White Clover Cultivars Research Articles

Nodule occupancy of effective rhizobia vary between historical and modern cultivars of white clover

ABSTRACT The ability of plants to select effective symbiotic partners is crucial for optimum plant growth. In New Zealand, breeding programmes for white clover (Trifolium repens) have made selections largely based on above-ground characteristics, with little direct attention given to the ability of cultivars to form effective below-ground associations. The ability of three pairs of historical (1930s–1950s), and modern (2000s) cultivars of white clover, to form associations with effective strains of Rhizobium leguminosarum (rhizobia) from a mixture of strains was tested in vitro. First, the efficacy of six individual strains of rhizobia was ranked against all six clover cultivars with shoot biomass used as a direct measure of symbiotic effectiveness for each strain × cultivar combination. Next, each cultivar was inoculated with a mixture of all rhizobia strains at the same cell concentration to examine the identity and frequency of strains found on each host. There was a positive relationship between nodule occupancy and strain effectiveness for historical but not modern cultivars. Cultivars Grasslands Huia and Louisiana (both historical) had nodule occupancy increase with strain effectiveness. This study provides some evidence that historical cultivars may be better able to form associations with effective strains of rhizobia compared with modern cultivars.

Lipid remodelling and the conversion of lipids into sugars associated with tolerance to cadmium toxicity during white clover seed germination.

Cadmium (Cd) is a leading environmental issue worldwide. The current study was conducted to investigate Cd tolerance of 10 commercial white clover (Trifolium repens) cultivars during seed germination and to further explore differences in lipid remodelling, glycometabolism, and the conversion of lipids into sugars contributing to Cd tolerance in the early phase of seedling establishment as well as the accumulation of Cd in seedlings and mature plants. The results show that Cd stress significantly reduced seed germination of 10 cultivars. Compared to Cd-sensitive Sulky, Cd-tolerant Pixie accelerated amylolysis to produce more glucose, fructose, and sucrose by maintaining higher amylase and sucrase activities under Cd stress. Pixie maintained higher contents of various lipids, higher DGDG/MGDG ratio, and lower unsaturation levels of lipids, which could be beneficial to membrane stability and integrity as well as signal transduction in cells after being subjected to Cd stress. In addition, Pixie upregulated expression levels of key genes (TrACX1, TrACX4, TrSDP6, and TrPCK1) involved in the conversion of lipids into sugars for early seedling establishment under Cd stress. These findings indicate that lipid remodelling, enhanced glycometabolism, and accelerated conversion of lipids into sugars are important adaptive strategies for white clover seed germination and subsequent seedling establishment under Cd stress. In addition, Pixie not only accumulated more Cd in seedlings and mature plants than Sulky but also had significantly better growth and phytoremediation efficiency under Cd stress. Pixie could be used as a suitable and critical germplasm for the rehabilitation and re-establishment of Cd-contaminated areas.

Comparative Study on the Morpho-Physiological Responses of White Clover Cultivars with Different Leaf Types to Water Deficiency

White clover (Trifolium repens L.) is one of the legume herbages with high feed quality, but it is sensitive to water deficiency. The objectives of this study were to compare morpho-physiological responses to drought stress and post-drought recovery in four-leafed white clover cultivars. Under well-watered conditions, drought stress (3 d, 6 d, 9 d and 12 d), and rehydration, the relative water content (RWC), membrane lipid permeability, osmoregulatory substances, photosynthetic characteristics and stomatal features of Chinese native Longping No.1 (LP, small-leafed) and three introduced cultivars, namely Pudi (PD, small-leafed), Rivendel (RD, medium-leafed) and Koala (KL, large-leafed), were evaluated. Results showed that small-leafed white clover maintained higher RWC and better membrane stability and osmotic regulation with increased drought intensities, compared to the medium-leafed and large-leafed cultivars. Following rewatering, small-leafed white clover recovered more rapidly with all of the parameters than the other cultivars. The increase of drought stress intensity led to the decline of net photosynthetic rate (Pn), transpiration rate (Tr) and stomatal conductance (Cs). However, the decreased range of Pn, Tr and Cs in the small-leafed white clover was significantly smaller than that in the medium-leafed and large-leafed white clovers. Meanwhile, the small-leafed white clover showed a smaller size and higher density of stoma either under normal or drought conditions than the intermediate- and large-leafed cultivars. Taken together, the results indicated that the adaptability of small-leafed white clover to drought stresses and post-drought recovery was better than that of medium-leafed and large-leafed white clovers. The study will provide better insights into the mechanism of drought response and recovery potential in different white clover cultivars.

