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CROP ECOLOGY, PRODUCTION & MANAGEMENT

Differences in Tillering of Long- and Short-Leaved Perennial Ryegrass Genetic Lines under Full Light and Shade Treatments

^a Institut National de Recherche Agronomique, Unité d'Ecophysiologie des Plantes Fourragères, F-86600 Lusignan, France, and Dairying Research Corp., Private Bag 3123, Hamilton, New Zealand
^b Institut National de Recherche Agronomique, Unité de Génétique et d'Amélioration des Plantes Fourragères, F-86600 Lusignan, France
^c Institut National de Recherche Agronomique, Unité d'Ecophysiologie des Plantes Fourragères, F-86600 Lusignan, France
^d Institut National de Recherche Agronomique, Unité de Génétique et d'Amélioration des Plantes Fourragères, F-86600 Lusignan, France
^e Institut National de Recherche Agronomique, Unité d'Ecophysiologie des Plantes Fourragères, F-86600 Lusignan, France
^f Institute of Natural Resources, Massey Univ., Private Bag 11-222, Palmerston North, New Zealand
^g Dairying Research Corp., Private Bag 3123, Hamilton, New Zealand

bahmanii{at}drc.co.nz

	ABSTRACT

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusion REFERENCES

 
There is uncertainty among plant breeders as to which characteristics to select for to optimize grass growth dynamics. The objective was to study the relationship between leaf length and tillering in perennial ryegrass (Lolium perenne L.). Two long-leaved and two short-leaved genetic lines were grown in simulated shade and near-full sunlight (control) environments. The genetic lines were New Zealand cultivars Ellett (long-leaved) and Grasslands Ruanui (short-leaved), both early flowering. The other two were late-flowering divergent selections `LL' (long-leaved) and `SL' (short-leaved). Differences between genetic lines in leaf length were attributable mainly to higher leaf elongation rate (LER) in the two long-leaved genetic lines, and leaf elongation duration (LED) did not differ significantly between genetic lines. Grasslands Ruanui had a higher tiller number per plant than Ellett in both light environments, explained by higher site filling but similar leaf appearance rate (A_L). In contrast, LL had a higher tiller number per plant than SL, arising from a higher A_L in LL. This difference decreased during the experiment under the control treatment because SL tended to have a higher site filling ratio than LL. However, in the shade treatment, differences in tiller number between LL and SL were more mediated by A_L than site filling. Therefore, selection for high LER and long lamina length, even though associated with reduced site filling in all treatments, did not necessarily result in reduced tiller number per plant.

Abbreviations: A_L, leaf appearance rate on the main shoot • A_T, tiller appearance rate on the main shoot • GDD, growing degree-days • LAI, leaf area index • LED, leaf elongation duration • LER, leaf elongation rate • PAR, photosynthetically active radiation • F_S, site filling • F_Sm, site filling calculated from observations on the main shoot • SU_m, site usage on the main shoot • LL, long-leaved breeding line obtained by divergent selection out of a collection of French ecotypes • SL, short-leaved breeding line obtained by divergent selection out of a collection of French ecotypes

	INTRODUCTION

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusion REFERENCES

 
LEAF ELONGATION RATE, leaf appearance rate (A_L), leaf elongation duration (LED), final leaf length, and tiller appearance rate (A_T) are interdependent in their control of forage and turf grass growth (Fig. 1) . In particular, A_L controls both numbers of tiller buds produced and LED. As A_L decreases, LED increases (Robson, 1967) and the number of tiller buds produced decreases, since there is one tiller bud in the axil of each leaf. Consequently, a low A_L could result in the production of a low number of large tillers (Lemaire and Chapman, 1996). However, tiller appearance also depends on the propensity for tiller buds to develop into tillers. The earliest measure of tiller bud activity was site filling (F_S) ratio (Davies, 1974), defined as the ratio of tiller production to leaf production, or equivalently the natural logarithm of the factor by which tiller number per plant increases with each leaf appearance interval. Site filling has a theoretical maximum of 0.69 (Log_n2), denoting doubling of tiller population with each leaf appearance interval (Neuteboom and Lantinga, 1989). More recently tillering activity has been measured as site usage (Skinner and Nelson, 1992), or nodal probability (Matthew et al., 1998); effectively the proportion of tiller buds that eventually form new tillers, with a theoretical maximum of 1.00. There is presently limited understanding at the physiological level of the inter-relationships shown in Fig. 1 and of their interaction with environmental factors such as light and temperature. Consequently there is uncertainty among plant breeders as to which characteristics to select for to optimize plant performance.

