Strains Of Subterranean Clover Research Articles

Studies in uterotrophic activities in strains of subterranean clover

Uterotrophic responses in ovariectomized ewes when fed or grazed on Mount Barker, Yarloop or Dwalganup varieties of subterranean clover are reported. The high formononetin varieties Dwalganup and Yarloop always elicited a uterotrophic response. The low-formononetin, high-genistein and biochanin A variety, Mount Barker, stimulated a uterotrophic response, using a 5-day bioassay, when fed at 200g/day or 800g/day, but little or no response when grazed. When chopped lucerne hay was offered with 200 g of the Mount Barker the uterotrophic response was suppressed and the mean uterine weight was not significantly different from that of the negative controls (P= 0.57). The uterine weight of sheep eating 200 g/day of Yarloop and offered lucerne chaff or pellets in one experiment was lower (but not significantly lower) than the unsupplemented group. This trend may be worthy of further investigation.

The effect of defoliation on seed yield of two strains of subterranean clover grown in monocultures and in binary mixtures

The effect of defoliation on seed production was examined in swards of Seaton Park and Midland B grown in a de Wit replacement series in the field. The three defoliation treatments were: D0, uncut (control); D1, defoliated at weekly intervals until the beginning of flowering; and D3, as for D1 but with cutting continued until the end of flowering. Defoliation up to the commencement of flowering (D1) had no significant effect on seed yield in the monocultures of either strain. However, with severe defoliation (D3) seed yields were reduced in both strains, although more so in Midland B than in Seaton Park. This greater sensitivity of Midland B supports the results of earlier work. The most important finding from this study was that cutting influenced the competitive relations between the two strains. For both the D0 and D1 treatments there was competition for the same resources ('space' of de Wit); in D0 neither strain had a competitive advantage, whereas in D1 Midland B appeared to be the better competitor. By contrast, in the D3 treatment there was the relatively unusual case of competition for resources which were not entirely the same; and here Seaton Park was the better performer. Possible explanations for this response are suggested.

The winter production of some strains of subterranean clover grown in defoliated swards

The results of two experiments are reported, one at Perth, Western Australia, in an open-sided glass shelter, and the other at Wagga Wagga, New South Wales, in the open. Clover swards were grown in boxes and after about one month were subjected to weekly, close defoliation. Two strains that differ in growth habit, Woogenellup (relatively erect) and Esperance (compact, lowgrowing), were used in both experiments. In addition, strain 209.8.19.1 (a crossbred similar to Esperance) was included at Perth, and Nungarin, Yarloop and Larisa at Wagga Wagga. The main finding was that winter production differed little, if at all, between the strains. The relevance of the results to the field evaluation of clover strains is emphasized, and we suggest that under good conditions of moisture supply, nutrition, plant density, etc., substantial differences between strains in winter production are unlikely

Relations between stocking rate, environment and scorch disease on grazed subterranean clover pasture in Western Australia

The effects of weather on clover scorch disease caused by Kabatiella caulivora, the effects of the disease on pasture and sheep production, and the effect of sheep stocking rate (6, 8, 10 and 12 sheep/ha) on the disease were studied in a field experiment over three seasons near Albany, Western Australia. Spraying with benlate was used to control clover scorch on some treatments. Mean temperatures during the period when symptoms of the disease increased were in the range 11-17�C. Rainfall was frequent each year during the same period. The rapid increase in disease symptoms was observed when pasture dry matter on offer was approximately 2500 kg/ha. Disease symptoms decreased during a period of water stress of the pasture. Clover scorch disease had no consistent effect on pasture or animal production except that pasture dry matter on offer in spring was reduced in the unsprayed treatments at the lower stocking rates in the second two years. Higher stocking rates (10 and 12 sheep/ha) reduced the level of clover scorch symptoms without the use of chemical control with benlate. At the period of peak scorch symptoms a stocking rate of 10 sheep/ha reduced disease incidence by 20-35% compared with 6 sheep/ha in unsprayed plots. Increased sheep stocking rates are suggested as a possible alternative to chemical control or replacement of susceptible strains of subterranean clover in grazed pasture.