Phosphorus responses of Trifolium pallescens and T. occidentale, the progenitors of white clover (T. repens)

Context Rock phosphate reserves are decreasing, and requirements to mitigate environmental impacts of farming soils with excess phosphorus (P) are increasing. Aims White clover is an allotetraploid hybrid between Trifolium pallescens and T. occidentale. Understanding the P response characteristics of these progenitor species will allow selection of germplasm for development of synthetic white clovers with improved phosphorus-use efficiency (PUE). Methods Shoot and root weights and P nutrition characteristics were compared for three Trifolium pallescens, six T. occidentale accessions, and a white clover cultivar in a glasshouse experiment using a low P soil amended with five rates of P. Key results White clover had the highest and most P responsive shoot and root dry weights (DW), and T. pallescens was least responsive to P. In the highest P treatment, T. pallescens had the highest shoot and root %P and the lowest shoot DW:total plant P ratio. There was significant variation among progenitor accessions. Spanish accessions of T. occidentale had comparable shoot DW to white clover and higher PUE. Traits of T. pallescens indicated strong adaptation to low P but low productivity, while traits of T. occidentale were more aligned with the white clover cultivar. Conclusions The substantial variation in P nutrition characteristics within the progenitor species of white clover could be exploited in breeding programs. Implications Comparing the P responses of a wider range of progenitor accessions could inform breeding to improve white clover’s low soil P tolerance through development of synthetic white clovers.

Screening and field evaluation of white clover rhizobia for New Zealand pastures

Context Biological nitrogen (N) fixation through the rhizobia–legume symbiosis is a sustainable and cost-effective source of N for agriculture. In New Zealand (NZ), white clover (Trifolium repens) is a key component of pastures and rhizobial inoculation of clover is widely used. The current commercial inoculant for white clover, TA1, was isolated in Australia in the 1950s and may not be the best partner for modern white clover cultivars. Aims To identify Rhizobium leguminosarum bv. trifolii (Rlt) isolates suitable for use in NZ pastures. Methods The symbiotic potential of >230 isolates collected from throughout NZ was evaluated in plant bioassays. Selected isolates were further evaluated in pot and field trials. Key results Approximately 40% of NZ isolates supported better clover growth than TA1 under N-limited conditions in vitro. Of 24 Rlt isolates evaluated in a glasshouse trial, five produced significantly higher clover biomass than TA1. Three (S11N9, S20N7, S4N6) of nine isolates evaluated in two field trials in 2018–2019 significantly increased clover growth (12–38%) compared with paired uninoculated clover at several harvests, whereas inoculation with TA1 did not improve yield. In a third trial in 2020, S11N9 and S20N7 increased clover growth compared with the uninoculated control at two of three harvests; S4N6 performed better than TA1 at one harvest. When tested with four white clover cultivars, five Rlt isolates had higher symbiotic potential than TA1. Conclusions Inoculating white clover would be beneficial if improved inoculant isolates were available. Implications We recommend some NZ Rlt isolates could be developed into commercial inoculants to improve white clover performance in NZ.

Integrative analysis of the metabolome and transcriptome provides insights into the mechanisms of anthocyanins and proanthocyanidins biosynthesis in Trifolium repens

Anthocyanin and proanthocyanidin (PA) are plant natural products beneficial to human and livestock health. In particular, the legume forage with proper PA contents can prevent lethal pasture bloat in ruminant animals. To study the mechanism underlying anthocyanin and PA biosynthesis in legume forages, comparative transcriptomics and metabolomics analyses were performed with ‘Purple’ and ‘Haifa’ white clovers. Metabolic analyses revealed that pelargonidin may be the most important source of color in ‘Purple’. Cyanidin-3-O-(6''-O-p-coumaroyl)-glucoside, petunidin-3-O-(6''-O-p-coumaroyl)-rutinoside, and delphinidin-3-O-rutinoside-7-O-glucoside might contribute to PA biosynthesis. Additionally, 67 differentially expressed genes in anthocyanin and PA biosynthetic pathways were discovered between ‘Purple’ and ‘Haifa’. Among them, DFR (dihydroflavonol-4-reductase), LDOX/ANS (leucoanthocyanidin oxygenase/anthocyanidin synthase), (leucoanthocyanidin reductase), ANR (anthocyanidin reductase), and UFGT (UDPglucose:flavonoid-3-O-glucosyltransferase) may be key determinants of the differences in anthocyanin and PA biosynthesis. Finally, A hypothetical model of gene expression regulating the synthesis of PAs and anthocyanins in white clover was proposed, which could provide a molecular genetic basis for future candidate genes validation and breeding high-PA white clover cultivars.