View larger version (20K): [in this window] [in a new window]   Fig. 1 Relationship between leaf growth components, sward LAI, and tillering. Variables in bold type were measured in this experiment

Light environment can also modify leaf growth and tiller appearance. Self-shading within a dense canopy at the tiller base is associated with an increase of leaf length and a decrease of tillering (Kays and Harper, 1974). Casal et al. (1985, 1987) linked these effects with low red/far red ratio associated with shading, which triggers an increase in leaf area, through increased LER and LED (Allard et al., 1991), resulting in compensation for the lower light interception. Consequently, the effect of high sward leaf area index (LAI) in inhibiting tillering (Simon and Lemaire, 1987) is an important mechanism in the negative correlation between tiller density, and leaf length which in turn is a major component of sward LAI.

Finally, breeding for high yield through selection or chromosome doubling has led to a tendency, in modern perennial ryegrass genetic lines, towards swards having a lower density of larger tillers (see e.g., Hunt and Easton, 1989; Van Loo, 1992; Bahmani et al., 1997). Concerns have been expressed by farmers and researchers about the poor persistence of these modern ryegrasses in pastures (Thom et al., 1998). Persistency of perennial ryegrass depends on the equilibrium between the relative rate of tiller initiation and tiller death (Langer, 1963). Breeding for increasing tiller size may therefore have restricted tillering ability of the selected genetic lines.

To study the relationships outlined above, morphogenetic characteristics of two commercial cultivars and two experimental breeding lines of perennial ryegrass with contrasting leaf length characteristics and maturity dates were studied under two contrasting light environments, near-full sunlight and simulated shade.

	Materials and methods

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusion REFERENCES

 
Plant Material
The two commercial cultivars used were Ellett (long-leaved) and Grasslands Ruanui (short-leaved), originating from New Zealand, and both early flowering (Corkill et al., 1981). Grasslands Ruanui was first released in 1936 and Ellett in 1975. In a dense sward, in normal farm practice, Ellett has a lower tiller density and larger tiller size than Grasslands Ruanui (Easton, 1983; Bahmani et al., 1997). The two experimental breeding lines were derived from divergent selection for leaf length from a collection of French ecotypes (Hazard et al., 1996). For simplicity, when referring collectively to the two commercial cultivars or the two experimental breeding lines in the text below, the term genetic lines will be used. Although the experiment comprised two early- and two late-flowering genetic lines, all plants remained vegetative for the duration of the experiment. All plant material was endophyte free.

Experimental Site, Design, and Conditions
The experiment was carried out at INRA, Lusignan, France (Latitude, 46°26' N, Longitude, 0°09' E) from February to May 1998. Seed of the four ryegrass genetic lines were germinated in Petri dishes on 2 Feb. 1998, then transplanted (9 March 1998) into pots (170-mm diam, one plant per pot) containing a mixture of sterilized soil, sand, and peat (1:1:1). The plants remained in a glasshouse from 9 March to 8 April 1998, when 80 plants of each genetic line were arranged in eight trays of 40 plants. Two trays containing 40 Ellett and 40 Grasslands Ruanui plants, and two trays containing 40 LL and 40 SL plants, in each of two methyl methacrylate filters. These 320 individually potted plants are the experimental units on which statistical analyses described below are based. Because Ellett and Grasslands Ruanui plants and LL and SL plants were randomized in equal numbers in alternate trays, results for the respective pairs of genetic lines were analyzed as separate experiments. The light environments were not replicated, and this raises issues in interpretation of results that are discussed further below. Trays were 0.85 m wide and 1.4 m long and were raised 0.7 m above the ground under larger canopies, also raised above the ground. This construction prevented direct sunlight reaching the plants, but allowed free air circulation for temperature stabilization.

The canopy used as the control light treatment transmitted 90% of photosynthetically active radiation (PAR), without spectral modification. The filter used to simulate a green shade (i.e. the shade treatment) transmitted 15% of PAR, but only 6% of blue and with a reduced red/far red ratio of 0.17. When the light treatments were commenced on 8 April 1998, the main shoot had four fully emerged leaves, on average. Degree-day values cited in this paper are calculated commencing from this date.

The plants were watered individually every 2 h with an automatic irrigation system. Air temperatures inside each canopy were continuously recorded throughout the experiment (10-s sampling interval and 5-min recording interval) with thermocouples located 30 mm above the soil surface. Differences in daily temperature between the two light environments averaged 0.4°C. Air humidity was monitored from 12 to 17 May 1998 with a psychrometer located 150 mm above the soil surface (sampling and recording intervals as for air temperature). Differences in air humidity between the control and shade treatments were small (<3%) and inconsistent.

