| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK, Canada S7N 0X2
Corresponding author (ferdinandezy{at}em.agr.ca)
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Abbreviations: ADF, acid detergent fiber • CP, crude protein • IVDMD, in vitro dry matter digestibility • NDF, neutral detergent fiber
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Changes occur to the chemical composition of plant parts and the sward structure of grasses with advancing maturity. These changes cause the nutritive value of cool-season grasses to decrease with advancing maturity. This can be attributed to a decrease in forage digestibility and crude protein concentration (Kilcher and Troelsen, 1973; Buxton and Marten, 1989; Hockensmith et al., 1997), and an increase in fiber and lignin concentration (Sanderson and Wedin, 1989; Belanger and McQueen, 1996; Hockensmith et al., 1997). Apart from chemical changes, morphological changes such as leaf/stem ratio of the plant have been observed to change with advancing maturity causing the decline of whole-plant nutritive value (Ugherughe, 1986).
The changes in nutritive value of plant parts such as leaves and stems influence the whole-plant nutritive value at all stages of maturity. At the vegetative stage, nutritive value of smooth bromegrass leaves and stems may be similar, but a rapid decline of stem nutritive value after heading leads to the decrease in whole-plant forage nutritive value (Pritchard et al., 1963; Kilcher and Troelsen, 1973; Buxton and Marten, 1989). Both leaves and stems of smooth bromegrass decrease in nutritive value with advancing plant maturation. The decline of smooth bromegrass nutritive value has been attributed to stems having a higher lignin content than leaves (Sosulski et al., 1960). Deposition of cell wall lignin occurs more rapidly in stems than leaves as maturity advances (Kilcher and Troelsen, 1973) resulting in lower in vitro dry matter digestibility of stems compared with leaves (Pritchard et al., 1963).
Smooth bromegrass nutritive value has been studied extensively, but the nutritive value of meadow bromegrass and hybrid bromegrasses has only recently been described. At the vegetative stage, meadow bromegrass showed slightly lower protein and higher fiber concentrations, but these differences became less evident at later stages of growth (Knowles et al., 1993). At early stages of development, leaf ADF concentrations of smooth bromegrass and a hybrid bromegrass line (S-9044) were higher than meadow bromegrass; however, at later stages, the stem ADF of meadow bromegrass was lower than the hybrid bromegrass line (Baron et al., 2000). Even though these are all cool-season grasses, unique morphological and growth characteristics associated with each bromegrass type may result in differences in forage nutritive value. At the vegetative stage, the morphology of these grasses appears to be similar; however, as the grasses reached the heading stage, morphological differences were evident (Ferdinandez and Coulman, 2000). A majority of the tillers of smooth bromegrass developed seed heads, whereas fewer of the tillers in meadow bromegrass reached this stage of development. An intermediate number of tillers of the hybrid bromegrass developed seed heads. Morphologically, leaf blades of smooth bromegrass and the hybrid bromegrasses appeared to be similar in width; however, the hybrids had pubescence on the leaf blades. Meadow bromegrass has long narrow leaves with pubescence on the leaf blade. In view of these morphological differences in the leaf and stem, whole-plant nutritive value may vary with advancing maturity in each grass.
Meadow and smooth bromegrass differ in nutritive value (Knowles et al., 1993). Our hypothesis is that the hybrid populations are intermediate in nutritive value to meadow and smooth bromegrass; however, different morphological criteria used in the selection of each hybrid may have changed the nutritive value accordingly. The objective of this study was to compare meadow bromegrass, smooth bromegrass, and three hybrid bromegrass populations for NDF, ADF, and CP concentration of leaves, stems, and whole-plant at the vegetative, heading, and anthesis stages of development.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Field plots were located at the Agriculture and Agri-Food Canada Research Center farm in Saskatoon, SK (52°07' lat, 106°38' long). The soil type was Sutherland clay loam (Typic Haploboroll). The two parental species and the three hybrid populations were seeded in the spring of 1993 in four row plots 1.25 by 6 m. Seeding rates were 16 kg ha-1 for smooth bromegrass, S-9073, and S-9183 and 20 kg ha-1 for meadow bromegrass and S-9197. The seeding rates were adjusted to reflect the seed size and germination percentage. Each fall 100 kg ha-1 N and 46 kg ha-1 P2O5 fertilizers were broadcast applied. The experimental design was a randomized complete block with five replicates.
