Predicting anthesis date of perennial ryegrass (Lolium perenne L.) with growing degree‐days at heading

The agronomic significance of heading date in crop species is well documented; however, the date of anthesis is often less emphasized even though it has important applications for seed quality and yield. Moreover, the relationship between heading and anthesis is not well defined. We propose that growing degree‐days to heading can be used as a good predictor of anthesis date. Using a broad range of 520 diploid perennial ryegrass accessions, anthesis was found to be highly correlated with growing degree‐days to heading, and growing degree‐days to heading could be used to predict anthesis date in historical data sets collected over many years. The ability to adequately predict anthesis will allow seed‐producing farmers to improve seed quality by identifying times when high disease pressure will coincide with anthesis, thus allowing control measures to be applied.     

Genome-wide markers for seed yield and disease resistance in perennial ryegrass

The market success of perennial ryegrass(Lolium perenne L.) cultivars depends on sufficient seed production, as they are propagated by seed. However, breeding for high quality forage production reduces seed yield, and breaking the negative correlation would help to overcome the problem. The foliar disease crown rust is another factor affecting reproductive capacity and thereby seed yield. We evaluated seed yield-related traits and resistance to crown rust in a collection of commercial cultivars and ecotypes of perennial ryegrass and identified genome-wide markers associated with the traits. The study revealed high variation between the ecotype and cultivar groups as well as between years. A genome-wide association study identified 17 DNA single-nucleotide polymorphisms(SNPs) of which eight were associated with crown rust and nine with flag-leaf length. The SNP markers were located within or near predicted genes functioning in defense against pathogens. The identified genes are strong candidates for a further in-depth functional study to continue unravel determination of leaf architecture and crown rust resistance in perennial ryegrass.     

Effect of heading date of perennial ryegrass cultivars on tillering and tiller development in spring and summer

Three cultivars (two diploid and one tetraploid) in each of three maturity groups (early, intermediate and late) of perennial ryegrass were sown in 10 m² plots, replicated four times, in Northern Ireland in June 1997 in a study of the effect of heading date on tiller development (including initiation to flower) and turnover of tillers produced at specific times in spring in 1998 and 1999. The plots were harvested seven times in each year. Annual dry‐matter production was similar for all groups in each year. In spring and early summer of both years, tiller density of the diploid cultivars was 1·5 times greater than that of the tetraploid cultivars and the mean tiller density over all swards in June was about 0·40 times greater than that in April. Maximum proportions of reproductive tillers in the early, intermediate and late maturity groups, determined from apical dissections, were found in early April, mid‐May and early June, respectively. Although a high proportion of tillers, which were present when annual observations commenced in spring, was decapitated at the first harvest in the early group, the previous population density was maintained by rapid production of new tillers during May, including those from suppressed tiller buds during reproduction. It is concluded that the relationship between heading date and rate of tiller turnover (including flowering) at specified times in spring is important in sward management throughout the early part of the growing season and should be taken into account in tiller‐based grass growth models.     

Herbicides and seed production by two perennial ryegrass cultivars grown in weed-free conditions

The effects of five herbicides on seed yield and viability of perennial ryegrass cv. S24 were tested at two sites. Benzoylprop-ethyl, chlorfenpropmethyl, difenzoquat, ethofumesate and flam-prop-isopropyl were safe to use at doses recommended for use in other crops. When applied at three times the recommended dose, only difenzoquat reduced the yield and germination of seed and benzoylprop-ethyl reduced seed germination. The recommended doses of difenzoquat and ethofumesate were safe when applied on cv. Barlenna at different growth stages. Difenzoquat reduced seed yield only after three times the recommended dose was applied to tillered plants. Ethofumesate, even at three times the recommended dose, did not affect seed yield but plant numbers were reduced by early treatment. The results suggest that the herbicides tested may be safe to use in perennial ryegrass seed crops at the recommended doses but more work is needed on the safety of difenzoquat in relation to crop growth stage.     

