought can
interrupt the germination process, arrest seedling development, and cause seedling mortality.
Seedlings are particularly susceptible to drought because they have not accumulated carbohydrates necessary
to support maintenance respiration during the drought
period or developed extensive root systems for extracting
water and nutrients from deep soil depths. Consequently,
seedlings have few options available to withstand exposure to drought.
Seedlings of range plants typically are exposed to low
temperatures during establishment. Early spring and
late fall are periods when water availability is typically
most favorable for seed germination and seedling establishment on rangelands of the Intermountain region.
However, low and freezing temperatures are common during this period, making it necessary for seedlings to have
adaptations that allow them to grow and survive under
low temperatures.
INTRODUCTION
The objectives for seeding desirable cool-season range
grasses into semiarid rangelands include (Stoddart and
others 1975): revegetation of deteriorated rangelands and
abandoned croplands, vegetation replacement following
fire, expansion of the grazing season, improvement of the
quantity and quality of forage, and protection against erosion. Use of seeding mixtures that contain well-adapted
species with a high probability of successful establishment will optimize the returns from range seedings.
Johnson (1980, 1986a) and Johnson and others (1981)
discussed the five main points that must be addressed for
meaningful progress in any plant improvement program:
(1) characterization of the environment, (2) identification
of the selection criteria, (3) assemblage of a broad genetic
base, (4) development of reliable screening techniques,
and (5) incorporation of the screening techniques into the
breeding program. In this paper, we will discuss range
plant improvement in relation to these five points and
provide examples of how this process has been used to
develop improved cool-season range grasses for the Westem United States.
Temperature
Salinity
Aeration
_
Water
-----r"___;~ ___:./:.._~,_,-- Competition
----.1
Light
Winter
Damage
Germination
Seedling
emergence
Establishment
~/
Pathogens
Mycorrhizae
+---- Chemicals
1
t '-...____
Grazing
""
Soil
Impedance
Figure 1-Environmental factors that are
known to affect germination, emergence, and
establishment of range plants (from Johnson
1986b).
Paper presented at the Symposium on Ecology, Management and Restoration of Intermountain Annual Rangelands, Boise, ID, May ia-22, 1992.
Douglas A Johnson and Kay H. Asay are Plant Physiologist and
Research Geneticist, respectively, U.S. Department of Agriculture
Agricultural Research Service, Forage and Range Research Labo~tory,
Logan, UT 84322-6300.
337
Insects
Identification of Selection Criteria
techniques as an integral component of any plant improvement program. These techniques are used to evaluate the phenotypic expression of the desirable characteristic in the base breeding population, and then individuals
that best exhibit these traits are selected and used as
parents for the next generation (fig. 2). If the measured
characteristic is genetically heritable, progeny of these
selected parents will exhibit a higher mean expression for
the desirable characteristic than the base population. Additional selection cycles could lead to further advances in
the expression of the desirable characteristic.
A number of requirements must be met for a technique
to be used in a plant breeding program. Johnson (1980)
and Johnson and others (1981) indicated that plant screening techniques should (1) assess plant performance at the
critical development stage, (2) be completed in a relatively
short time, (3) use relatively small quantities of plant
material, and (4) be capable of screening large populations. Few techniques are able to meet these stringent
requirements.
The ability of seedlings to establish under rangeland
conditions is related to seed size in many range species
(Asay and Johnson 1980; Berdahl and Barker 1984; Hunt
and Miller 1965; Plummer 1943; Rogier 1954b). Generally, large-seeded strains within a species emerge sooner
from deeper planting depths and grow more rapidly than
do small-seeded strains. As a result, seed weight has
been suggested as a reliable characteristic for improving
seedling establishment. However, characteristics of long
coleoptile length (Berdahl and Barker 1984; Hunt and
Miller 1965) and emergence from a deep planting depth
The ability of seedlings to establish is critical for stand
success, and the advantages gained at the seedling stage
frequently are retained through the mature plant stage
(TeKrony and Egli 1991). Harper (1977) defined establishment as the time "when the seedlings have expanded
a photosynthetic surface and are theoretically capable of
pursuing an existence independent of their seed reserves."