Measurements
The number of mature and emerging leaves and primary tillers present on the main shoot, and the number of tillers per plant were counted three times a week, from 8 April to 11 May 1998. New tillers were recorded when the leaf tip appeared above the subtending leaf sheath. The length and width of each fully emerged leaf on the main shoot were measured from Leaf Number 4 to Leaf 8.

Derived Data
A_L, A_T, and LER were determined for the main shoot. A_L and A_T were calculated as the slope of the regression of number of fully developed leaves or tillers on thermal time (calculated from 8 April, base temperature 0°C). The temperature summation in degree-days was calculated from daily mean temperature measured under each canopy. LED was measured from main shoot Leaf Number 5 to Leaf 8 as the number of degree-days between the leaf appearance and full emergence. LER was then estimated by dividing final leaf length by LED. The average leaf length, LED and LER were calculated for each genetic line in each light environment from the mean for Leaves 6 to 8 appearing during the measurement period. Site filling (Fs) was calculated as the slope of the linear regression between the logarithm of the number of tillers per plant and the number of leaves appeared on the main shoot, since no mortality occurred during the measurement period. This relationship follows from Davies' (1974) definition of site filling mentioned above, and is illustrated graphically in Fig. 4a and 4b .

View larger version (28K): [in this window] [in a new window]   Fig. 4 Effect of light treatments on site filling (FS) of (a) early-flowering and (b) late-flowering ryegrass genetic lines. Slope coefficients of equations are values of FS. Shade effects were significant at P < 0.001 in all cases; E, Ellett; R, Grasslands Ruanui; LL, long-leaved selection; SL, short-leaved selection; C, control light environment; S, simulated shade environment

(1a)

Which allowing that SU_m is equivalent to A_T/A_L, can be rearranged to:

(1b)

Since values for the delay between leaf and tiller appearance were close to 1.0 (see results, below), Eq. [1b] was adopted.

Analyses of variance were performed by PROC GLM of SAS (SAS Institute Inc., Cary, NC) to study the effects of light environment, genetic line and the interactions between genetic line, light environment effects and growing degree-days (GDD) on tiller number per plant, and tiller and leaf appearance rates, site filling, leaf length, leaf elongation and duration rates before and after 148 GDD. Separate analyses were carried out for the two early and the two late-flowering genetic lines.

	Results

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Main Shoot Leaf Length, LER, and LED
No significant interaction was found between genetic line and light environment for leaf length, LER, and LED for either early- or late-flowering genetic lines. The shade treatment increased leaf length by 55% compared with the control treatment (P < 0.001, Table 1) . This increase resulted from an average 35% increase in LER in all genetic lines, (P < 0.001), and for Ellett and Grasslands Ruanui from a 30% increase in LED compared with the control treatment (P < 0.001). The LED of the late flowering selections was unchanged by light treatments (Table 1).

View larger version (38K): [in this window] [in a new window]   Fig. 2 Leaf and tiller appearance on the main shoot for (a) early-flowering and (b) late-flowering genetic lines. Analysis of variance showed a significant difference for AL (P < 0.001) but not for AT (P > 0.01) in both light treatments between Ellett and Grasslands Ruanui, and between LL and SL; E, Ellett; R, Grasslands Ruanui; LL, long-leaved selection; SL, short-leaved selection; C, control light environment; S, simulated shade environment

View larger version (27K): [in this window] [in a new window]   Fig. 3 Effects of light treatments on tiller number per plant for (a) early-flowering, and (b) late-flowering genetic lines. In all cases, differences between shade and control treatment were highly significant (P < 0.001). Measurements were made to 350 GDD; E, Ellett; R, Grasslands Ruanui; LL, long-leaved selection; SL, short-leaved selection; C, control light environment; S, simulated shade environment

From extrapolation of the linear regression lines (Fig. 4a and 4b), the first tiller appeared when Grasslands Ruanui had 1.77 leaves on the main shoot, Ellett 1.84, LL 1.90 and SL 1.96 leaves.

Comparison of Main Tiller and Whole Plant Site Filling
Whole plant site filling, F_S, was only slightly less than main tiller site filling, F_Sm under the control treatment. By contrast, under the shade treatment, F_S was very much lower than F_Sm (Table 2).