Relationships and influence of yield components on spaced-plant and sward seed yield in perennial ryegrass

Adequate seed production is essential for cultivar success in perennial ryegrass turf and forage industries, but improvement is limited by the complexity of yield components and low-rank correlations between selection and production environments. This study examined seed yield components among 20 perennial ryegrass entries in both spaced plantings (selection environment) and swards (production environment) at two locations in Minnesota. Competitive (23 plants/m²) and non-competitive (3 plants/m²) spaced-plant nurseries were tested. Competitive spaced-plant total yield was highly correlated with sward yield (r_s = 0.64 and 0.66, p < 0.01) at both locations, whereas the non-competitive environment showed no correlation. Structural equation modelling (SEM) was used to explore the indirect and direct relationship of fall vegetative growth, winterkill, and yield components on total seed yield in all environments. Fertile tiller number (spikes plant⁻¹/m⁻²) exhibited both strong direct and indirect influence on total seed yield in all environments. However, the importance of fertile tiller number in the SEM was reduced with increased plant competition. The SEM showed that both weight per spike and seed yield per spike influenced total yield in spaced plants; however, neither consistently predicted total sward yield. The ratio of these two traits (g seed spike⁻¹/g spike⁻¹) gave an index of fertility that was easy to measure and had a superior correlation with sward yield at two locations (r_s = 0.81 and 0.54, p < 0.05) when spaced plants were under competition. Results suggest that increasing competition in spaced plantings and selecting for spike fertility may more accurately identify superior plant material compared to lower competition environments.     

The relationship between tiller appearance in spring and contribution to dry-matter yield in perennial ryegrass (Lolium perenne L.) cultivars differing in heading date

The relative contribution of tillers present in April and those appearing in consecutive periods in spring was assessed for perennial ryegrass cultivars in the three maturity groups (early, intermediate‐ and late‐heading). Each group was represented by two diploid and one tetraploid cultivar each in plots in their third (2000) and fourth (2001) harvest years in three replicated blocks receiving an average of 325 kg N ha^?1 and cut seven (in 2001) or eight (in 2000) times annually. ‘Main’ tillers and their daughters were marked with colour‐coded PVC‐covered wire loops in early April as were daughters which appeared in consecutive periods between harvests, the loop colour identifying the period of origin of the tiller. Tillers were harvested at cutting height (5 cm) before the plots were harvested and the herbage from tillers with the same colour code bulked per plot. Tillers were identified retrospectively as ‘reproductive’ if they had been decapitated at the previous harvest. Dry‐matter yield was higher in the early than late‐heading cultivars in April and early May but this was reversed in harvests in late May and June. The early heading group had a lower lamina content than the late‐heading group during reproduction growth, both due to the reproductive tillers (mainly those which overwintered) having a lower leaf content and to their being fewer and smaller vegetative tillers during the reproductive phase than for the late‐heading group. Turnover of tillers was high in spring due to decapitation of reproductive tillers and rapid post‐flowering tillering. This was particularly pronounced in the early heading group which also had slightly more tillers marked in April which were subsequently decapitated than in the other maturity groups, i.e. 0·56 compared with 0·44 for the late‐maturing group. Mean ratios of rate of death: rate of tillering for 3 years (1999–2001) for the early and late‐heading groups were 0·8 and 0·4, respectively, for April–May and 1·1 and 2·4, respectively, for June indicating the different patterns in tiller turnover for the two extreme maturity groups. Information on tiller origin and contribution to yield can be used to refine tiller‐based grass growth models.     