Because of a generally low photosynthetic capacity and
very limited carbon and nutrient reserves, seedlings are
particularly susceptible to stresses such as drought, low
and high temperatures, and defoliation.
The term seedling vigor often is used to described the
general aggressiveness of seedlings to germinate, emerge,
and become established (Kneebone 1972; McKell1972).
The ability of seeds to rapidly germinate under cold conditions, initiate early root development, and quickly extend
their roots into the underlying soil layers enables seedlings to effectively compete with nondesirable range species such as cheatgrass (Bromus tectorum L.). In addition,
these characteristics assist seedlings to avoid the effects
of drought caused by evaporative water losses of the upper soil layers. Also, growth during the early, cool portion
of the growing season, when vapor pressure deficits between the atmosphere and leaf are at a minimum, increases the efficiency of water use. Growth during this
period allows a greater proportion of the water to be utilized for transpiration and subsequent growth than is lost
by evaporation from the soil. Consequently, the ability of
seedlings to rapidly establish under low temperatures and
withstand drought are key characteristics that should be
selected for and improved in a breeding program for coolseason range grasses. Johnson and Asay (1993) comprehensively reviewed the literature pertaining to selection
for improved drought response in cool-season grasses.
40
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~ 30
Assemblage of a Broad Genetic Base
\
~
l
Genetic advance in a plant improvement program critically depends on assembling a broad genetic base of germplasm from plant introductions, released cultivars, experimental strains, and old plantings. The greater the
diversity of the germplasm base, the greater likelihood
that the gene pool contains variation for the particular
characters that will be selected. Potential progress in a
breeding program is directly tied to the diversity of the
assembled germplasm and the degree of heritability for
the desired characteristic.
\
\
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';;' 20
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0
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i
'!10
'' '
i.
~~~~',,
0
A
8
Desirable Characteristic
Figure 2-Diagram showing the theoretical
effects of selection on the expression of a
genetically inherited plant characteristic. The
mean expression of the desirable characteristic in the base population is depicted by line
A, line C represents the mean expression in
the selected individuals, and line B is the level
of expression in the progenies of the selected
individuals. Amount of advancement in the
expression of the desirable characteristic
depends on the heritability of the particular
characteristic and the amount of selection
pressure (from Johnson 1986a).
Development of Screening Techniques
Even if sufficient heritable variation is present for
desirable characteristics within a breeding population,
appropriate selection procedures must be developed to
evaluate the various breeding lines for their level of
expression for the desired combination of characters.
Hanson (1972) emphasized that progress in plant breeding and selection has been impeded by the lack of reliable
screening procedures. Levitt (1964) and Cooper (1974)
underscored the importance of appropriate screening
338
\
C
Breeding Scheme
Source
nurseries----------~
Parent-progeny tests
A) Field
B) Laboratory
I
Addftional
cycles
Controlled
crosses
~
Test for release / '
A) Small plots
B) Grazing trials
Experirtierital
strains
Figure 3-A representative sequence for breeding improved range
grasses. Screening procedures play an important role in selecting
plants from the source population, evaluating progenies, identifying
superior crosses, and comparing performance of experimental
strains to released cultivars (from Johnson 1980).
the source population, evaluate the response of the progeny from the source population, isolate superior individuals from controlled crosses, or evaluate the performance
of experimental strains in comparison to released cultivars (fig. 3). These screening results can be incorporated
into a selection index, which contains results from other
field or laboratory evaluations.
(Asay and Johnson 1980, 1983; Lawrence 1963) are additional criteria that improve the predictability of seedling
establishment in some cool-season grasses. Although the
relationship between seedling emergence and improved
response to drought is somewhat indirect, rapid seedling
emergence and development have important implications
concerning adaptation to drought in cool-season grasses.