An analysis of seed yield in some strains of subterranean clover (Trifolium subterraneum L.) when grown in binary mixtures

Two experiments using various strains of subterranean clover are described. The first experiment was conducted in the field with mixtures of Dwalganup/Northam A, DwalganupI/Daliak and Yarloop/Seaton Park, and the second in an open-sided glasshouse with Yarloop/Seaton Park. In the field experiment, the plots were grazed continuously from late July until early November when the swards were completely dry; in the glasshouse experiment, the swards were defoliated weekly until shortly after the beginning of flowering. Mixtures were arranged according to the de Wit replacement series. Seed yields for the Dwa1ganup/Northam A mixture showed the classical (de Wit) competition for the same resources, with Northam A the better competitor. On the other hand, for the Dwalganup/Daliak and Yarloop/Seaton Park mixtures there was no clear evidence of a competitive advantage of one strain over the other pair member, at least under our defoliated conditions. Whether or not this absence of 'competition' (as usually understood) is common in clover-strain mixtures is as yet unknown. We emphasize, however, that long-term success of clover strains in mixtures is not invariably associated with competitive advantage.

The effects of length of growing season, with and without defoliation, on seed yield and hard-seededness in swards of subterranean clover

The effects of length of growing season and defoliation on seed yield and hard-seededness were examined in two strains of subterranean clover (Seaton Park, Midland B) grown in swards in the field. All plots were sown at the same time and the length of growing season was varied by altering the time of finish of the season (by withholding water). There were three length of growing season treatments: T1 (short), T2 (intermediate) and T3 (control). The defoliation treatments were D0, uncut (control), and D1, defoliated at weekly intervals until the commencement of flowering. Reducing the length of growing season drastically reduced seed yield. Thus when the growing season was only 3 weeks shorter than the control (i.e. T2 compared with T3), seed yields averaged over strains and defoliations were reduced by at least one half. With a further reduction of 2 weeks in the length of the season (T1) seed yields were only about one-third of those obtained in the control (T3). The reductions in seed yield were due to reductions in both the number of mature burrs produced and to a lesser extent in mean weight per seed. Although defoliation increased seed yield in all growing seasons, the effect when measured on a relative scale was greater in T2 than in either T1 or T3. But on an absolute scale the size of the response was greater in T2 and T3 than in T1. The rate of breakdown of hard-seededness was faster in Seaton Park than in Midland B, but it decreased in both strains with increasing length of growing season.

The effects of a continued water supply during and beyond seed development on seed production and losses in subterranean clover swards

Four strains of subterranean clover were grown in swards and mown regularly until the beginning of flowering. During the period of flowering and seed development, the swards were irrigated as required to prevent moisture stress. Watering was then continued to keep the burrs and seeds moist for a further 5 months. Depending on the strain, seed yields reached a peak between 74 days and 86 days after the onset of flowering (late August-early September). Then followed a sudden and marked decline in both the amount and number of seeds present in the four strains. By the end of February less than 20% of the seeds produced were still present in the soil. Seed germination accounted for less than 50% of the seed losses. The remainder (unrecovered seed) was presumably lost as a result of attack by pathogenic microorganisms in the soil. The results suggest that it may be difficult to obtain maximum seed yields in swards of subterranean clover. Even a relatively small (3 weeks) decrease or increase in the period for which moisture is available, compared with the optimum, can lead to markedly reduced seed yields.

The responses to defoliation of two strains of subterranean clover, differing in growth habit, when grown in swards

Dense swards of two strains of T. subterraneum-herein referred to as C and P-were compared at two heights of cutting-1.5 cm (low) and 5.0 cm (high)-and two frequencies of defoliation- 1-weekly (frequent) and 4- or 5-weekly (infrequent). Strain C has smaller leaves than P and a compact, in contrast to a lax, growth habit. The swards (initial density of c. 25 plants/dm2) were grown in boxes, out of doors, at Perth from 27 April to 20 September. Mean daily solar radiation varied from c. 10 to 16 MJ/m2 and average daily maximum and minimum temperatures were c. 20� and 10�C respectively. The principal finding was that under defoliation stress (i.e. low cutting) strain C yielded more than P, whereas at a lower level of stress (high cutting) there was usually little if any difference between these strains. This effect was established for the most part before the first harvest, at day 55; thereafter, with continued defoliation stress, strain P appeared to worsen slightly relative to C. The results provide support for the view that strains with a compact growth habit are less susceptible to defoliation (or grazing) stress than taller strains of lax growth habit. Generally, the total yield of tops and also the effective yield (as cut and removed material) decreased when cutting height was lowered. Also, infrequent cutting increased effective yield, particularly under low density (four plants/dm2) as observed in an ancillary experiment.

