Warm-season Forage Grasses Research Articles

Breeding for reduced seed dormancy to domesticate new grass species.

Introducing new grass species into cultivation has long been proposed as beneficial to increase the sustainability and diversity of productive systems. However, wild species with potential tend to show high seed dormancy, causing slow, poor, and unsynchronized seedling emergence. Meanwhile, domesticated species, such as cereals, show lower seed dormancy, facilitating their successful establishment. In this work, we conduct a review of phenotypic variation on seed dormancy and its genetic and molecular basis. This quantitative and highly heritable trait shows phenotype plasticity which is modulated by environmental factors. The level of dormancy depends on the expression of genes associated with the metabolism and sensitivity to the hormones abscisic acid (ABA) and gibberellins (GA), along with other dormancy-specific genes. The genetic regulation of these traits is highly conserved across species. The low seed dormancy observed in cereals and some temperate forages was mostly unconsciously selected during various domestication processes. Emphasis is placed on selecting materials with low seed dormancy for warm-season forage grasses to improve their establishment and adoption. Finally, we review advances in the domestication of dallisgrass, where seed dormancy was considered a focus trait throughout the process.

Differential Physiological, Transcriptomic, and Metabolomic Responses of Paspalum wettsteinii Under High-Temperature Stress.

Global warming has far-reaching effects on plant growth and development. As a warm-season forage grass, Paspalum wettsteinii is highly adaptable to high temperatures. However, the response mechanism of P. wettsteinii under high-temperature stress is still unclear. Therefore, we investigated the physiological indicators, transcriptome and metabolome of P. wettsteinii under different heat stress treatments. Plant height, the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and the contents of soluble sugar, proline, chlorophyll a, and chlorophyll b increased and then decreased, while the malondialdehyde (MDA) content decreased and then increased with increasing heat stress. Transcriptomic analysis revealed that genes related to energy and carbohydrate metabolism, heat shock proteins (HSPs), and transcription factors (TFs), secondary metabolite biosynthesis and the antioxidant system significantly changed to varying degrees. Metabolomic analysis showed that only free fatty acids were downregulated, while amino acids and their derivatives, organic acids, flavonoids, and sugars were both up- and downregulated under heat stress. These combined analyses revealed that growth was promoted at 25–40°C, while at 45°C, excess reactive oxygen species (ROS) damage reduced antioxidant and osmoregulatory effects and inactivated genes associated with the light and electron transport chains (ETCs), as well as damaged the PS II system and inhibited photosynthesis. A small number of genes and metabolites were upregulated to maintain the basic growth of P. wettsteinii. The physiological and biochemical changes in response to high-temperature stress were revealed, and the important metabolites and key genes involved in the response to high temperature were identified, providing an important reference for the physiological and molecular regulation of high-temperature stress in plants.

Seed yield potential improvement through breeding in

Context Panicum coloratum is a relatively undomesticated small-seeded warm-season forage grass. Seed shattering, an extended reproductive period and non-synchronic seed maturation limit harvested seed yields. Low seed quantity and quality hinder pasture establishment and discourage its use. Aims To assess whether seed yield potential could be improved by breeding, we sought to measure variability in traits related to seed production including phenotypic plasticity in response to environmental cues, and estimated narrow-sense heritability, prospective genetic gain after selection and co-heritabilities in seed yield components. Methods Seed retention (SR), number of panicles (PN), seed number per panicle (SN) and seed weight (SW) were measured in plants growing in the field. Clonal replicates of 13 genotypes were assessed in 2007 and 2010 and half-sib families derived from these genotypes were measured in 2010. Key results Phenotypic variability among genotypes was related to genetic factors for all measured variables. Two broad groups of accessions showing differences in SR were studied. Phenotypic plasticity in SR differed among genotypes and was negatively related to levels of SR, implying that stable high-SR genotypes could be selected in a breeding program. Maximum narrow-sense heritabilities were 0.89 and 0.41 for SN and SR, respectively, with estimated gains after selection around 30%. The best results were achieved if selecting for SR at 3–5 weeks after anthesis. Low genetic correlations and extremely low co-heritabilities between other characters and seed yield components discourage the possibility of indirect selection. Conclusion Moderate increases in seed production potential may be achieved after selection for SN, SW and SR in P. coloratum var. makarikariense. Implications Improvements in SR and other seed yield components would facilitate harvest, increase yield and consequently increase profitability to growers and stimulate pasture adoption by farmers.