Data Collection
Samples were collected in 1996 and 1997 at the vegetative, heading, and anthesis stages of development of each entry according to the scale described by Moore et al. (1991). Meadow bromegrass reached the heading and anthesis stages of development 10 to 14 d prior to smooth bromegrass and the three hybrid populations. Samples were collected when 50% of the tillers in a plot reached the appropriate development stage. Samples were obtained by clipping 400 tillers randomly selected throughout the plot to a height of 3 cm above the ground. Each sample at each growth stage was separated into leaf blade, and stem (including leaf sheath and panicles if present) fractions. A portion of the plant material was not separated and was used for whole plant analysis. In 1996, plant separation was not carried out at the vegetative stage because of insufficient plant material being sampled, thus only whole plant samples were analyzed. Each of the plant fractions was placed in a paper bag and dried at 60°C in a forced-air oven for 48 h to obtain a dried sample with minimum chemical changes (Shenk and Westerhaus, 1994). The dried plant fractions were ground in a Wiley mill followed by a Udy mill to pass through a 1-mm screen, and stored in airtight plastic bags.
Chemical Analyses
Fiber Analysis
Ground samples were analyzed sequentially for NDF and ADF concentrations using the Ankom200/200 fiber analyzer (ANKOM Technology Corporation, New York). The sealed filter bags, including the samples, were placed in the reservoir of the fiber analyzer, which contained NDF solution (Sodium lauryl sulphate), and incubated for 1 h at 100°C. Following incubation the samples were washed with hot water (90–100°C) and heat-stable alpha-amylase. Finally the bags were washed in acetone and dried at 105°C. After drying and recording the weights to determine NDF, the bags were placed back in the reservoir of the fiber analyzer, containing ADF detergent fiber solution (Cetyltrimethyl-ammonium bromide). The samples were incubated for a 1-h period at 100°C and washed three times with hot water (90–100°C). Samples were dried first in acetone, followed by drying in an oven at 105°C.
Protein Analysis
Total nitrogen concentration was determined by the micro-Kjeldahl method with an auto analyzer (Technicon Autoanalyzer 11, Pulse Instrumentation Ltd., Saskatoon, SK.) (Gehrke et al., 1968). Crude protein (CP) concentration (g kg-1) was determined by the following formula: total N concentration x 0.625 x 1000.
Statistical Analysis
The treatments were pure-seeded stands of the two parental cultivars and the three hybrid populations. Split-plot in time (Steel and Torrie, 1980) analysis of variance was carried out, with cultivars as main plot and years as sub-plot, to determine the cultivar x year interaction. All effects, except for replications, were considered fixed. The year x cultivar interaction was tested by comparing the mean squares for this effect against the mean square of residual error (error b). The year effect was significant for number of variables, so for simplicity of presentation, years were analyzed separately for all variables. The treatment effects (parental cultivars and hybrid populations) at each growth stage for each plant part were evaluated by performing analysis of variance (ANOVA) (SAS Institute, Inc. 1985) procedure in a randomized complete-block design, with treatments analyzed as fixed effects and reps as random effects. In each analysis, if the ANOVA indicated significant differences (P 
0.05), the means were compared by calculating least significant differences (LSD).
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
|
Anthesis Stage
The NDF concentration of meadow bromegrass was the highest among the entries in 1996 (Table 1). A similar ranking was observed in 1997; however, the NDF concentration of meadow bromegrass was not significantly different compared to smooth bromegrass and S-9073. The highest ADF concentration in 1996 was observed in meadow bromegrass, while the lowest concentrations were observed in smooth bromegrass and S-9183. The ADF concentration differences among the cultivars and populations were not significant in 1997. In both years, the CP concentration of meadow bromegrass was significantly lower than smooth bromegrass; however, there was no consistent ranking among the hybrid bromegrass populations.
