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a Dep. of Environmental Sciences and Dep. of Plant Science, Nova Scotia Agricultural College, P.O. Box 550, Truro, NS, Canada B2N 5E3
b Dep. of Plant Sciences, Crop and Weed Ecology, Wageningen Agricultural Univ., Wageningen, The Netherlands
c Dep. of Horticulture, Virginia Polytechnical Inst. and State Univ., 201 Saunders Hall, Blacksburg, VA 24061
* Corresponding author (dcattani{at}nsac.ns.ca)
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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25 d after transplanting (DAT)], with anthesis by 35 DAT. Tiller initiation was earlier for PAL11 and UM67-10 compared with Emerald. Internode elongation was at least 4 d earlier for CB than for AB. Emerald and UM67-10 usually elongated above the third node on the main stem compared with the sixth node for PAL11. At 35 DAT, UM67-10 had reached the greatest leaf stage. PAE11 was highest on the West scale. West scale limitations resulted from lack of reproductive initiation by CB and PAL11. PAL11 had significantly higher root and shoot dry weights, root:shoot ratio, and more adventitious root growth than CB. Earlier internode elongation in CB may have diverted carbohydrates from root and leaf production. Internode lengths were greatest for Emerald, then UM67-10, followed by PAL11. Blade length was least for UM67-10. Sheath length increased with successive leaves. PAL11 had a quicker leaf appearance rate at earlier growth stages than CB. Delayed internode elongation in AB may provide an advantage in establishment from seed in an existing stand.
Abbreviations: AB, annual bluegrass • CB, creeping bentgrass • DAT, days after transplanting
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Annual bluegrass is the primary invasive species in cool season turfgrass worldwide (Beard et al., 1978; Kamp, 1981; Peel, 1982; Lush, 1989). Its competition with CB on golf greens is of a particular concern (Beard et al., 1978). Due to the presence of diverse biotypes, ranging from annual through perennial life cycles and between bunched and creeping growth habits (Peel, 1982), AB is very difficult to control under the management practices standardized for bentgrass-based golf greens. Lush (1989) found that AB biotypes from golf greens had more leaves on the main stem prior to the emergence of inflorescence than biotypes found in fairways or roughs (Lush, 1989). Knowledge of plant growth and developmental patterns are key elements towards understanding interplant and interspecies competition and to the development of new turf management practices and cultivars.
Several scales for quantifying plant growth and developmental stages have been proposed and utilized across the past three decades (Haun 1973; Klepper et al., 1982; West, 1990; Moore et al., 1991). Most of these scales, directly or indirectly, rely on the phyllochron. "The phyllochron or number of GDD (growing degree days) between a leaf number of n and n + 1 results from a combination of genetic and environmental factors that interact to produce leaves in an orderly and predictable manner" (Frank and Bauer, 1995). These scales are used to quantify crop growth in an effort to report yield and developmental data in terms other than time. Air temperature is the primary factor regulating the phyllochron or leaf succession (Klepper et al., 1982). Haun (1973) scale is based on successive leaf appearances, while West (1990) scale, designed for stoloniferous grasses, is based on leaf appearance for early growth, followed by tiller elongation characteristics, and lastly, on different stages of reproductive growth.
Using both the Haun and West scales, we intend to better understand plant development, and how this may impact competition within and between these two species. A previous study with CB demonstrated significant differences in tiller development (Cattani, 1999) and dry matter partitioning between aboveground tiller branches between germplasms (Cattani and Struik, 2001). The potential for new tiller initiation is linked to leaf development (Neuteboom and Lantinga, 1989), and thus depends on the appearance rate of leaves. Understanding the inherent differences between germplasms and species for phyllochron may be used to explain tiller number differences on the basis growth stage attained.
The objectives of this study were to compare (i) plant growth and development and (ii) leaf and internode growth and development, in two divergent flowering biotypes of AB and two divergent tillering types of CB.
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MATERIALS AND METHODS |
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Daily measurements were made with respect to leaf number and internode development through 35 DAT. The Haun growth stage (Haun, 1973) was used only to measure leaf number on the main stem, and the West growth stage (West, 1990) was used to measure first tiller appearance, internode elongation, and reproductive development of the main stem. The starting point for the Haun stage was the appearance of the tip of the second leaf. The Haun scale assigns a growth stage based upon the relative length of the youngest collared leaf to the next appearing leaf. The West scale assigns values based upon specific events. Values 4 to 9 are for the appearance of the first through the sixth leaf. The appearance of the first tiller is assigned the value of 10. The appearance of an elongating internode is assigned an 11, with each successive internode up to the ninth receiving a value of 12 to 19. Values 20 to 29 are for seedhead emergence, with 30 to 39 assigned to stages of flowering.