Although ability of range seedlings to grow under low
temperatures and withstand freezing would appear to
be beneficial characteristics for. selection, few breeding
programs for cool-season grasses have been selected specifically for these characteristics. Genetic variation for
seedling root growth under low temperatures has been
documented for bluebunch wheatgrass (Pseudoroegneria
spicata [Pursh] Love). Harris and Goebel (1976) evaluated root growth in 45 collections of bluebunch wheatgrass from sites as far south as Nogales, AZ, and as far
north as Fairbanks, AK. Seedling root growth at 2 oc
ranged from 1.4 to 11.9 mm at 21 days. Although differences in seed size and the seed production environment
may have explained some of this variation, significant
genetic variation may be present for root growth at low
temperature in cool-season range grasses. Additional
research concerning seedling growth under low temperatures is required.
CRESTED WIIEATGRASS
Since its introduction in the early 1900's, the crested
wheatgrasses (Agropyron cristatum [L.] Gaertn., A
desertorum [Fisch. ex Link] Schult., and A fragile [Roth]
Candargy) have been used widely for revegetating depleted rangelands in western North America (Asay 1986).
The seed and seedling relations of crested wheatgrass
have been reviewed by Johnson (1986b). Although
crested wheatgrass is generally known for its good seedling vigor and relative ease of establishment, Rogier
(1954b) found a positive relationship between seed size
and seedling vigor in A desertorum. In view of this positive relationship, Rogier (1954b) suggested that selection
for larger seeds would be a useful criterion for improving
seedling vigor in crested wheatgrass. The cultivar 'Nordan'
ofA desertorum was selected for seed size among other
characters and represented a significant improvement in
seedling performance (Rogier 1954a). Since its release,
Nordan has been used successfully on semiarid rangelands throughout the West (Rogier 1973).
Asay and Johnson (1983) evaluated the genetic variability for characters affecting stand establishment in crested
wheatgrass (A. cristatum and A. desertorum). The seedling responses examined included seedling emergence under controlled drought, seedling recovery after exposure to
Incorporation of Screening
Procedures
After appropriate selection techniques have been identified, plant improvement involves screening of the breeding lines to identify plants that have the desired combination of characteristics. These screening procedures can be
effectively used to identify superior parent plants from
339
drought, and seed weight. Evaluations involved either
168 or 175 progeny lines of crested wheatgrass, and results from the laboratory and greenhouse tests were compared with results from actual field establishment trials.
Seed weight was the characteristic most consistently correlated with field establishment. Based on these results,
seed weight, emergence from a deep planting depth, and
field agronomic performance were used to develop the
crested wheatgrass cultivar 'Hycrest' (Asay and others
1985b). Hycrest has demonstrated excellent vigor and
productivity during the early phases of stand establishment and under drought conditions (Asay and others
1986).
Russian wildrye by Berdahl and Barker (1984). Seed
weight was significantly correlated with emergence and
coleoptile length; however, the correlation decreased when
seed weight increased beyond 3 mg/seed. Based on estimates of realized heritabilities from parent-progeny relationships, they suggested that genetic progress for improved seedling vigor would most effectively be achieved
by first screening for seed size, followed by selection for
coleoptile length. Selection for dry matter yield along
with coleoptile length and emergence from a 5-cm planting
depth led to the development of the cultivar 'Mankota,'
which has demonstrated improved stand establishment
(Berdahl and others 1992).
RUSSIAN WILDRYE
SUMMARY
Russian wildrye (Psathyrostachys juncea [Fisch.]
Nevski) is a valuable forage grass on western rangelands
of North America. Once established, this grass is persistent and productive, and provides an excellent source of
high-quality forage during late summer and fall. However, Russian wildrye is noted for its poor seedling vigor
and poor stand establishment. Consequently, Russian
wildrye has not achieved its full potential as a valuable
forage grass. As a result, improved seedling establishment has been a primary objective in most Russian
wildrye breeding programs.