Stem Nutritive Value
Vegetative Stage
The highest NDF concentrations were observed in the two parental cultivars and the hybrid bromegrass population S-9197 in 1997 (Table 2), with S-9073 and S-9183 being significantly lower. For ADF, S-9183 was significantly lower than all other lines, while meadow bromegrass was higher than all entries except S-9197. Meadow bromegrass was significantly lower in CP concentration than all populations except S-9197. The hybrids did not differ significantly among each other, but S-9197 and S-9073 were lower in CP than smooth bromegrass.
|
Anthesis Stage
The NDF concentrations among the parental cultivars and the hybrid bromegrass populations were not significantly different in 1996 (Table 2), despite a wide range of values. In 1997, smooth bromegrass and S-9183 had the highest NDF concentrations. The NDF concentration differences among meadow bromegrass and the other two hybrid bromegrass populations were not significantly different. Over both years, there were no significant ADF concentration differences among the parental cultivars and the hybrid bromegrass populations. There were no significant CP concentration differences among the entries in 1996; however, in 1997 the CP concentration of meadow bromegrass was significantly higher than the rest of the entries. The lowest CP concentrations were observed in S-9197 and S-9073.
Whole-Plant Nutritive Value
Vegetative Stage
In both years, the NDF and ADF concentrations of meadow bromegrass and smooth bromegrass were significantly higher than the three hybrid bromegrass populations (Table 3). Among the hybrid bromegrass populations, in 1996, the lowest NDF and ADF concentrations were observed in S-9183 hybrid bromegrass population. In 1997, the NDF and ADF concentration differences among the three hybrid populations were not significant. The CP concentration differences were not significant among the entries in 1996. In 1997, the highest CP concentration was observed in smooth bromegrass, while the differences among meadow bromegrass and the hybrid bromegrass populations were not significant.
|
Anthesis Stage
The NDF concentration of smooth bromegrass and S-9183 hybrid bromegrass was significantly higher than meadow bromegrass and the other hybrid bromegrasses in 1996 (Table 3). The NDF concentrations among the entries in 1997 were not significantly different. The ADF concentration of smooth bromegrass and S-9183 was significantly higher than meadow bromegrass and S-9073 in 1996. The ADF concentrations among the entries in 1997 were not significantly different. There were no significant differences in CP concentration between smooth, meadow and S-9183, and all these were higher than S-9073 and S-9197 in 1996. In 1997, S-9197 and S-9073 were again lower than meadow and smooth bromegrass in CP concentration, but not different than S-9183.
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
There are inherent morphological differences among the leaves of meadow, smooth, and hybrid bromegrass populations. Leaves of meadow bromegrass are pubescent, narrower, and longer than smooth bromegrass leaves. The leaf shape and size of the hybrid bromegrass populations resemble smooth bromegrass; however, there is pubescence on the hybrid leaf surface (Ferdinandez and Coulman, 2000). In previous studies, high and low digestible dry matter smooth bromegrass lines were linked to different leaf morphological characteristics. High in vitro digestible dry matter smooth bromegrass genotypes had leaves which were thick and long, and had large leaf area, leaf volume and specific leaf weight (Ehlke and Casler, 1985; Casler and Carpenter, 1989). Leaf anatomical characteristics are also known to differ between high and low IVDMD clones of smooth bromegrass (Ehlke and Casler, 1985). These high IVDMD clones, which were low in NDF and ADF concentrations, had significantly greater percentages of readily digestible tissue types (leaf mesophyll), and a significantly lower percentage of lignified leaf vascular tissue than low IVDMD clones. Even though detailed anatomical studies were not conducted in the present study, visual observations indicated that meadow bromegrass leaves contained thicker more prominent veins than smooth bromegrass and the hybrid bromegrasses.
In the present study, there was no consistent ranking among the parental cultivars and hybrid bromegrass lines for leaf blade fiber concentrations in the 2 yr. However, meadow bromegrass, which has longer leaves and the highest specific leaf weight (Van Esbroeck et al., 1995), often had higher leaf blade fiber concentrations than hybrid bromegrass. This may be due to more venation in the former resulting in a higher leaf blade lignin concentration. The lower leaf blade fiber concentrations of hybrid bromegrass lines compared with meadow bromegrass may be due to the leaf blades of the former more closely resembling those of smooth bromegrass.