Prediction of the nutritional value of grass species in the semiarid region by repeatability analysis

Abstract: The objective of this work was to estimate the repeatability (r) and the number of samples required to measure the nutritional value of four warm-season forage grasses growing in a semiarid region. The grasses evaluated were Urochloa mosambicensis, Cenchrus ciliaris, Digitaria pentzii, and Megathyrsus maximus. Evaluations occurred under two forage management conditions: stockpiling and grazing. Hand-plucked forage samples were analyzed for dry matter (DM), crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), lignin, and in vitro DM digestibility (IVDMD). Four methods were used to estimate r and the number of samples required: analysis of variance, method of principal components based on the covariance (PCCOV) and the correlation (PCCOR) matrices, and structural analysis (EVCOR). Species were compared by the probability of the difference using the t-test. The method PCCOV presents the highest coefficient of repeatability and, therefore, a lower number of samples required. Lignin is the trait that have the highest number of samples required. In terms of qualitative traits, D. pentzii and M. maximus show the best forage qualities among the species evaluated.

Identification of Endogenous Reference Genes for RT-qPCR Expression Analysis in Urochloa brizantha Under Abiotic Stresses

Urochloa brizantha is one of the most important warm season forage grasses in tropical countries. Despite its importance, there are few studies on gene expression in this species under stressful conditions. Real-time (RT-qPCR) is an accurate technique for gene quantification analysis, but reference genes must be validated under the same conditions used to assess the expression of the target genes. Here, we evaluated the stability of nine reference genes: Actin 12, Eukaryotic initiation factor 4 A, Elongation factor-1 alpha, FTSH protease 4, U2 auxiliary fator, Succinol Co-enzyme A, Tubulin alfa-5, Tubulin beta-6, Ubiquitin conjugating enzyme. Total RNA was extract from leaf tissues of U. brizantha subjected to 6, 12 and 24 h of cold and heat stresses (10 and 45 °C, respectively), and drought, including moderate (−0.5 to −0.7 MPa), severe (−1.1 to −1.8 MPa) and recovery after re-watering. The RefFinder web-based tool was used to rank the most stable reference genes for each stress. Elongation factor-1 alpha, Elongation factor-1 alpha or Ubiquitin conjugating enzyme, and Eukaryotic initiation factor 4 A were the most stable genes for heat, cold and drought stress, respectively. The expression of Rubisco large subunit gene was normalized against the most stable gene selected by ReFfinder for each stress.

The Invasive Legacy of Forage Grass Introductions into Florida

Exotic African warm-season forage grasses were first introduced into the Americas in the 16th century, and have become invasive in many areas. In Florida, 16 exotic grasses are considered invasive, with the majority originating in Africa and introduced as forages. The high propensity of Africa warm-season grasses to become invasive may be related to the same characteristics that are associated with their value as forages, including adaptability to a wide range of abiotic conditions, rapid establishment, persistence in the environment with minimal husbandry, high productivity under grazing pressure, and adaptation to disturbance. The majority of African warm-season grasses in Florida reproduce vegetatively, a trait known to be associated with invasiveness, and many have been widely planted leading to high propagule pressure and opportunities to invade a variety of niches. In spite of a long history of introduction and promotion in Florida, few African forage grasses are in use today, while many have become invasive. The benefit/cost ratio appears to be tilted in the direction of environmental and economic costs, with minimal benefits. We support newly enacted restrictions on the importation of potentially invasive plants into the USA, and suggest the establishment of a more comprehensive and transparent system for tracking past and future introductions.