The hunt for the “holy grail”: Condensed tannins in the perennial forage legume white clover (Trifolium repens L.)

AbstractForage legumes such as white and red clover improve the nutritional quality of grazed pasture but can cause bloat. Their rapid fermentation in the rumen also contributes to environmental issues through higher methane emissions and urinary nitrogen losses. Condensed tannins are known to reduce urinary nitrogen and methane production from grazing animals, reduce bloat, reduce internal parasite burden, and improve animal productivity. Several forage legumes including birdsfoot trefoil and sainfoin do have good levels of condensed tannins but unfortunately these species fail to persist in intensively grazed pasture systems. Conventional breeding approaches including mutagenesis and phenotypic selection have failed to deliver condensed tannins in legumes, such as white clover, red clover or lucerne, that do persist under grazing. A recent advance using a molecular biology approach has identified a transcription factor or master switch that can 'turn on' the condensed tannin pathway present in white clover allowing biologically significant levels of condensed tannin expression in leaf tissue. In vitro tests have demonstrated that the condensed tannins produced in white clover leaves can bind protein at a pH 6.5, as found in the rumen, and then release them at pH 2.5, the pH in the abomasum, before entering the small intestine for amino acid absorption. Additional tests have demonstrated that these condensed tannins can reduce methane production by up to 15.7% in the first 6 h of incubation. The journey to this point, and the challenges ahead to deliver white clover cultivars with condensed tannin expression, is described.

Enhanced Adaptability to Limited Water Supply Regulated by Diethyl Aminoethyl Hexanoate (DA-6) Associated With Lipidomic Reprogramming in Two White Clover Genotypes.

Membrane lipid reprogramming is one of the most important adaptive strategies in plant species under unfavorable environmental circumstances. Therefore, the present experiment was conducted to elucidate the effect of diethyl aminoethyl hexanoate (DA-6), a novel synthetic plant growth regulator, on oxidative damage, photosynthetic performance, changes in lipidomic profile, and unsaturation index of lipids in two white clover (Trifolium repens) cultivars (drought-sensitive “Ladino” and drought-resistant “Riverdel”) under PEG-6000-induced water-deficit stress. Results revealed that water-deficit stress significantly enhanced oxidative damage and decreased photosynthetic functions in both cultivars. However, the damage was less in Riverdel. In addition, water-deficit stress significantly decreased the relative content of monogalactocyl-diacylglycerols (MGDG), sulfoquinovosyl-diacylglycerols (SQDG), phosphatidic acisd (PA), phosphatidyl-ethanolamines (PE), phosphatidyl-glycerols (PG), phosphatidyl-serines (PS), ceramides (Cer), hexosylmonoceramides (Hex1Cer), sphingomyelins (SM), and sphingosines (Sph) in both cultivars, but a more pronounced decline was observed in Ladino. Exogenous application of DA-6 significantly increased the relative content of digalactocyl-diacylglycerols (DGDG), monogalactocyl-diacylglycerolsabstra (MGDG), sulfoquinovosyl-diacylglycerols (SQDG), phosphatidic acids (PA), phosphatidyl-ethanolamines (PE), phosphatidyl-glycerols (PG), phosphatidyl-inositols (PI), phosphatidyl-serines (PS), ceramides (Cer), hexosylmonoceramides (Hex1Cer), neutral glycosphingolipids (CerG2GNAc1), and sphingosines (Sph) in the two cultivars under water-deficit stress. DA-6-treated Riverdel exhibited a significantly higher DGDG:MGDG ratio and relative content of sphingomyelins (SM) than untreated plants in response to water deficiency. Furthermore, the DA-6-pretreated plants increased the unsaturation index of phosphatidic acids (PA) and phosphatidylinositols (PI) in Ladino, ceramides (Cer) and hexosylmonoceramides (Hex1Cer) in Riverdel, and sulfoquinovosyl-diacylglycerols (SQDG) in both cultivars under water stress. These results suggested that DA-6 regulated drought resistance in white clover could be associated with increased lipid content and reprogramming, higher DGDG:MGDG ratio, and improved unsaturation index of lipids, contributing to enhanced membrane stability, integrity, fluidity, and downstream signaling transduction.