Emerald in the first run of the experiment was very slow to reestablish and was therefore removed from the analysis. A severe limitation to the West scale is the ability of CB to produce more than nine internodes without reproductive initiation, thus reaching the limit on the scale. Measurements of leaf length, leaf width, sheath length, and internode length were made prior to 35 DAT. At 35 DAT, some CB plants had produced more than nine internodes, thus exceeding the limit of the West scale for that characteristic. Therefore, internode number was used to describe CB stem development. Tillers per plant were counted at Days 14, 21, 28, and 35 DAT in the first run, and 14, 21, and 28 DAT in the second run (due to the high number of tillers, the 35-DAT count was not conducted). The node at which stem elongation occurred first was recorded, and total stem length, from that node to a distal end of the last fully elongated internode, was measured at 35 DAT. Root washing was performed and the plants were separated into root, main stem (all material above the node where stem elongation was initiated), and the remaining shoot material. Dry weight was determined after the plant materials were dried at 65°C for 72 h in a forced air oven.
Data Analysis
Analysis of variance was performed for each run of the experiment with PROC ANOVA in SAS (SAS Institute, Cary, NC) with the exception of leaves on the main stem, where PROC GLM was used due to damage of the main stem on one plant. The analysis was carried out on an individual run basis due to the difference in the number of germplasms, with PAE11 being determinant in growth habit, and we were primarily interested in the comparison between germplasms. Mean comparisons were made using Dunnett's t-test. Data were analyzed at on a germplasm basis across runs to identify leaf and internode characteristics of the individual germplasms.
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RESULTS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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In both runs, the first tiller appearance was recorded significantly earlier in PAL11 than in PAE11 (Table 2). UM67-10 was statistically similar to PAE11 in Run 1 and to PAL11 in Run 2, and Emerald was similar to PAE11 in Run 2 (Table 2).
Internode appearance date was significantly earlier for CB than AB entries in both runs. Internode elongation occurred first in UM67-10 in Run 1 and both CB entries in Run 2, >3 d earlier than in the AB germplasms (Table 2).
The number of nodes below the node of elongation was significantly lower for the CB than AB in both runs (Table 2). UM67-10 
PAE11 PAL11 in both runs, with Emerald being significantly less than UM67-10 in Run 2 (Table 2).
Compared with AB, CB had a significantly higher number of elongated internodes on the main stem (Table 2). PAE11 had significantly lower values than PAL11 in Run 2, but were similar in Run 1, indicative of the greater leaf number attained in Run 2 by PAL11 (Table 2).
Main stem length at 35 DAT was also significantly higher for CB than AB in both runs (Table 2). UM67-10 PAE11 PAL11 in Run 1, while in Run 2 Emerald = UM67-10 
PAE11 = PAL11 (Table 2).
Tiller Development
Linear regression was performed for logn of tiller number on leaf stage across both runs of the study (Fig. 1)
. All data fitted linear regression models (on transformed data) with high R2 values ranging from 0.942 to 0.983 (Fig. 1). Final tiller number was highest for PAL11 and UM67-10 (Fig. 1a, c). Slope values indicate the overall tiller bud conversion to tillers relative to leaf number on the main stem attained. Emerald had the highest slope value at 0.618, followed by PAL11 and UM67-10 with slope values of 0.472 and 0.449, respectively (Fig. 1a, c). PAE11, due to its determinant leaf number on the main stem, produced a slope of 0.721 (data not shown).
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Main stem dry weight was not significantly different between germplasms in Run 1 (Table 3). Emerald was significantly than PAL11, which was than PAE11 and UM67-10 (Table 3). The higher main stem dry weights in Run 2 again reflect the greater physiological age achieved in Run 2 (Tables 2 and 3).
Total plant dry weight data rank PAL11 as the highest biomass accumulator, compared with the other germplasms (Table 3). PAE11 was significantly higher than UM67-10 in Run 1; however, they were similar in Run 2 (Table 3).
Emerald was similar to UM67-10 for all dry weight measurements in Run 2, with the exception of having a significantly higher main stem dry weight (Table 3).