Lawrence (1963) evaluated several procedures for
screening Russian wildrye breeding populations for improved seedling vigor. He concluded that the most effective screening approach for Russian wildrye would be to
select breeding lines with heavy seed weight and subsequently evaluate these selected lines for their ability to
emerge from a 5-cm planting depth. These procedures
were instrumental in the development of 'Swift,' an improved cultivar of Russian wildrye (Lawrence 1979),
which has shown improved establishment vigor in field
evaluation trials.
Asay and Johnson (1980) screened 134 progeny lines of
Russian wildrye for several seedling responses including
seed weight, ability to emerge from a 7 .6-cm planting
depth, seedling emergence under controlled drought, and
seedling recovery after exposure to drought. Besides these
greenhouse and laboratory tests, the same breeding lines
were seeded at two range sites in northern Utah and southem Idaho and evaluated for their field emergence. Except
for seed weight and emergence from a 7.6-cm seeding
depth, none of the other greenhouse and laboratory data
were significantly correlated to actual field emergence.
Field emergence was more closely related to emergence
from a deep seeding depth than seed weight, suggesting
that improvement in field emergence would be more effective by selecting for emergence from a deep seeding depth.
Evaluations of ability to emerge from deep planting together with field agronomic performance resulted in the
release of the Russian wildrye cultivar 'Bozoisky-Select'
(Asay and others 1985a), which has shown marked improvement in seedling establishment under rangeland
conditions.
The genetic variability for seedling vigor and other related characteristics was studied in 30 progeny lines of
Seedlings of cool-season grasses sown on semiarid rangelands are exposed to various stresses such as competition
from aggressive annual weeds, too shallow or excessive
planting depth, drought, temperature stress, and poor
seedbed. Successful stand establishment on these areas
critically hinges on how effectively seedlings respond to
these various stresses. Seed weight, ability to emerge from
a deep planting depth, and coleoptile length have been
used successfully to improve stand establishment in
crested wheatgrass and Russian wildrye. Promise exists
for further improvements in stand establishment of these
and other cool-season grasses.
REFERENCES
Asay, K. H. 1986. Breeding strategies in crested wheatgrass. In: Johnson, K L. , ed. Crested wheatgrass: its
values, problems and myths: symposium proceedings;
1983 October 3-7; Logan, UT. Logan, UT: Utah State
University: 53-57.
Asay, K. H.; Dewey, D. R.; Gomm, F. B.; Horton, W. H.;
Jensen, K. B. 1986. Genetic progress through hybridization of induced and natural tetraploids in crested
wheatgrass. Journal of Range Management. 39:261263.
Asay, K. H.; Dewey, D. R.; Gomm, F. B.; Johnson, D. A;
Carlson, J. R. 1985a. Registration of 'Bozoisky-Select'
Russian wildrye. Crop Science. 25: 575-576.
Asay, K. H.; Dewey, D. R.; Gomm, F. B.; Johnson, D. A.;
Carlson, J. R. 1985b. Registration of 'Hycrest' crested
wheatgrass. Crop Science. 25: 368-369.
Asay, K. H.; Johnson, D. A. 1980. Screening for improved
stand establishment in Russian wild ryegrass. Canadian Journal ofPlant Science. 60: 1171-1177.
Asay, K. H.; Johnson, D. A. 1983. Genetic variability for
characters affecting stand establishment in crested
wheatgrass. Journal of Range Management. 36:
703-706.
Berdahl, J.D.; Barker, R. E. 1984. Selection for improved
seedling vigor in Russian wild ryegrass. Canadian Journal of Plant Science. 64: 131-138.
Berdahl, J.D.; Barker, R. E.; Karn, J. F.; Krupinsky, J. M.;
Haas, R. J.; Tober, D. A.; Ray, I. M. 1992. Registration of
'Mankota' Russian wildrye. Crop Science. 32: 1073.