Agrobacterium tumefaciens-mediated transformation of big bluestem (Andropogon gerardii Vitman)

Big bluestem (Andropogon gerardii Vitman) is native to the Great Plains of North America and is an important warm-season forage and ornamental grass. Recently it has been proposed as one of the more ideal biomass producers for cellulosic ethanol production due to its high biomass yield and low input needs. A robust genetic transformation protocol is needed for germplasm improvement or functional genomics studies in big bluestem. In the present study we report, for the first time the establishment of a reproducible Agrobacterium-mediated transformation protocol for big bluestem. Mature seeds of a big bluestem cultivar Bison were cultured for producing embryogenic calli, which were then used for infection by the Agrobacterium tumefaciens strain AGL1 harboring either the binary vector pTF101.1, which carries the glufosinate resistance (bar) gene or a modified binary vector pMDC32 which carries the hygromycin resistance gene (hpt). Glufosinate ammonium at 6 mg L−1 or hygromycin B at 250 mg L−1 was used effectively to select for resistant callus followed by lowered concentrations of both during regeneration and rooting. Based on PCR test alone or in combination with herbicide leaf painting, the overall transformation frequency was 2.8–3.6 % by using the pTF101.1 vector and 2.4–3.3 % by using the modified pMDC32 vector, both of which are comparable to transformation frequencies reported for other grasses. PCR test showed that all Basta®-resistant plants following the leaf painting contain the bar gene and subsequent Southern blot analysis confirmed that the all tested transgenic plants resulted from independent transgenic events.

The Present Status of C<sub>4</sub> Tropical Grasses Breeding and Molecular Approaches

Tropical grasses have been widely utilized as warm-season grasses in the warm temperate zone since the early 20th century because of their high yields as well as for perennial forages in their native tropical areas. The high yield of tropical grasses is mainly due to C4 photosynthesis. However, the soaring demands for animal production sparked by economic development in tropical countries mean genetic improvement of such grasses is urgently needed. Considerable breeding efforts have been made to create and develop new tropical grass cultivars, although direct selection from natural populations remains the main method used for breeding. Cross-breeding has not proliferated due to a lack of genetic information concerning the polyploidy, high sterility, outcrossing, and apomixis of these grasses, although several of these difficulties are starting to be resolved by advanced research using molecular biology tools. These tools are an effective means of achieving genetically improving of tropical grasses, and further development is anticipated. In this review, achievements in the improved guineagrass, brachiariagrass, sorghum, and zoysiagrass are introduced and discussed. Discipline: Biotechnology, Genetic resources, Plant breeding Additional key words: brachiariagrass, forage, guineagrass, sorghum, zoysiagrass *Corresponding author: e-mail triticum@affrc.go.jp Received 21 February 2014; accepted 10 October 2014. Introduction Tropical grasses have been widely utilized as warmseason forage grasses in warm temperate regions and as perennial forage grasses in tropical areas since the early 20th century, mainly because of their high yields. Some of these grasses represent familiar species whose value as forage has only recently been recognized (Moser et al. 2004). As a typical example, guineagrass is a valuable forage grass with numerous names given to it by various tribes familiar with it in its natural habitat, and brachiariagrass is still not utilized willingly in its area of origin. Most of these grasses have extremely high yields because of C4 photosynthesis. Demand for animal production in tropical countries is currently soaring due to economic development there, which is one of the major factors driving the development of new tropical grass cultivars. Despite considerable breeding efforts to create and develop new tropical grass cultivars, direct selection from natural populations remains the main breeding method used (Moser et al. 2004), with some notable exceptions. Some efforts have also been made to perform crossing in guineagrass (Bhandari et al. 2011) and brachiariagrass (Felismino et al. 2010, Miles et al. 2004) species, but their polyploidy, high sterility, outcrossing, and apomixis hinder the development of new cultivars. Some breeding progress has been made using molecular biology methods in addition to conventional methods (Ebina et al. 2005, Tsuruta et al. 2011). These molecular tools are particularly powerful for obtaining information on their genetic information and inheritance, which has usually been insufficient to improve the key traits of tropical grasses. For these reasons, further developments of molecular tools in these species hold great promise.