PAL11 also had the significantly highest root:shoot dry weight ratio for both runs. The remaining germplasms were statistically similar within runs (Table 3).
Growth Scales
PAE11 demonstrated a determinate growth habit, producing a seedhead after seven or eight leaves on the main stem. Plants with these growth habits will be referred to as PAE11-7 or PAE11-8, respectively.
A comparison of Haun and West scales for the germplasms exhibiting indeterminate growth in this experiment indicate two differences (Fig. 2) . First, the West scale started to deviate from the Haun's scale at the initiation of tillering. The West scale remained static until the initiation of internode elongation, and paralleled the Haun scale response values until Internode 9, where attained. The West scale will then remain unchanged until reproductive tillering is apparent. PAL11 produced the first tiller in Runs 1 and 2, earlier or similar to CB; however, internode elongation was significantly later, at 26.6 and 20.6 DAT for PAL11 in Runs 1 and 2, respectively (Table 2), and proceeded at a slower rate (Fig. 2).
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Leaf Characteristics
Phyllochron
Phyllochron, in general, shortened with successive leaves, until the eighth leaf, then leveled off for CB (Table 4). Annual bluegrass demonstrated a quicker decline at earlier stages with an increase at the sixth to seventh leaf stage (Table 4). PAL11 demonstrated a quicker decline in phyllochron than CB; however, there was an increase for the phyllochron between leaf 6 and 7 (Table 4).
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11 cm for PAL11 (Fig. 4a)
. In CB, leaf length leveled off at approximately the seventh leaf stage, at 6 cm and 10 cm for UM67-10 and Emerald, respectively (Fig. 4b). PAE11-7 and PAE11-8 increased in length until the seventh leaf, where there was a significant decrease for PAE11-7, the flag leaf (Fig. 4a). PAE11-8 had a significant blade length decrease for the eighth leaf (flag leaf) (Fig. 4a).
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Internode Length
Across the 35 DAT, the mean internode length gradually increased for UM67-10 and Emerald, up to 4.5 cm (10th internode) and 6.5 cm (eighth internode), respectively (Fig. 6)
. Emerald and UM67-10 both initiated internode elongation at the third internode. In PAL11, the initiation of internode elongation appeared later in development (sixth internode) and the initiated internodes had a slower increase in length, to a mean length of 1.3 cm at the ninth internode (Fig. 6). Internode appearance dates can be extrapolated on Fig. 2 on the West scale.
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DISCUSSION |
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Dry matter partitioning in AB germplasm demonstrated higher allocation of biomass to roots (Table 3). Because of the initiation of reproductive growth, PAE11 was similar to CB for root:shoot partitioning. Similar tiller initiation times coupled with later internode elongation, both with respect to chronological time and leaf stage (Table 2), likely allow for greater carbohydrate availability for rooting at the early growth stages in AB. Although CB is noted for rapid root initiation into nutrient rich environments (Crick and Grime, 1987), AB in the present study produced at least equal root mass to CB (Table 3) and had greater number of adventitious roots (visual assessment) at the growth stages reached in the present study.
Ross and Harper (1972) defined occupation of biological space as "a plant gaining access to resources for its further growth and development." Bernston and Wayne (2000) reported that while belowground competition is linearly related to the size of the root system, aboveground competition was asymmetric with respect to light capture, with plant height and leaf area being important factors. Therefore, the growth demonstrated by AB indicates that it appears to have a competitive advantage both above and below the ground.
The differences in dry weight observed between the two runs were much larger than expected (Table 3). Tiller number can theoretically double with each new leaf on the main stem after the third leaf (Neuteboom and Lantinga, 1989), therefore, dry weight increases under noncompetitive conditions should be exponential in nature during the exponential growth phase. Earlier appearance of the first tiller by more than 1 d in Run 2 also provided the plants with greater photosynthetic opportunity, which likely led to the dry weight increases seen.
Emerald and UM67-10 had similar biomass (Table 3), confirming results from an earlier study (Cattani, 1999). UM67-10 had more elongated, yet shorter internodes than Emerald (Table 2, Fig. 6), and this may have lead to the similar total biomass values. Plant developmental status is most likely the reason for the loss of significance of PAE11 over UM67-10 for many of the dry weight traits as PAE11 had become reproductive and therefore, sink demands should have changed (Table 3).