Effect of temperature regime on germination of seed of perennial ryegrass (Lolium perenne)

Perennial ryegrass ( Lolium perenne L.) is one of the most valuable temperate pasture grasses in the world. Understanding seed germination in response to temperature can help determine its optimal seeding times. Germination tests for two cultivars of perennial ryegrass (cv. 'Turfstar' and cv. 'Transtar') were conducted by applying thirty-six constant and alternating temperature regimes, ranging from 5 to 40°C (16 h night/8 h day). Responses in germination rate to these temperature regimes were then used to construct a quadratic response surface, giving estimated germination rates with confidence intervals at P  ≤   0·05 for both cultivars. Optimum germination rate occurred over a range of regimes: 15/25, 20/25, 20/30 and 25/30°C. Furthermore, a wide range in diurnal alternating temperatures resulted in maximum seed germination rate for cv. 'Transtar', while no constant temperature regime supported maximum germination rate for cv. 'Turfstar'. A temperature-dependent germination rate function for perennial ryegrass was developed which could be used in the future to predict location-specific optimum seeding times when national or regional monthly temperature data are available.     

De-hardening in contrasting cultivars of timothy and perennial ryegrass during winter and spring

Scenarios of climate changes indicate longer and more frequent spells of mild weather during winter in northern latitudes. De-hardening in perennial grasses could increase the risk of frost kill. In this study, the resistance to de-hardening of different grass species and cultivars was examined, and whether the resistance changes during winter or between years, was tested. In Experiment 1, two cultivars of timothy ( Phleum pratense L.) and perennial ryegrass ( Lolium perenne L.) of contrasting winter hardiness were grown under ambient winter conditions, transferred from the field in January and April 2006 to the laboratory for 9 d with controlled de-hardening conditions of 3°C, 9°C and 15°C. The timothy cultivars were tested at 3°C, 6°C and 9°C in a similar experiment (Experiment 2) in January 2007. De-hardening, measured as decrease in frost tolerance (LT₅₀), was less in timothy than in perennial ryegrass and increased with increasing temperatures. The northern winter-hardy cultivar Engmo of timothy de-hardened more rapidly than the less-hardy cultivar Grindstad, but had higher initial frost tolerance in both experiments, whereas there was less difference between cultivars of perennial ryegrass in Experiment 1. Cultivar Grindstad of timothy lost all hardiness in early spring at all temperatures, whereas cultivar Engmo maintained some hardiness at 3°C. Cultivar Engmo de-hardened at a lower rate in 2007 than in 2006, in spite of similar frost tolerance at the start of de-hardening treatment in both years. This indicates that the rate of de-hardening was controlled by factors additional to the initial frost tolerance and that autumn weather conditions might be important for the resistance to de-hardening.     

Determination of microbial protein in perennial ryegrass silage

The microbial matter fraction was determined in perennial ryegrass silages of different dry-matter (DM) contents, ensiled with or without Lactobacillus plantarum . ¹⁵N-Leucine and the bacterial cell wall constituent diaminopimelic acid (DAPA) were used as markers for microbial-N. Perennial ryegrass crops with DM contents of 202, 280 or 366 g kg⁻¹ fresh weight were ensiled in laboratory-scale silos and stored for 3 to 4 months. At different times after ensiling, silages were analysed and microbial fractions were isolated. Microbial-N concentration determined with ¹⁵N-leucine reached a maximum during the first week of ensilage. It remained unchanged thereafter, except in silage with a DM content of 280 g kg⁻¹ in which it decreased ( P  < 0·01) by 32% during storage. After 3 to 4 months ensilage, microbial-N concentration varied from ≈0·3 to ≈1·7 g kg⁻¹ DM. A negative relationship was observed between microbial-N concentration and silage DM content. Inoculation resulted in an approximately twofold increase ( P  < 0·001) in microbial-N concentration. Microbial-N concentrations determined with DAPA were 1·14–2·07 times higher than those determined with ¹⁵N-leucine. However, 19–35% of the DAPA in silage occurred in a soluble form, indicating that this fraction of DAPA was not associated with intact bacteria.     