R2R3-MYB gene family: Genome-wide identification provides insight to improve the content of proanthocyanidins in Trifolium repens

The R2R3-MYB family is one of largest transcription factor families in plants playing significant roles in regulating anthocyanin and proanthocyanidin biosynthesis. Proanthocyanidins are one of major objectives to improve the quality of white clover (Trifolium repens L.), which have a beneficial effect on ruminant to prevent the lethal pasture bloat. A total of 133 TrR2R3-MYB genes were identified and distributed on all 16 chromosomes based on the whole genome information of white clover. Also, by exploring the gene structure, motifs and duplication events of TrR2R3-MYBs, as well as the evolutionary relationship with TrR2R3-MYB genes of other species, 10 TrR2R3-MYB genes with the potential to regulate the anthocyanins and proanthocyanidins biosynthesis were screened. These TrR2R3-MYB genes responded significantly to low temperature in white clover. In addition, they have different expression patterns in leaves, petioles and inflorescences of white clover. Importantly, TrMYB116 and TrMYB118 may positively regulate anthocyanin accumulation and low temperature response in white clover. TrMYB118 may also be associated with anthocyanin pigmentation pattern in Purple leaves. This study provides a basis for verifying the function of TrR2R3-MYB and breeding white clover cultivars with high proanthocyanidins.

A Retrospective Analysis of White Clover (Trifolium repens L.) Content Fluctuation in Perennial Ryegrass (Lolium perenne L.) Swards under 4 Years of Intensive Rotational Dairy Grazing

The objective of this study was to examine fluctuations in white clover (Trifolium repens L.) content in perennial ryegrass (Lolium perenne L.) swards within a high nitrogen (250 kg N/ha) input grazing dairy system. The data came from a larger, overall system experiment within which all management and growing condition variables were categorised each year for the 40 paddocks that contained perennial ryegrass-white clover swards, over four growing years. Within that study, eight perennial ryegrass cultivars were examined, each sown individually with two white clover cultivars in a 50:50 mix of ‘Chieftain’ and ‘Crusader’. To determine management associations and meteorological patterns with white clover content and rate/direction of change, separate generalised linear models were used to analyse each individual management or meteorological variable. Paddocks with high white clover contents were associated with lower pre- and post-grazing sward heights, lower pasture cover over the winter period and shorter over-winter period. Perennial ryegrass cultivars with lower pre- and post-grazing height, lower pre-grazing pasture mass and pasture yield removed, all retained more white clover in their swards. Soil fertility remained a key factor that affected white clover persistence influencing the degree of responses in all treatments, particularly soil phosphorus (P) levels. Beyond this, higher white clover contents and lower rates of white clover decline were associated with paddocks that received lower rainfall, had higher soil moisture deficits and received more radiation into the base of the sward, particularly around the time of grazing.

Response of white clover cultivars to sheep and beef cattle grazing management across three pastoral environments in New Zealand.

White clover (Trifolium repens L.) is the main legume component in temperate perennial pasture swards in New Zealand. Developing broadly adapted cultivars is an important objective in white clover breeding programs. Field trials across years, seasons, locations and grazing environments, help breeders select superior material, and assess the merit of new cultivars available to farmers. This paper is based on results from analysis of data from field trials across three locations in New Zealand: Kerikeri (cattle grazed), Palmerston North (cattle grazed) and Lincoln (sheep grazed), evaluating 44 experimental varieties and 16 cultivars for seasonal growth and leaf size. We report on performance of the 16 cultivars across the three locations.
 Significant genotype-by-environment interactions were estimated for seasonal growth and leaf size. The importance of conducting multi-location and year evaluation trials under cattle and sheep grazing management methods (rotational/set stocking) was demonstrated. Among the 16 cultivars, Legacy showed above average performance across all 3 locations. Hilltop when compared among similar leaf size material, showed above average seasonal growth across years under rotational sheep grazing management during the first 4 years of the trial at Lincoln. Hilltop also showed above average seasonal growth under set socking with sheep in years 5 and 6 at Lincoln.