	Discussion

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusion REFERENCES

 
Experimental Design
Nonreplication of the light environments raises issues in interpretation of the results. In such cases, the probabilities determined statistically for class mean differences are valid, but assigning those differences to the experimental treatments may or may not be, depending on whether or not confounding with external factors, such as shadows from nearby buildings, occurred. Independent of this consideration, where light environment is modified by housing, as in this experiment, the possibility of associated temperature and/or humidity differences must be considered. The latter problem was addressed in this work by housing both light environments with a canopy of identical design, by designing canopies for good ambient air circulation by convection to eliminate internal heating, and by continuous automatic monitoring of both relative humidity and temperature, the latter at multiple points within each light environment. The differences in temperature and humidity were never biologically significant. On the issue of possible confounding between light environment and external factors, it would have been impractical to house individually the experimental units, single potted plants, and the regression analyses used to relate leaf and tiller appearance would not have been easily adapted to handle a split-plot design. As a more realistic alternative, extreme care was taken in the siting of the full light and simulated shade canopies close to each other but not so close that one would shade the other, raised from the ground, and distant from trees, buildings, and other structures, to eliminate any such confounding. Plants of the two pairs of long- and short-leaved genetic lines were individually potted and fully randomized within canopies. There remains a very small chance that some external factor may have been overlooked and the results below are presented with that qualification. However, the overwhelming balance of probability is that the class mean differences observed were due to the differences in light environment.

Effect of Shade on Plant Development
Shade consistently increased final leaf length (Table 1) and reduced tiller appearance rate (Fig. 2 and 3). The differences in leaf length for Grasslands Ruanui and Ellett and for LL and SL have been described previously (see e.g., Easton, 1983; Hazard et al., 1996), are genetically determined, and were maintained in both light environments. Effect of shade on leaf length was mainly through increased LER, but also through increased LED in Ellett and Grasslands Ruanui. Effect on tiller appearance rate was through decreased F_S, but not F_Sm. The factor increase in tiller number per plant per leaf appearance interval can be calculated as e^Fs (Neuteboom and Lantinga, 1989). When applying this calculation to data in Table 2, shade reduced main shoot tiller appearance by 11%, compared with 31% for whole plant tiller appearance. It is therefore clear that formation of primary tillers on the main shoot is much less susceptible to shading than is formation of higher order secondary and tertiary tillers. This is consistent with previous studies in wheat (Triticum aestivum L.). For example, Casal (1988) also showed that the proportion of primary to secondary and tertiary tillers was larger in far-red treated wheat plants than in untreated plants. Bos and Neuteboom (1998b) measured SU at specific bud positions for wheat and also found differences in bud utilization between tillers at different hierarchical positions.

Shade treatments were imposed when plants had four leaves on the main tiller but changes in site filling were not evident for another 1.5 leaf appearance intervals (Fig. 4a and 4b). The extent of the delay in response to shading depends on the status of the tiller buds and the growth rate of daughter tillers within the sheath of the main tiller. The fact that recently initiated tiller buds were not recorded as daughter tillers until their leaf tip appeared above the subtending leaf sheath, was another factor contributing to this delay.

Relationship between Leaf Length and Tiller Appearance
Long leaf length has been associated in some previous studies with increased LED and low A_L (cf. Fig. 1), resulting in low tiller number per plant. Such responses have been previously observed in tall fescue (Robson, 1967; Zarrough et al., 1984; Allard et al., 1991) and wheat (Bos and Neuteboom, 1998a) and were identified as a general principle by Lemaire and Chapman (1996). However, in this experiment the selection LL had both high LER and high A_L, showing that these two variables need not always be negatively related. Indeed, Skinner and Simmons (1993) have already shown that supplemental far red illumination in grass seedlings increased leaf length through an increase in LER while LED was unaffected. The present result also suggests that the LL selection for high LER and leaf length have a different genetic basis than that of previous selections with a similar behavior.

Another mechanism that can give rise to negative association between LER and A_L is a negative relationship between LER and Fs. In our experiment, comparisons of Grasslands Ruanui with Ellett, SL with LL, and the control treatment with the shade treatment, all showed a common response in that high site filling was associated with low LER and short leaves. A similar observation was made by Zarrough et al. (1984) in tall fescue. Intuitively, a negative association between F_S and LER might be viewed as an indication of competition between daughter tiller and adjacent leaf meristems for available carbon, but the response could equally well be morphogenetically determined. Since a plant whose tillers have high LER will accumulate sward LAI more quickly after defoliation, the same plant will experience basal shading and shifts in light quality, and associated tiller bud suppression earlier in the regrowth cycle.