Plant Regeneration from Young Shoot of Nilegrass (Acroceras macrum)

To optimize the method for embryogenic callus induction and plant regeneration from young shoot explants of Nilegrass (a warm-season forage grass species), young shoots were cultured onto LS medium supplemented with 0.5, 1, 3 and 5 mg/l 2,4-D, 0.1 mg/l BA, 4 mg/l Thiamine-HCl,100 mg/l, α-ketoglutaric acid, 30 g/l sucrose and 2.6 g/l phytagel for 8 weeks. The highest callus formation and embryogenic callus induction was obtained on LS medium supplemented with 1 mg/l 2,4-D (27.50% and 13.75%, respectively). The embryogenic nature of the compact structure was confirmed by scanning electron microscopy. The embryogenic calli were cultured on LS media supplemented with 0.5, 1, 3 and 5 mg/l BA, 3% sucrose and 2.6 g/l phytagel. After 8 weeks of culture, the highest regeneration percentages (100%) was obtained on 5 mg/l BA. The plantlets were successfully transferred to grow in the soil.

Expression of CoQ10-producing ddsA transgene by efficient Agrobacterium-mediated transformation in Panicum meyerianum

Panicum meyerianum Nees is a wild relative of Panicum maximum Jacq. (guinea grass), which is an important warm-season forage grass and biomass crop. We investigated the conditions that maximized the transformation efficiency of P. meyerianum by Agrobacterium infection by monitoring the expression of the β-glucuronidase (GUS) gene. The highest activities of GUS in calli were achieved by the co-cultivation of plants with Agrobacterium at 28°C for 6 days. We transferred the ddsA gene, which encodes decaprenyl diphosphate synthase and is required for coenzyme Q10 (CoQ10) synthesis, into P. meyerianum by using our optimized co-cultivation procedure for transformation. We confirmed by PCR and DNA gel blot hybridization that all hygromycin-resistant plants retained stable insertion of the hpt and ddsA genes. We also demonstrated strong expression of S14:DdsA protein in the leaves of transgenic P. meyerianum. Furthermore, we showed that transgenic P. meyerianum produced CoQ10 at levels 11–20 times higher than that of non-transformants. By comparison, the CoQ9 level in transgenic plants was dramatically reduced. This is the first report of efficient Agrobacterium-mediated transfer of a foreign gene into the warm-season grass P. meyerianum.

난지형 목초 기니아그라스의 효율적인 캘러스 유도 및 식물체 재분화

Guineagrass (Panicum maximum Jacq.) is an important warm-season forage grass as well as biomass crop. It has both sexual and asexual mode of reproduction (apomictic) depending on cultivar. We developed efficient plant regeneration system for an apomictic (cv. Natsukaze) and a non-apomictic (Noh-PL1) guineagrass by optimizing the level of L-proline in the callus induction and that of AgNO3 in plant regeneration medium. Among the L-proline concentrations tested, the best callus induction was achieved by using 2g/L L-proline in both the genotypes. Immature embryos proved to be the best explant source for tissue culture of guineagrass. The highest frequency of shoot regeneration was obtained on MS plant regeneration medium supplemented with 2 mg/L AgNO3. These results provide a foundation for efficient tissue culture and genetic improvement of guineagrass. (Key words : L-proline, AgNO3, Immature embryo, Guineagrass, Shoot regeneration)

Particle inflow gun-mediated transformation of multiple-shoot clumps in rhodes grass ( Chloris gayana)

Rhodes grass (Chloris gayana) is one of the most important warm-season forage grasses. It is cultivated in tropical and subtropical parts of the world and is mostly used for grazing and hay production. We have established a particle-bombardment transformation protocol for rhodes grass using multiple-shoot clumps (MSCs) as the target tissue. A vector pAHC25 containing a herbicide-resistance gene (bar) together with the beta-glucuronidase (GUS) gene was used in transformation experiments. The most efficient recovery of bialaphos-resistant tissue was achieved when the bombarded MSCs were first cultured for 15 d on bialaphos-free medium before being subjected to selection pressure. The resistant tissues regenerated transgenic plants that displayed GUS gene expression. Under optimized conditions, 251 target pieces yielded 46 transgenic plants from 4 independent transgenic lines.