The optimal lignin quantification method to breed for an improved cell wall digestibility in perennial ryegrass

Perennial ryegrass (Lolium perenne) is an important source of protein and energy for dairy cattle. To improve the protein/energy ratio of this forage, focus is now on improving its cell wall digestibility. The in vitro assessment of the digestible fraction of the neutral detergent fibre (NDFD) is a superior method for determining the cell wall digestibility, but requires the use of ruminal fluid, which has a highly variable composition and is often not readily available. As lignin is considered the main cell wall component that impedes NDFD, we investigated whether this “subtrait” could serve as alternative breeding selection criterion to improve NDFD. Therefore, we assessed the accuracy of two lignin quantification methods: van Soest (ADL) and Klason lignin (KL). We also considered KL estimates corrected for the solubilized lignin (total lignin or TL) and non‐solubilized protein (TL'). Although the latter is considered the truest possible lignin content, it was not always the most correlated to NDFD, due to the limited accuracy of protein quantification on lignin residue. TL is most correlated to NDFD and we therefore recommend it for use in conventional breeding if NDFD determination is not a possibility. However, NDFD is still a superior selection criterion, as it combines the effect of several subtraits and not just lignin. For marker–trait association studies, a more accurate estimate of lignin content is more important than a high correlation with NDFD, but also here, TL performs best.     

Comparison of the performance of dairy cows offered kale,swedes and perennial ryegrass herbage in situ and perennial ryegrass silage fed indoors in late pregnancy during winter in Ireland

The effects on the performance of dairy cows offered kale, swedes, and perennial ryegrass in situ and perennial ryegrass silage fed indoors to dairy cows pre‐partum during winter in Ireland was examined. Eighty‐eight spring‐calving dairy cows were randomly assigned to one of four offered treatments; (i) 8 kg of dry matter (DM) of kale leaf and stem + 4 kg DM of perennial ryegrass silage (treatment K), (ii) 8 kg DM of the root and leaf of swedes + 4 kg DM of perennial ryegrass silage (treatment S), (iii) 12 kg DM of perennial ryegrass herbage (treatment G) offered in situ and (iv) perennial ryegrass silage offered ad libitum indoors (treatment ID). Cows on treatments K, S and ID had a greater (P < 0·001) increase in body condition score (0·20, 0·14 and 0·50 units respectively) pre‐partum than cows on treatment G which lost 0·22 units. Pre‐partum treatment had no effect on variables of milk production in the following lactation. In the first 100 d of lactation, cows on treatment G pre‐partum had a lower milk fat concentration (35·6 g kg^?1) compared with cows on treatments S and ID (38·3 and 39·3 g kg^?1 respectively). There was no effect of treatment on the intervals between parturition and first insemination (mean 74·6 d) and conception (mean 96·1 d). The results suggest that offering kale and swedes to dairy cows pre‐partum resulted in a similar lactation performance to dairy cows grazing a perennial ryegrass sward or offered perennial ryegrass silage indoors.     

Tolerance to frost and ice encasement in cultivars of timothy and perennial ryegrass during winter

Ice encasement causes major winter damage in grasslands in coastal areas of Northern Scandinavia and may also affect grass performance in a future changing climate. Changes in ice‐encasement tolerance (LD50), frost tolerance (LT50) and water‐soluble carbohydrate (WSC) content were investigated in different cultivars of timothy and perennial ryegrass sampled at three sites with contrasting conditions. Timothy endured ice encasement for 40 d more than ryegrass (maximum LD50 63 vs. 20 d), and a cultivar originating from 69°N tolerated significantly longer periods in ice than a cultivar from 59°N. A similar relationship between cultivar origin and tolerance was observed for ryegrass. The higher LD50 in timothy compared with ryegrass seemed to be associated with a lower rate of change in WSC content during ice encasement, but no apparent relationship was found between WSC content at the start of encasement and plant survival in ice. A significant linear relationship was found between LD50 and LT50 of plants sampled in the field. A differing decline in frost tolerance during ice encasement for the species indicated that timothy is more resistant to dehardening under ice than ryegrass. This study contributes data and functional relationships needed to develop models of grass performance during winter.     