Factors Affecting Tiller Number per Plant
The delay between the appearance of a given leaf and the appearance of its axillary tiller (termed "n" by Neuteboom and Lantinga, 1989) can be measured for the main tiller as the vertical distance between regression lines of A_T and A_L on GDD (Fig. 2), since all tillers formed on the main tiller during the experiment were from the bud immediately above the previous tiller, with no buds missed. This delay was a little greater for LL than SL, did not differ between Grasslands Ruanui and Ellett, but did increase as plants aged (Fig. 2). Also of interest is the time of appearance of the first primary tiller. On the basis of extrapolation of regression lines in Fig. 4, the first tiller appeared sooner (1.77 leaves) in Grasslands Ruanui than in Ellett (1.84 leaves), but sooner in LL (1.90 leaves) than in SL (1.96 leaves). These apparent differences in timing of first primary tiller appearance may partly explain the high tiller number per plant in Grasslands Ruanui compared with Ellett, and the initially higher tiller number per plant in LL, compared with SL. Another factor contributing to the higher tiller number per plant in LL than in SL at the beginning of the experiment (18 degree-days) must have been the difference in A_L because LL had more leaves than SL at this time. At the end of the experiment, differences in tiller number per plant had diminished because of the higher site filling of SL, and could eventually exceed that of LL (Fig. 3b). Gautier et al. (1999) have also shown that long-leaved perennial ryegrass from the same population as LL had a lower tillering rate than comparable SL material, because of lower site filling.

Under the shade treatment, LL still produced more tiller bud sites than SL but, unlike the control treatment, both genetic lines had similar F_S. It is possible that increase in delay between leaf and tiller appearance, "n", which can include the inhibition or bud mortality of higher order tillers, explains lower site filling in simulated shade. However, since our observations were made only on main stem tillers, further investigations are necessary to accurately determine why F_S is much lower than F_Sm under the shade treatment.

	Conclusion

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusion REFERENCES

 
Increased leaf length of Ellett and LL genetic lines was achieved mainly through increased LER. This has been associated with increased productivity in both cases (Hunt and Easton, 1989; Hazard and Ghesquière, 1997), but contrary to previous indications (Robson, 1967; Zarrough et al., 1984), decreased A_L and tillering were not necessarily associated with long leaf length. This occurred with Ellett, but not with LL. This suggests it may be possible to select for higher tillering rate at a given tiller size, although other strategies to improve persistence, such as selection for increased longevity of individual tillers (Neuteboom et al., 1992) should also be kept in mind.Lonsdsale Watkinson 1982

	ACKNOWLEDGMENTS

 
We thank the Scientific and Cultural Service of the French Embassy in Wellington and the New Zealand Foundation for Research, Science and Technology for financial support. The assistance of Christophe De Berranger, Marie-françoise Pissard and Annie Eprinchard with experimental work was very much appreciated. New Zealand Agriseeds Ltd provided the Ellett ryegrass seed, and AgResearch Lincoln, New Zealand, the Grasslands Ruanui seed.

Received for publication August 3, 1999.

	REFERENCES

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusion REFERENCES

 