Are some strains of subterranean clover (T. subterraneum) highly susceptible to low temperature stress?

Two experiments, one with spaced plants and the other with swards, were conducted in a controlled-temperature glasshouse at Perth, Western Australia. Three strains-Phillip Island, CPI 18293 and CPI 68043H-were selected on the basis of field observations of apparent very poor winter growth in rows, and tested against Tallarook as a control. The temperature treatments were 22/17� (day/night) and 12/7�C. In the spaced plant experiment (occupying the first 48 days of growth), temperature and strain effects were highly significant, but there was no indication of a strain x temperature interaction. In the sward experiment (from days 51 to 77) temperature effects were small; and in only one strain, Phillip Island, was the decline in tops growth due to low temperature greater (P< 0.05) than for Tallarook. The experiments failed to provide support for the so-called 'winter dormancy' phenomenon. Possible explanations for the discrepancy between the present findings and the field observations are given.

Evolution of subterranean clover in South Australia. I. The strains and their distribution

The distributions of the strains of subterranean clover were determined from the presence of burrs in wool collected at the Adelaide Wool Sales. Of 7600 samples examined, nearly 1300 contained viable seeds. This seed was grown, the strains were identified, and their distributions in South Australia were mapped. Subterranean clover was found in wool from most areas with more than 400 mm of rain. However, it was absent from the climatically favourable Yorke Peninsula, and it seems clear that distribution of subterranean clover in South Australia is limited by the presence of alkaline soils. Divergent strains are widespread in South Australia. In all, 435 divergent strains were discovered from 325 farms. The presence of these strains leads us to believe that genetic change in subterranean clover, previously thought to be genetically stable, has been brought about by infrequent outcrossings, mainly in mixtures of cultivars. We discuss evidence for this proposal, and the consequences that it has for seed certification schemes. The distribution of flowering time amongst the divergent strains differed from the cultivars. Many of them flowered about half way between the mid-season cultivar Mount Barker and the early-flowering cultivar Dwalganup. There was no strain later than Tallarook, the latest-flowering cultivar, and very few earlier than Dwalganup. Flowering time of the divergent strains was weakly related to the length of growing season of the farms which produced the wool. Strains were also discovered which were morphologically identical with a cultivar but which flowered either earlier or later. The first-released cultivars, Mount Barker and Dwalganup, were the most widely distributed of all strains. Indeed success, in terms of the number of seeds of a cultivar found in the wool, could be broadly related to the number of years since release. The data illustrate the significance of the early-flowering cultivars on the distribution of subterranean clover, but indicate that, apart from T. brachycalycinum, there is little need in South Australia for yet earlier cultivars.

The influence of shading on seed yield in subterranean clover

Swards of three strains of subterranean clover (Woogenellup, Clare and Seaton Park) were subjected to three shading treatments (30%, 55% and 100% of daylight) from the beginning of flowering onwards. For the 100% daylight (unshaded) treatment the incoming daily solar radiation averaged between 20 and 30 MJ/m2. In the unshaded treatment, seed yields for the three strains ranged from about 120 to almost 200 g/m2. These yields were invariably decreased by shading. Moreover the evidence indicated a curvilinear relationship between seed yield and light supply such that at 50% of daylight there was a reduction of rather more than 50% in seed yield. Shading mainly affected the number of inflorescences produced per unit area, although other components of seed yield were also affected adversely. Even late shading (towards the end of flowering) led to lower seed yield, partly associated with lower inflorescence numbers and partly with lower seed numbers per burr. The results are considered to have significance for clover regeneration in mixed clover/grass pastures and also in the cloveritree associations of agro-forestry.

The effect of defoliation on inflorescence production, seed yield and hard-seededness in swards of subterranean clover