Occurrence of the Wheat Stem Maggot, Meromyza americana Fitch (Diptera: Chloropidae), in Intermediate Wheatgrass, Thinopyrum intermedium (Host) Barkworth and D. R. Dewey (Poaceae), in Oklahoma1

The wheat stem maggot is primarily an economic pest of wheat, Triticum aestivum L.; barley, Hordeum vulgare L.; and cereal rye, Secale cereale L. (Poaceae) (Gilbertson, 1925; Allen and Painter, 1937; Rockwood et al., 1947). The larva of the wheat stem maggot enters the culm above the terminal node and feeds within the culm. Consequently, the developing inflorescence withers and dies and turns white in color. The aborted inflorescences are very noticeable among non-infested inflorescences. In Oklahoma, wheat stem maggot infestations have been reported to occur in seed production fields of bermudagrass, Cynodon dactylon var. dactylon (L.) Pers., and weeping love grass, Eragrostis curvula (Schrad.) Nees (Arnold and Ahring, 1987; Kindler et al., 1989). These were the first reported cases of wheat stem maggot to economically impact important warm-season forage grasses. Kindler et al. (1989) reported the percentage of aborted inflorescence in weeping lovegrass ranged from 3.2 to 22.6%. Intermediate wheatgrass, Thinopyrum intermedium (Host) Barkworth and D.R. Dewey, is an introduced forage grass that is used for pasture and hay for livestock in the Northern Great Plains, the Central and Southern High Plains, and much of the western United States. In the Southern Plains, research has shown that perennial, cool-season forage grasses do not persist through prolonged drought. Gillen and Berg (2005) reported a 95% reduction in stand due to drought where precipitation from September 2001 through May 2002 measured 62% of normal. Seeds from surviving plants from pastures used by Gillen and Berg were harvested in June 2002 and increased at the USDA-ARS Southern Plains Range Research Station, Woodward, Oklahoma. It was anticipated that progeny from these plants would have increased tolerance to drought. In late June 2006, aborted inflorescences of intermediate wheatgrass were found in a seed production block at Woodward. Aborted inflorescences were collected from the plot on 30 June, placed in Erlenmeyer flasks containing about 300 ml of tap water, and caged by placing them in a clear plastic bag with a nylon mesh screen on two sides to determine which insect was responsible (Kindler et al., 1989). Adult flies emerged 15–20 days later and were identified as wheat stem maggot using the keys of Sabrosky (1935) and Fedoseeva (1971). The percentage of aborted inflorescences was determined from randomly sampling 10 quadrats (30 3 30 cm) and ranged from 10 to 28%. Accordingly, the wheat stem maggot was confirmed as a pest of intermediate wheatgrass in Oklahoma which is a new host record. Voucher specimens were deposited at the K. C. Emerson Entomological Museum, Oklahoma State University, Stillwater.

CATERPILLAR (LEPIDOPTERA: NOCTUIDAE) FEEDING ON PASTURE GRASSES IN CENTRAL FLORIDA

Abstract Stargrasses (Cynodon nlemfuensis Vanderyst var. nlemfuensis) and bermudagrasses (C. dactylon (L.) Persoon) are important warm-season forage grasses, with several cultivars developed for conditions found in central and southern Florida. Major insect pests of these grasses include grass loopers (Mocis spp.) and fall armyworm (Spodoptera frugiperda (J. E. Smith)), which annually may impose economic losses for beef cattle and hay producers. Population studies conducted during a 3-year period showed that both species had similar profiles with respect to larval population seasonality but not abundance. Plot studies with 4 stargrass and 4 bermudagrass lines showed that higher grass looper populations were found in stargrasses than bermudagrasses. Laboratory studies found grass loopers and fall armyworm larvae generally developed faster with larger weights on lines of stargrass than lines of bermudagrass. The two fall armyworm host strains also can differ substantially in their larval weight, development...