Changes in the NDF concentration of smooth bromegrass stems have previously been associated with anatomical characteristics. According to Ehlke and Casler (1985) thicker smooth bromegrass stems are higher in in vitro digestibility becaue of smaller vascular bundles. Larger stems may be more digestible becaue of a dilution of the lignified tissue (Van Soest, 1994). On the contrary, in an earlier study conducted by Christie and Mowat (1968), no differences were detected for digestibility between coarse and fine stemmed clones of smooth bromegrass. Since there were no stem anatomical studies conducted in the present study, it is difficult to explain the often lower NDF values associated with the hybrid populations at early stages of development. It is possible that the stem of the hybrid populations has unique anatomical characteristics which resulted in lower NDF values than the parental species. It should be noted, however, that low stem fiber concentrations of hybrid bromegrass lines did not persist at later stages of development. This perhaps indicates a rapid lignification of the hybrid bromegrass populations at later stages of maturity.
The whole plant NDF and ADF concentrations of the hybrids were lower than those of parental species at the vegetative stage. Furthermore, the CP concentration of the hybrid bromegrass lines were frequently lower than parental cultivars at several growth stages. Even though a consistent ranking was not observed in both years, there appears to be a relationship between the selection objectives used in the development of the hybrid populations, their genetic makeup, and the whole-plant nutritive value at the anthesis stage. Bromegrass hybrid S-9183, which has the smooth bromegrass cytoplasm (developed by backcrossing the hybrid to smooth bromegrass), and was selected towards smooth bromegrass with better regrowth, had whole-plant fiber concentration values which closely resembled smooth bromegrass at later stages of development. The fiber concentrations of the S-9197 and S-9073 bromegrass hybrids, both of which have meadow bromegrass cytoplasm, showed later growth stage whole-plant fiber concentrations closer to meadow bromegrass. In a previous study, the hybrid populations and meadow bromegrass were found to have fewer reproductive tillers than smooth bromegrass (Ferdinandez and Coulman, 2000). This may explain the similarity in nutritive value of the hybrid populations S-9197 and S-9073 to meadow bromegrass.
There was no significant difference in the CP concentration at the anthesis stage between meadow and smooth bromegrass. Lack of significant difference in whole-plant CP concentration at this stage may be due to the leaf fraction of smooth bromegrass having a higher CP concentration than meadow bromegrass and the stem fraction of meadow bromegrass having a higher CP concentration than smooth bromegrass. It should be noted that the CP concentrations of the hybrid bromegrass populations at anthesis were often lower than the parental CP concentrations.
According to Van Soest et al. (1991), NDF is the best single plant predictor for potential forage intake, and ADF is an indicator of forage digestibility in ruminants. Reduction in both NDF and ADF concentrations would be desirable in the improvement of forage grasses. However, a concern in breeding for lower NDF concentrations in smooth bromegrass has been the associated reduction in forage grass yield (Falkner and Casler, 1998). The yield studies that have been conducted on the hybrids have indicated a comparable yield potential to the parents (Ferdinandez and Coulman, 2000). In hay management, the hybrids out-yielded meadow bromegrass, and in pasture clipping, the hybrids yielded more than smooth bromegrass (Coulman and Knowles, 1995). This suggests that the hybrids have the potential to be high quality forage grasses at early stages of maturity, but still obtain yields comparable to the standard types.
Lower fiber concentrations in the hybrid populations at the vegetative stage suggest that they may have higher nutritive value when grazed or cut early for hay at this stages of development. Of the three hybrids, S-9183 appears to have the best potential nutritive value for early utilization. For forage use at more mature stages, S-9073 and S-9197 were similar to meadow bromegrass, and lower than smooth bromegrass, in fiber concentration. In view of the small increases in the fiber concentration in meadow bromegrass at more mature stages, and its superior in vitro digestibility at these stages, Knowles et al. (1993) suggested that meadow bromegrass would be superior to smooth bromegrass for stockpiled forage. S-9073 and S-9197 hybrid bromegrass may share these characteristics. S-9183 was inconsistent in its ranking for fiber concentration at anthesis, so it is difficult to draw conclusions on the use of this hybrid population for stockpiling purposes.
|
ACKNOWLEDGMENTS |
|---|
Received for publication April 10, 2000.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  J. F. Karn, J. D. Berdahl, and A. B. Frank Nutritive Quality of Four Perennial Grasses as Affected by Species, Cultivar, Maturity, and Plant Tissue Agron. J., October 3, 2006; 98(6): 1400 - 1409. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Agronomy Journal | Vadose Zone Journal | |||
| Journal of Natural Resources and Life Sciences Education |
Soil Science Society of America Journal | ||||
| Journal of Plant Registrations | Journal of Environmental Quality |
The Plant Genome | |||