• Allard G., Nelson C.J., Pallardy S.G. Shade effects on growth of tall fescue: I. Leaf anatomy and dry matter partitioning. Crop Sci. 1991;31:163-167.[Abstract/Free Full Text]
• Bahmani I., Thom E.R., Matthew C. Effects of nitrogen and irrigation on productivity of different ryegrass ecotypes when grazed by dairy cows. Proc. N.Z. Grassl. Assn. 1997;59:117-123.
• Bos H.J., Neuteboom J.H. Growth of individual leaves of spring wheat (Triticum aestivum L.) as influenced by temperature and light intensity. Ann. Bot. (London) 1998;81:141-149 a.[Abstract/Free Full Text]
• Bos H.J., Neuteboom J.H. Morphological analysis of leaf and tiller number dynamics of wheat: Responses to temperature and light intensity. Ann. Bot. (London) 1998;81:131-139 b.[Abstract/Free Full Text]
• Casal J.J. Light quality effects on the appearance of tillers of different order in wheat (Triticum aestivum). Ann. Appl. Biol. 1988;112:167-173.[ISI]
• Casal J.J., Deregibus V.A., Sanchez R.A. Variations in tiller dynamics and morphology in Lolium multiflorum Lam. Vegetative and reproductive plants as affected by differences in red/far red irradiation. Ann. Bot. (London) 1985;56:553-559.[Abstract/Free Full Text]
• Casal J.J., Sanchez R.A., Deregibus V.A. Tillering responses of Lolium multiflorum plants to changes of red/far red ratio typical of sparse canopies. J. Exp. Bot. 1987;38:1432-1439.[Abstract/Free Full Text]
• Corkill L., Williams W.M., Lancashire J.A. Pasture species and cultivars for regions. Proc. N.Z. Grassl. Assn. 1981;42:100-122.
• Davies A. Leaf tissue remaining after cutting and regrowth in perennial ryegrass. J. Agric. Sci. (Cambridge) 1974;82:165-172.
• Easton H.S. Ryegrasses. In: Wratt G.S., Smith H.C., eds. Plant breeding in New Zealand. Wellington, NZ: Butterworths and Dep. of Scientific and Industrial Research, 1983:229-236.
• Gautier H., Varlet-Grancher C., Hazard L. Tillering responses to light environment and to defoliation in populations of perennial ryegrass (Lolium perenne L.) selected for contrasting leaf length. Ann. Bot. (London) 1999;83:423-429.[Abstract/Free Full Text]
• Hazard L., Ghesquière M. Productivity under contrasting cutting regimes of perennial ryegrass selected for short and long leaves. Euphytica 1997;95:295-299.
• Hazard L., Ghesquière M., Barraux C. Genetic variability for leaf development in perennial ryegrass populations. Can. J. Plant Sci. 1996;76:113-118.
• Hunt W.R., Easton H.S. Fifty years of ryegrass research in New Zealand. Proc. N.Z. Grassl. Assn. 1989;50:11-23.
• Kays S., Harper J.L. The regulation of plant and tiller density in a grass sward. J. Ecol. 1974;62:97-105.
• Langer R.H.M. Tillering in herbage grasses. Herb. Abstr. 1963;33:141-148.
• Lemaire G., Chapman D. Tissue flows in grazed plant communities. In: Hodgson J., Illius A.W., eds. The ecology and management of grazing systems. Wallingford, UK: CABI, 1996:3-36.
• Lonsdsale W.M., Watkinson A.R. Light and self-thinning. New Phytol. 1982;90:431-445.
• Matthew C., Lemaire G., Sackville Hamilton N.R., Hernandez-Garay A. A modified self-thinning equation to describe size/density relationships for defoliated swards. Ann. Bot. (London) 1995;76:579-587.[Abstract/Free Full Text]
• Matthew C., Yang J.Z., Potter J.F. Determination of tiller and root appearance in perennial ryegrass (Lolium perenne) swards by observation of the tiller axis, and potential application in mechanistic modelling. N.Z. J. Agric. Res. 1998;41:1-10.
• Neuteboom J.H., Lantinga E.A. Tillering potential and relationship between leaf and tiller production in perennial ryegrass. Ann. Bot. (London) 1989;63:265-270.[Abstract/Free Full Text]
• Neuteboom J.H., Lantinga E.A., Van Loo E.N. The use of frequency estimates in studying sward structure. Grass Forage Sci. 1992;47:358-365.
• Robson M.J. A comparison of British and North-African variety of Tall fescue (Festuca arundinacea). I. Leaf growth during winter and the effects on temperature and day length. J. Appl. Ecol. 1967;4:475-484.
• Simon J.C., Lemaire G. Tillering and leaf area index on grasses in the vegetative stage. Grass Forage Sci. 1987;42:373-380.
• Skinner R.H., Nelson C.J. Estimation of potential tiller production and site usage during tall fescue canopy development. Ann. Bot. (London) 1992;70:493-499.[Abstract/Free Full Text]
• Skinner R.H., Simmons S.R. Modulation of leaf elongation, tiller appearance and tiller senescence in spring barley by far-red light. Plant Cell Environ. 1993;16:555-562.
• Thom E.R., Waugh C.D., McCabe R.J. Growth and persistence of perennial and hybrid ryegrasses when grazed by dairy cows in the central Waikato region of New Zealand. N.Z. J. Agric. Res. 1998;41:477-486.
• Van Loo E.N. Tillering, leaf expansion and growth of plants of two genetic lines of perennial ryegrass grown using hydroponics at two water potentials. Ann. Bot. (London) 1992;70:511-518.[Abstract/Free Full Text]
• Zarrough K.M., Nelson C.J., Sleper D.A. Interrelationships between rates of leaf appearance and tillering in selected tall fescue populations. Crop Sci. 1984;24:565-569.[Abstract/Free Full Text]

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