A genetic map of tetraploid Paspalum notatum Flügge (bahiagrass) based on single-dose molecular markers

Paspalum notatum Flügge is a warm-season forage grass with mainly diploid (2n = 20) and autotetraploid (2n = 40) representatives. Diploid races reproduce sexually and require crosspollination due to a self-incompatible mating system, while autotetraploids reproduce by aposporous apomixis. The objectives of this work were to develop a genetic linkage map of Paspalum notatum Flügge at the tetraploid level, identify the linkage/s group/s associated with apomixis and carry out a general characterization of its mode of inheritance. A pseudo test-cross F1 family of 113 individuals segregating for the mode of reproduction was obtained by crossing a synthetic completely sexual tetraploid plant (Q4188) as female parent with a natural aposporous individual (Q4117) as pollen donor. Map construction was based on single-dose markers (SDAFs) segregating from both parents. Two linkage maps (female and male) were constructed. Within each map, homologous groups were assembled by detecting repulsion-phase linked SDAFs. Putative Q4188 and Q4117 homolog groups were identified by mapping shared single dose markers (BSDF). The Q4188 map consisted of 263 markers distributed on 26 co-segregation groups over a total genetic distance of 1.590.6 cM, while the Q4117 map contained 216 loci dispersed on 39 co-segregation groups along 2.265.7 cM, giving an estimated genome coverage of 88% and 83%, respectively. Seven and 12 putative homologous chromosomes were detected within Q4188 and Q4117 maps, respectively. Afterward, ten female and male homologous chromosomes were identified by mapping BSDFs. In the Q4117 map, a single linkage group was associated with apospory. It was characterized by restriction in recombination and preferential chromosome pairing. A BPSD marker mapping within this group allowed the detection of the female homolog and the putative four male groups of the set carrying apospory.

Forage production of tropical grasses under extended daylength at subtropical and tropical latitudes

Decreased growth of warm-season forage grasses during subtropical winters has been shown to be a response to short-daylength during those months. The objective of this research was to evaluate the influence of short-daylength on growth of forage grasses in low latitude locations. Three grasses (Argentine bahiagrass, Paspalum notatum Flügge; Common guineagrass, Panicum maximum Jacq.; Tifton-85 bermudagrass, Cynodon spp. Pers.) were grown at three locations (south Florida, Puerto Rico, and St. Croix) under extended (15 h) and natural daylength during 2 years. Plots were harvested at 5-week (October–February) and 4-week (March–April) intervals to measure dry matter (DM) yield and nutritive value of the herbage. Daylength effects were found on DM harvested for all grasses in south Florida ( P < 0.01). At that location, grasses exposed to increased daylength averaged a 44% increase in DM harvested compared to those grown under natural daylength. Daylength effects were consistent for bahiagrass at the other two locations as well. However, guineagrass and bermudagrass did not respond to extended daylength in Puerto Rico and St. Croix. These results showed that bahiagrass is capable of producing additional forage during the cool season at all locations tested if sensitivity to photoperiod is genetically removed or attenuated.

Optimizing embryogenic callus production and plant regeneration from 'Tifton 9' bahiagrass seed explants for genetic manipulation

Bahiagrass (Paspalum notatum Flugge) is a warm season forage grass widely cultivated in southeastern U.S. and South America. The cultivar Tifton 9 has several desirable characteristics such as high forage yield, more vigor at the seedling stage, etc.; but its forage quality is very low. As an initial step for future genetic manipulations to improve its forage characteristics, we have optimized in vitro culture conditions for plant regeneration. In this report, we describe an efficient method for embryogenic callus induction and plant regeneration from bahiagrass (cv. Tifton 9) seed explants, which are readily available and easy to manipulate, compared to other explant sources reported in the literature. Murashige and Skoog (MS) medium containing 30 μM dicamba and 5 μM 6-benzyladenine (BA) was optimal for callus induction and growth. Out of 9734 seeds cultured, 65.7% germinated and 21.4% produced embryogenic callus on this medium. Shoot formation was best when embryogenic calluses induced in this medium were transferred to MS medium supplemented with 5 μM BA and 1 μM gibberellic acid with 1640 plantlets formed per gram fresh weight of callus tissue. When transferred to hormone-free SH medium, shoot systems produced well-developed root systems. The resulting plantlets grew normally produced viable seeds when transferred to soil in the greenhouse. Histochemical staining for GUS activity arising from transient expression of the introduced uidA (β-glucuronidase) gene indicated that bahiagrass embryogenic callus produced by this method is suitable for gene transfer via biolistic bombardment; and it can serve as a good target tissue for future genetic manipulations to improve the forage quality of bahiagrass (cv. Tifton 9).