340
Cooper, J.P. 1974. The use of physiological criteria in
grass breeding. Aberystwyth, Wales: Welsh Plant
Breeding Station Report: 95-102.
Hanson, A. A. 1972. Breeding of grasses. In: Youngner,
V. B.; McKell, C. M., eds. The biology and utilization of
grasses. New York: Academic Press: 36-52.
Harper, J. L. 1977. Population biology of plants. London:
Academic Press. 892 p.
Harris, G. A.; Goebel, C. J. 1976. Factors of plant competition in seeding Pacific Northwest bunchgrass ranges.
Bull. 820. Pullman, WA: Washington State Agricultural
Experiment Station. 22 p.
Hunt, 0. J.; Miller, D. G. 1965. Coleoptile length, seed
size, and emergence in intermediate wheatgrass (Agropyron intermedium (Host) Beauv.). Agronomy Journal.
57: 192-195.
Johnson, D. A 1980. Improvement of perennial herbaceous plants for drought-stressed western rangelands.
In: Turner, N.C.; Kramer, P. J., eds. Adaptation of perennial herbaceous plants for drought-stressed western
rangelands. New York: John Wiley and Sons: 419-433.
Johnson, D. A. 1986a. Improved rangeland species: a
physiological perspective. In: Joss, P. J.; Lynch, P. W.;
Williams, 0. B., eds. Rangelands: a resource under
siege. Canberra: Australian Academy of Science:
444-446.
Johnson, D. A. 1986b. Seed and seedling relations of
crested wheatgrass: a review. In: Johnson, K L., ed.
Crested wheatgrass: its values, problems and myths:
Symposium proceedings; 1983 October 3-7; Logan, UT.
Logan, UT: Utah State University: 65-90.
Johnson, D. A; Asay, K. H. 1993. Viewpoint: selection for
improved drought response in cool-season grasses. Journal of Range Management. 46: 194-202.
Johnson, D. A; Rumbaugh, M. D.; Asay, K. H. 1981. Plant
improvement for semiarid rangelands: possibilities for
drought resistance and nitrogen fixation. Plant and
Soil. 58: 279-303.
Kneebone, W. R. 1972. Breeding for seedling vigor. In:
Youngner, V. B.; McKell, C. M., eds. The biology and
utilization of grasses. New York: Academic Press:
90-100.
Lawrence, T. 1963. A comparison of methods of evaluating
Russian wild ryegrass for seedling vigor. Canadian
Journal of Plant Science. 43:307-312.
Lawrence, T. 1979. Swift, Russian wild ryegrass. Canadian Journal of Plant Science. 59: 515-518.
Levitt, J. 1964. Drought. In: Forage plant physiology and
soil-range relationships. Publ. 5. Madison, WI: American Society of Agronomy: 57-66.
McKell, C. M. 1972. Seedling vigor and seedling establishment. In: Youngner, V. B.; McKell, C. M., eds. The biology and utilization of grasses. New York: Academic
Press: 74-89.
Plummer, A. P. 1943. The germination and early seedling
development of twelve range grasses. Journal of the
American Society of Agronomy. 35: 19-34.
Rogier, G. A. 1954a. Nordan crested wheatgrass. Bull. 16.
Fargo, ND: North Dakota Agricultural Experiment Station: 150-152.
Rogier, G. A. 1954b. Seed size and seedling vigor in
crested wheatgrass. Agronomy Journal. 46:216-220.
Rogier, G. A. 1973. The wheatgrasses. In: Heath, M. D.;
Metcalfe, D. S.; Barnes, R. F., eds. Forages: the science
of grassland agriculture. Ames, lA: Iowa State University Press: 221-230.
Stoddart, L. A.; Smith, A. D.; Box, T. W. 1975. Range
management. New York: McGraw-Hill Book Co. 532 p.
TeKrony, D. M.; Egli, D. B. 1991. Relationship of seed
vigor to crop yield: a review. Crop Science. 31:816-822.
341