Impact of frost and plant age on compensatory growth in timothy and perennial ryegrass during winter

Two cultivars of each of two contrasting grass species, timothy ( Phleum pratense L.) and perennial ryegrass ( Lolium perenne L.), sown either in May or July, were sampled for dry matter (DM) weight of roots and herbage in late October (end of main growing season) and examined for regrowth when exposed to a frost treatment (−8 to −10°C in darkness for 48 h) in late January, early March and late April. The frost treatment caused compensatory root and herbage growth, and regrowth of roots in March and April was greater than regrowth of herbage. Early-sown plants had higher DM weights of roots and herbage than late-sown plants in October but had the lowest survival rate when exposed to the frost treatment in April. Compensatory growth of root and herbage in response to moderate frosts occurred in January and March in all cultivars, and in the most frost-resistant timothy cultivar in April. Concentration of total carbohydrates increased from October to March with the greatest increase in the most winter-hardy cultivar of each species, and then decreased in April. An indirect correlation between concentration of total carbohydrates and tolerance to moderate frost was indicated, and plant survival and ability for compensatory growth were also associated with differences in adaptation related to winter survival in the cultivars tested.     

Natural diversity in vegetative and reproductive investments of perennial ryegrass is shaped by the climate at the place of origin

In forage grasses, vegetative and reproductive investments are major determinants of yield and persistence. A survey of the diversity of vegetative and reproductive investment traits was carried out on 213 perennial ryegrass genotypes, representing 51 natural European accessions. Plants were phenotyped for traits related to leaf elongation, tillering, reproductive investment and heading date, at two locations with markedly different climates. Strong genetic effects for all traits were found. Interactions between genotype and location were moderate. Plants showed stronger spring leaf growth, lower numbers of tillers and higher reproductive investments at Lusignan (France) than at Melle (Belgium). Plant growth rate and tillering capacity were genetically nearly independent suggesting breeding for both traits simultaneously and independently should be possible. A high genetic diversity was observed for all traits. This diversity was structured in three main clusters. One cluster comprised early‐flowering genotypes with high reproductive investments and high spring growth rates. The remaining genotypes fell into two clusters based on differences in tillering capacity. Clear links were found between traits and the climatic conditions of the region of origin of the accessions. Autumn growth rate was positively correlated with solar radiation at the region of origin in October and February.     

The contribution of perennial ryegrass (Lolium perenne L.) breeding to whole pasture productivity under dairy cattle grazing in New Zealand. 2. Rates of gain in production traits and economic value

Perennial ryegrass (Lolium perenne) plant breeding has delivered several high performing and broadly adapted cultivar-endophyte (Epichloë) combinations for the New Zealand pasture-based livestock industries. However, the trends in key traits and the potential economic value being added to farm systems have not previously been addressed systematically. Rates of gain in yield, nutritive value, phenological and morphological traits, and the economic value of those traits, were estimated among and within ryegrass functional groups (heading date, ploidy) traded commercially between 1973 and 2012. Whole pasture dry matter yield improvements of c. 80 and 60 kg DM/ha per year were identified in in late-season heading diploids and tetraploids respectively. Trends in metabolisable energy were negative within functional groups, but positive when all cultivar-endophyte combinations were included in the analysis due to the addition of tetraploids and late-season heading diploids from the mid-1990s. The estimated trend in overall economic value (all cultivar-endophyte combinations included) was $7/ha per year based on DM yield only, about half the rate of gain previously estimated using small-plot merit testing data. The trend increased to $15/ha per year when ME was included due to the emergence of commercial tetraploids from the early 2000s onwards. Estimated economic gains were high within late-season heading diploids and tetraploids but not mid-season diploids. These trends suggest that, if high performing cultivar-endophyte combinations had been adopted in New Zealand dairy systems, then pasture utilization should have increased by ~1 t DM/ha above the current industry average. Reasons for this apparent discrepancy are discussed.     