Switchgrass Growth and Development: Water, Nitrogen, and Plant Density Effects

Switchgrass (Panicum virgatum L.), an important component of the tallgrass prairie, is a productive warm-season forage grass. Interest in growing switchgrass for alternative uses has raised questions about resource use during production. The objective of our study was to examine how resource inputs affected interspecific plant competition in switchgrass. 'Alamo' switchgrass was established from seed in outdoor lysimeters in May 1993 and grown under 22 or 112 kg N ha(-1), and under field capacity or water-deficit conditions until August 1994. Plant spacing varied systematically from 10 to 70 cm. Plants were harvested in late summer each year and individual plant dry weight, tiller number, leaf area, and morphological development stage were measured. Soil moisture tensions below -45 kPa reduced switchgrass photosynthetic rates and xylem pressure potential. As plant spacing increased, tiller number, leaf area, plant dry weight, and morphological development stage increased. Plant dry weight and tiller number in the establishment year was not affected by N input. Established plants in 1994, however, responded to high N input at low plant densities with 50 to 100% greater leaf area and up to 3-fold greater plant dry weight compared to the low-N treatment. The increased plant dry weight at high N input resulted from increased individual tiller weight and not increased tiller number. Our data indicate that competitive responses of switchgrass plants at high plant densities were controlled by competition for aboveground resources, as plant yield and morphology at high densities were not affected by water or N inputs. DOI:10.2458/azu_jrm_v53i2_sanderson

Switchgrass growth and development: water, nitrogen, and plant density effects

Switchgrass (Panicum virgatum L.), an important component of the tallgrass prairie, is a productive warm-season forage grass. Interest in growing switchgrass for alternative uses has raised questions about resource use during production. The objective of our study was to examine how resource inputs affected interspecific plant competition in switchgrass. 'Alamo' switchgrass was established from seed in outdoor lysimeters in May 1993 and grown under 22 or 112 kg N ha(-1), and under field capacity or water-deficit conditions until August 1994. Plant spacing varied systematically from 10 to 70 cm. Plants were harvested in late summer each year and individual plant dry weight, tiller number, leaf area, and morphological development stage were measured. Soil moisture tensions below -45 kPa reduced switchgrass photosynthetic rates and xylem pressure potential. As plant spacing increased, tiller number, leaf area, plant dry weight, and morphological development stage increased. Plant dry weight and tiller number in the establishment year was not affected by N input. Established plants in 1994, however, responded to high N input at low plant densities with 50 to 100% greater leaf area and up to 3-fold greater plant dry weight compared to the low-N treatment. The increased plant dry weight at high N input resulted from increased individual tiller weight and not increased tiller number. Our data indicate that competitive responses of switchgrass plants at high plant densities were controlled by competition for aboveground resources, as plant yield and morphology at high densities were not affected by water or N inputs.

Quantitative Measurement of Fiber Fractions of Cool- and Warm-Season Grass Herbage Using Cell-Wall-Degrading Enzymes

Quantitative in vitro methods using commercial cellulase (CEL), pectinase (PECT), and hemicellulase (HCEL) preparations were developed to simplify prediction of digestibility of cool- and warm-season forage grasses. Samples of orchardgrass (Dactylis glomerata L. var. Pennlate), tall fescue (Festuca arundinacea Schreb. var. KY 31) (cool-season grasses), big bluestem (Andropogon gerardi Vitman var. NY 1145), and switchgrass (Panicum virgatum L. var. KY 1625) (warm-season grasses) were taken at advancing stages of maturity. Isolated cell-wall material (CWM) was prepared by repetitively extracting lyophilized, ground tissue with aqueous and organic solvents. Relative solubilities of CWM digested individually with CEL, HCEL, or PECT were 100:30:40, respectively. When enzyme preparations were used sequentially, the influence of CEL, HCEL, and PECT on CWM solubility depended on the order in which the enzyme preparations occurred in the sequence. The fraction of CWM solubilized with CEL was similar to that obtain...