Variations in leaf and internode characteristics were greater between and within CB germplasms than in AB, most likely due to its outcrossing nature (Bradshaw, 1958). The relative uniformity of leaf, sheath, and internode lengths within PAE11-7 and PAL11 indicate that these may be considered as true-breeding lines. The greater variation within PAE11-8 indicates that it may still be segregating. Hunt et al. (1987) reported that both CB and AB prefer environments that are physically disturbed. Annual bluegrass generally competes via new plant establishment (Lush, 1989), while CB spreads via vegetative growth (Jonsdottir, 1991; Bullock et al., 1994). Our data indicates that CB seedlings invest earlier in stem development, in an attempt to colonize the surrounding area, as demonstrated by the earlier onset (temporal and developmental) of internode elongation.
A longer phyllochron during early growth, primarily at the third to fourth leaf stage, may reduce CB's ability to establish in existing stands (Jonsdottir, 1991; Bullock et al., 1994; Sweeney and Danneberger, 1998). The third internode is usually the first to elongate, possibly drawing nutrients away from leaf production and new tiller initiation, as found in white clover (Trifolium repens L.) (Chapman and Robson, 1992). Seedling competitiveness is important for plant establishment, and if CB seedlings are less competitive, AB will colonize the opening. Cattani and Nowak (2000) reported that competition from live turf reduced the plant growth in both CB and AB, although AB was able to achieve greater growth stages.
Another factor which may affect early phyllochron development is leaf vernation or emergence type. Annual bluegrass leaves emerge from the previous leaf in a folded fashion while CB leaves emerge rolled (Hitchcock, 1935). Annual bluegrass leaf tips have exposure to light prior to the collar appearance on the previous leaf. Conversely, CB leaf tips are shrouded until collar emergence. Creeping bentgrass leaves are tapered with the basal end being wider than the distal end, and AB leaf margins are parallel for the majority of the leaf blade length. The wider base, coupled with the rolled emergence keeps the leaf blade rolled until the collar is free of the previous leaf, effectively shading the next leaf.
Early leaf blade length increases were more gradual for AB than CB. Creeping bentgrass leaf tips did not appear until the previous leaf was fully emerged and fully exposed to light. Leaf blade length increase between Leaves 3 and 4 were >50% in CB and <30% in AB (Fig. 4). Martre et al. (2000) suggest that active transpiration of the leaf tip may limit the growth rate of the leaf. Given the greater rates of leaf length increases in CB at early stages of growth, this may lead to longer phyllochrons, as seen in the present study. The observed relative leaf blade length increase differences may give the competitive advantage of AB. Reduced leaf length in CB appears to influence plant tiller number (Cattani, 1999) and internode length. These characteristics should determine the choice of cultivar for specific uses. Greater environmental disturbance (e.g., divots from golf course fairways) would favor plants with longer internodes to effectively colonize damaged areas, while plants with high tiller number would create high tiller densities desired for golf greens.
Seed size of the species may also determine the rate of early seedling growth. CB has an average seed weight of 0.07 mg (Turgeon, 1999), compared with 0.55 mg for AB (Lush, 1989). Larger seed size, coupled with similar blade lengths for Leaves 1 and 2 may give AB a nutritional advantage until photosynthesis and roots take over the supply of carbohydrates and minerals. Long-term implications with respect to turf management and control of AB within CB stands depend on the AB genotypes. Unpublished research by D. Cattani indicates that the biotypes of AB present on golf greens from Atlantic Canada vary from course to course and between greens on the same course. Management practices, such as mowing height, soil type, green's topography, irrigation, and fertility may influence this diversity. Similar AB control practices used on different courses may preferentially allow establishment of certain biotypes.
Annual bluegrass has been and will continue to be an invasive species in highly managed turf (Beard et al., 1978). Its ability to sexually reproduce under golf green management conditions creates a seed bank that is difficult to control (Lush, 1989). Annual bluegrass also appears to have a competitive advantage over CB due to its leaf morphology and development patterns. Variation between germplasms for both AB and CB however, indicates that inter- and intraspecies competition is not easily defined without specific knowledge of the plant materials present. Therefore, management recommendations should rely on detailed information of the plant biotypes present.
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Received for publication February 6, 2001.
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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  J. FUSTEC, J. GUILLEUX, J. LE CORFF, and J.-P. MAITRE Comparison of Early Development of Three Grasses: Lolium perenne, Agrostis stolonifera and Poa pratensis Ann. Bot., August 1, 2005; 96(2): 269 - 278. [Abstract] [Full Text] [PDF]
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