The response of a perennial ryegrass (Lolium perenne L.) seed crop to nitrogen fertilizer application in the absence of moisture stress

Responses of perennial ryegrass (Lolium perenne L.) to nitrogen (N) fertilizer application rates and timings vary widely, because water is often limiting. Yield response to N fertilizer application during autumn, late‐winter and spring, and the associated efficiency of use of these inputs, was assessed under conditions of non‐limiting soil moisture during two, one‐year lysimeter studies in Canterbury, New Zealand. There were significant (P < 0·05) increases in seed and herbage yields with increasing N fertilizer application. Seed yields differed with year; greatest yields were 300 g m^?2 in 1996 and 450 g m^?2 in 1997. Seed head numbers (r²=0·77), seeds head^?1 (r²=0·92) and herbage yield (r²=0·92) were the major determinants of seed yield in both years. Irrigation required to maintain the soil between 70% and 90% of field capacity was directly related (r²=0·94 and 0·99 in 1996 and 1997 respectively) to increases in herbage yield. Seed yield, seed quality (thousand seed weight and percentage of seed > 1·85 mg), efficiency of water use, efficiency of N fertilizer use and apparent N fertilizer recovery were greatest when N fertilizer was applied at a rate of 50 kg N ha^?1, 50 or 100 kg N ha^?1 and 150 kg N ha^?1 in autumn, late‐winter and spring respectively; further increases in spring N fertilizer stimulated vegetative growth, but not seed yield. As a management strategy, applying N fertilizer to match the N requirements of the crop during the reproductive stage of growth will result in high yields of high quality seed while minimizing environmental impact.     

Effects of perennial ryegrass (Lolium perenne L.) cultivars on herbage production, nutritional quality and herbage intake of grazing dairy cows

Four perennial ryegrass (Lolium perenne L.) cultivars were compared for differences in herbage production, nutritive value and herbage intake of dry matter (DM) during the summers of 2002 and 2003. Two paddocks were sown with pure stands of four cultivars in a randomized block design with three replicates. Each plot was subdivided into fourteen subplots (22 m × 6 m) which were grazed by one cow during 24 h. Twelve lactating dairy cows were assigned to one cultivar for a period of 2 weeks in a 4 × 4 Latin square experimental design; the experiment lasted 8 weeks in each year. Sward structure (sward surface height, DM yield, green leaf mass, bulk density and tiller density) and morphological characteristics were measured. The ash, neutral‐detergent fibre, acid‐detergent lignin, crude protein and water‐soluble carbohydrate concentrations, and in vitro digestibility of the herbage were measured. The sward was also examined for infestation by crown rust (Puccinia coronata f. sp. lolii). Herbage intake of dairy cows was estimated using the n‐alkane technique. Cultivar differences for all sward structural characteristics were found except for bulk density and tiller density in 2003. Cultivars differed for proportions of pseudostem, stem (in 2003 only) and dead material. The chemical composition of the herbage was different among cultivars, with the water‐soluble carbohydrate concentration showing large variation (>0·35). Cultivars differed in susceptibility to crown rust. Herbage intake differed among cultivars in 2002 (>2 kg DM) but not in 2003. Herbage intake was positively associated with sward height, DM yield and green leaf mass. Canopy morphology did not affect herbage intake. Crown rust affected herbage intake negatively. It was concluded that options for breeders to select for higher intake were limited. High‐yielding cultivars and cultivars highly resistant to crown rust were positively related with a high herbage intake.     