Swards of three strains of subterranean clover (Seaton Park, Yarloop, Midland B) were subjected to a range of defoliation treatments. In all strains, cutting at weekly intervals at a height of 1.5–2 cm from 1 month after sowing until the onset of flowering led to a slight delay in flower initiation but the time of flowering was little affected. The rate of inflorescence production, however, was always increased, as was the total number of inflorescences produced by the end of flowering. In particular, seed yields were increased by at least 30% compared with uncut controls. This effect was attributable partly to increased inflorescence numbers and partly to increases in other yield components as a consequence of the burial of a large proportion of burrs. Cutting increased the initial level of hard-seededness in Seaton Park and Yarloop; in addition the rate of breakdown of hard-seededness in all strains was slower in seed from the defoliated swards. When cutting was continued until midway through flowering (with the cutting height progressively raised) the seed yield in Yarloop and especially in Midland B was much lower than that obtained when cutting was stopped at the beginning of flowering; but in Seaton Park there was no reduction. With further cutting-until the end of flowering-seed yields were less than when cutting was stopped midway through flowering. Extending cutting into the flowering period (compared with cutting only until the onset of flowering) resulted in a decline in the initial level of hard-seededness and an increase in the rate of breakdown of hard-seededness in Midland B but had little effect in Yarloop or Seaton Park.

Corrigendum - The effect of defoliation on inflorescence production, seed yield and hard-seededness in swards of subterranean clover

Swards of three strains of subterranean clover (Seaton Park, Yarloop, Midland B) were subjected to a range of defoliation treatments. In all strains, cutting at weekly intervals at a height of 1.5–2 cm from 1 month after sowing until the onset of flowering led to a slight delay in flower initiation but the time of flowering was little affected. The rate of inflorescence production, however, was always increased, as was the total number of inflorescences produced by the end of flowering. In particular, seed yields were increased by at least 30% compared with uncut controls. This effect was attributable partly to increased inflorescence numbers and partly to increases in other yield components as a consequence of the burial of a large proportion of burrs. Cutting increased the initial level of hard-seededness in Seaton Park and Yarloop; in addition the rate of breakdown of hard-seededness in all strains was slower in seed from the defoliated swards. When cutting was continued until midway through flowering (with the cutting height progressively raised) the seed yield in Yarloop and especially in Midland B was much lower than that obtained when cutting was stopped at the beginning of flowering; but in Seaton Park there was no reduction. With further cutting-until the end of flowering-seed yields were less than when cutting was stopped midway through flowering. Extending cutting into the flowering period (compared with cutting only until the onset of flowering) resulted in a decline in the initial level of hard-seededness and an increase in the rate of breakdown of hard-seededness in Midland B but had little effect in Yarloop or Seaton Park.

The influence of defoliation on vegetation growth in swards of three strains of subterranean clover

Three defoliation regimes—uncut, defoliated every 14 days at 1.5 cm, and defoliated every three or four days (alternately) at 1.5 cm—were imposed on dense swards of Blackwood, Dwalganup and Daliak subterranean clover. The swards were grown in boxes, out of doors, at Perth from 1 June to 29 August. Mean daily solar radiation ranged from c. 1050 to 1450 J/cm2/day, and the average daily maximum and minimum temperatures were about 17° and 8.5°C respectively. The main finding was that defoliated swards yielded considerably less than uncut swards; averaging strains (and the two defoliated treatments) the decrease was c. 20% at day 33 and more than 40% at day 89. The lower yields of defoliated swards were associated with lower leaf area indices. During the first half of the experimental period, defoliation depressed growth in Blackwood more than in Dwalganup and Daliak. Uncut swards maintained the original plant density (28 plants/dm2), though some dead material was recorded in harvests at day 61 and (more particularly) day 89. Leaf area index exceeded 9 at day 89, with no clear optimum. Defoliated swards—especially those cut every three or four days—had more but smaller leaves, and higher branch numbers than uncut swards. In some respects these results conflict with those of previous reports, and explanations are proposed for apparent inconsistencies, mainly in terms of the temperature conditions.

The interrelation of burr burial, seed yield and dormancy in strains of subterranean clover

Prevention of burr burial drastically reduced the yield of viable seed in subterranean clover. This occurred through reductions in total burr number, number of mature burrs, number of seeds per burr, individual seed weight and seed viability. Strains differed markedly in their ability to produce seed in unburied burrs. A simple selection criterion based on changes in individual seed weight was proposed as a guide to screening for this character. When this criterion was applied to a wide range of strains, it appeared that later-maturing types were the most capable at producing seed in unburied burrs. The initial level of hardseededness was lower in seed from unburied burrs; also the rate of breakdown of hardseededness was faster in this seed, although the size of the effect varied between strains. Defoliation during the flowering period increased the initial level of hardseededness in seed from both buried and unburied burrs. Seed produced in buried burrs generally had a faster rate of breakdown of embryo dormancy than seed from unburied burrs, although the response varied between strains. The implications of these findings for future breeding and improvement in subterranean clover are discussed.