Changes in stubble carbohydrate content during regrowth of defoliated perennial ryegrass (Lolium perenne L.) on two nitrogen levels

Changes in stubble carbohydrate content during the regrowth of ryegrass ( Lolium perenne L.) grown under hydroponic conditions at two nitrogen levels were studied as a function of time by high-performance liquid chromatography. Experimental data showed that regrowth at a non-limiting nitrogen level (1·0 mol m⁻³ NH₄NO₃) involved two different physiological periods. The first occurred during the first 6 d and was characterized by the mobilization of 60 to 90% of the soluble carbohydrates (i.e. glucose, fructose, sucrose, oligofructans and polyfructans). During the second period (6.28 d of regrowth) carbohydrate contents rose to the values observed prior to cutting (20% of dry matter at the 28th d of regrowth).
The effect of low nitrogen conditions (0·2 mol m⁻³ NH₄NO₃) was observed only during the second phase. Plants regrown in a nitrogen-starved medium accumulated 2·3-fold more polyfructans than plants regrown in a non-limiting nitrogen medium. Their fructose and glucose contents remained at 2% of dry matter from the end of the first phase of mobilization.
The experimental results are interpreted and discussed in terms of the existence of two distinct fructan synthetic pathways.     

Soil N contributes to the oscillations of the white clover content in mixed swards of perennial ryegrass under conditions that simulate grazing over five years

The effect of the initial N-supplying capacity of soils (SoilN, 90–230 kg N ha^–1 year^–1) was tested on the dry-matter and N yields of pure or mixed white clover and perennial ryegrass swards, managed under simulated grazing over a 5-year period. The cumulated N harvested in the mixed swards was similar, both for white clover and perennial ryegrass, but the proportion of white clover showed oscillations over a 2-year period. In the first year, the SoilN effect was similar to that of fertilizer N. During the course of the experiment, the effect was always positive on the pure perennial ryegrass sward, alternately negative and nil for the white clover in the mixed sward and alternately positive and nil for the perennial ryegrass in the mixed sward; the period of these oscillations was 2 years. From the third regrowth period after sowing, the ratio between the actual N concentration and the concentration non-limiting to growth for the perennial ryegrass in the mixed sward, increased above that of the pure perennial ryegrass sward. It was in turn greater in the soils that were initially poor and then greater in those that were initially rich in soil N. The periodic oscillation of the initial SoilN effects implies that the initial SoilN gradient was alternately compensated and restored. It was concluded that N fluxes are partly responsible for the temporal oscillations in the proportion of white clover in mixed swards.     

Between-cultivar variability in breaking force of components of perennial ryegrass (Lolium perenne)

The variation in force required to break the leaves and pseudostems of perennial ryegrass ( Lolium perenne ) was measured on twelve New Zealand commercial and pre-release cultivars using a punch and die apparatus which enabled up to 100 simultaneous breaks per sample. Perennial ryegrass cultivars were sampled from 2-year-old pure swards in two studies carried out in spring and autumn. In the first study, the forces required to break old and young leaves, and pseudostems, of six cultivars ranging in heading date and ploidy were compared at a designated morphological stage during spring growth. Force was measured as Newtons (N) mg⁻¹ dry matter (DM) and the difference between the force required to break leaves and pseudostems was significant ( P  < 0·01). The youngest emerged leaf required a greater force by 0·13 than the oldest green leaf (5·60 and 4·90 N mg⁻¹ DM for young and old leaf respectively). The force required to break leaves (average of young and old leaves) of 5·25 N mg⁻¹ DM was 0·12 greater than the force required to break pseudostems (4·59 N mg⁻¹ DM). This difference was consistent across most cultivars. In the second study, the force required to break leaves of ten cultivars was tested daily over three autumn periods when all cultivars were sampled at a regrowth age of 2 weeks. The cultivar Nevis was used in each period whilst the other cultivars were used in one period. When averaged across periods, cultivars could be separated into three groups of high, medium and low forces required to break leaves. The difference between the means of the high and low groups was 0·33 with a range from 3·29 to 4·91 N mg⁻¹ DM.