The acylated isoflavone glycosides from subterranean clover and red clover

Formononetin and biochanin A 7-O-glucosides (1a and 2a) and their malonate hemi-ester derivatives (1b and 2b) have been isolated from red clover and from the Yarloop strain of subterranean clover. Structure (2b) is a correction of an earlier structural assignment to this compound. Small amounts of the derived methyl esters (1c and 2c) are also present in both clovers. Similar derivatives of genistein have been obtained from the Yarloop strain, although only the 7-O-glucoside (3a) has been isolated in pure form. Studies on red clover and on nine strains of subterranean clover have demonstrated in all cases that the acidic malonate esters account for the predominant proportion of the glycosides.

The germinability of soft seed of a number of strains of subterranean clover

The effect of several seed treatments on germination of 13 strains of subterranean clover (Trifolium subterraneum) seed was examined at two constant temperatures in the laboratory. Tests were conducted on soft seed obtained after scarification of seed sampled on three occasions during the summer and autumn. Germinability varied between strains, but always increased with time after harvest ripeness. Leaching with water promoted some germination in even the most dormant seed. Treatment with carbon dioxide was effective in promoting germination at 20�C, but was less effective than leaching at 30�C. The results suggest that protection against germination by embryo dormancy is likely to be confined to conditions of comparatively high temperatures (>20�C) when associated with summer rains having little or no leaching effect.

Urinary sediments in sheep feeding on oestrogenic clover. I. Preliminary observations on changes in certain urinary constituents

In recent years a series of widespread outbreaks of acute urinary obstruction has occurred in spring in Merino wethers. Animals involved have been grazing oestrogenic strains of subterranean clover at a time when isoflavone concentrations can be expected to be high. Studies have been made on one property on the relationships between these outbreaks, the pasture isoflavone content, and the urinary excretion of phenolic and other constituents by wethers. A trial group of animals was grazed on a dominant sward of the highly oestrogenic Trifolium subterraneum cv. Dinninup during winter and spring. Isoflavone concentrations in the clover reached a peak in early August. However, since the pasture became highly clover-dominant in September and early October the maximum daily intake of isoflavones probably occurred during this period, which also coincided with the occurrence of maximum concentration and maximum daily excretion of total phenols and acid-precipitable material (APM) in the urine. It is suggested that the sediments causing clinical obstructions at this time of the year may be a direct result of increased excretion of phenols. APM showed a highly significant direct relationship with total phenols but its excretion increased at a greater rate than did that of phenols. Urinary calcium excretion also increased at the same time.

Seed production and persistence of Carnamah and other early strains of Trifolium subterraneum in the wheatbelt of Western Australia

Seed production and persistence of the Carnamah, Northam A, Dwalganup, and Geraldton strains of subterranean clover (Trifolium subterraneum L.) were examined in undefoliated swards in the wheatbelt of Western Australia. The early flowering characteristic of Carnamah was not always associated with higher seed yields. Only when there was a well-defined, early finish to the growing season, or when flowering was very much earlier in Carnamah (viz., following an early 'break' to the season), did this strain clearly outyield both Northam A and Geraldton. The seed yield of Dwalganup was generally inferior to that of the other strains. Factors affecting regeneration are discussed. Under low rainfall conditions, poorer germination-regulation of Carnamah, compared with Geraldton and Northam A, would be expected to result in poorer persistence unless offset by higher seed yields in the Carnamah strain.

Physiological and ecological studies on the oestrogenic isoflavones in subterranean clover (T. subterraneum L.) I. Effects of temperature

Two strains of subterranean clover – Yarloop and Mt. Barker – were grown at controlled temperatures ranging from 36/31° to 9/4°C under long-day conditions. Leaf material was analysed for the three isoflavones formononetin, genistein, and biochanin A. In the Mt. Barker strain, the formononetin concentration was low (< 0.2% dry wt.) and varied little with temperature. Otherwise, isoflavone levels generally rose from very low values at 36/31° to a peak at 15/10°, and then decreased again to 9/4°. For both strains the total concentration of the three isoflavones and also the total amount of isoflavones per leaf were highest at 15/10°. This temperature was lower than that at which maximum growth occurred. The data are discussed in relation to evidence on the effects of temperature on the formation of flavonoid (especially anthocyanin) compounds. We conclude that temperature is unlikely to be a major factor in the incidence of "clover disease".