Morpho‐physiological changes induced by soil environment modulate the compatibility of perennial ryegrass and white clover cultivars

AbstractThe effect of soil environment on cultivars compatibility was evaluated in a cutting field experiment during two growing seasons. A factorial combination of four perennial ryegrass (Lolium perenne L.; PR) and three white clover (Trifolium repens L.; WC) cultivars were grown on deep (DSS) and shallow (SSS) soils under irrigated conditions. Measurements included herbage accumulation (HA), root attributes, leaf chlorophyll content, and interception of photosynthetic radiation. The PR–WC compatibility was affected by soil environment. In both soil sites and growing seasons, the WC + PR herbage accumulations were similar but with different PR and WC partial accumulation. In DSS, the partial PR HA was 22% less than that observed in SSS; the partial WC HA was almost twice in DSS relative to SSS. In SSS, the WC stolon growing point numbers, stolon length, and stolon biomass increased 60, 88, and 94% relative to DSS, respectively. In the same way, the mixed sward increased root biomass and root length density, which was considered as a mechanism for improving plant resources capture from the soil. At cultivar level, the PR–WC compatibility was affected mainly by WC cultivar, and the effect of PR cultivar was fairly weak. The medium‐leaved WC cultivar ‘Will’ showed the greatest compatibility with PR, particularly with cultivar ‘Bealey’. These results are valuable when designing new management strategies for mixed sward production in marginal environments. Modern cultivars of PR have capacity for adapting to marginal environments; however, it is necessary to improve the competitive ability of WC to capture soil resources under marginal soil conditions.

Transpiration Rate of White Clover (Trifolium repens L.) Cultivars in Drying Soil.

Determining the performance of white clover cultivars under drought conditions is critical in dry climates. However, comparing the differences in cultivar performance requires equivalent soil water content for all plants, to reduce the water deficit threshold eliciting stomatal closure. In this study, the objective was to compare the rate of stomatal closure in eighty white clover cultivars in response to soil drying. Two glasshouse experiments were conducted, and the daily transpiration rate was measured by weighing each pot. The transpiration rate of the drought-stressed plants were normalized against the control plants to minimize effects from transpiration fluctuations and was recorded as the normalized transpiration rate (NTR). The daily soil water content was expressed as the fraction of transpirable soil water (FTSW). The FTSW threshold (FTSWc) was estimated after which the NTR decreases linearly. The FTSWc marks the critical point where the stomata start to close, and transpiration decreases linearly. The significant difference (p < 0.05) between the 10 cultivars with the highest and lowest FTSWc demonstrates the cultivars would perform better in short- or long-term droughts.

Cross-host compatibility of commercial rhizobial strains for new and existing pasture legume cultivars in south-eastern Australia

Perennial legumes have potential to increase pasture productivity in the high rainfall zone (600–850 mm) of south-eastern Australia through their ability to use summer rainfall and fix nitrogen (N2). Various perennial legumes are being evaluated for this environment; however, little information exists on legume–rhizobia cross-host compatibility and its consequences for biological N2 fixation. This is especially important when legumes are sown into fields with a background of competitive rhizobia such as WSM1325 or sown as a pasture mix with different host–symbiont pairs. We studied the effectiveness and cross-host compatibility of five commercial rhizobial strains for a range of pasture legumes (nine species, 18 cultivars) under controlled environment conditions, and further evaluated nodule occupancy and competitiveness of a newly established pasture (13 species, 20 cultivars) in the field, by determining nodulation and production (biomass and N2 fixation). Three of the commercial inoculant strains formed root nodules with multiple legume species; commonly however, less N2 was fixed in cases where the inoculant was not the recommended strain for the legume species. Within a legume species, cultivars could differ in their ability to form effective root nodules with multiple rhizobial strains. White clover cvv. Trophy, Haifa and Storm, strawberry clover cv. Palestine, and Talish clover cv. Permatas formed effective nodules with both TA1 and WSM1325 rhizobial strains. White clover cultivars that could not form an effective symbiosis with the common background strain WSM1325 fixed less N2. The white clover × Caucasian clover hybrid formed effective symbiosis with strain TA1 but not with other commercial strains. Some species such as birdsfoot trefoil, Talish clover, sulfur clover and tetraploid Caucasian clover formed ineffective symbiosis in the field. Until resolved, this will likely inhibit their further development as pasture plants for similar permanent pasture environments.

Relative performance of white clover (

Assessment of the relative performance of white clover (Trifolium repens L.) cultivars, using multi-year and multi-location seasonal growth trials, is key to identification of material with specific and broad adaptation. This paper is based on a multi-year and multi-location study of 56 white clover entries comprising 14 commercial cultivars and 42 experimental synthetic lines evaluated for seasonal growth under rotational grazing across four locations in New Zealand over 4 years. The four locations (and animals grazing) were: Kerikeri (beef cattle), Aorangi (beef cattle), Ruakura (dairy cattle), Lincoln (sheep). Significant (P &lt; 0.05) genotypic variation among the 56 entries, and genotype × year, genotype × location and genotype × season interactions, were estimated. We were able to identify cultivars and experimental synthetics with specific and broad adaptation to the three grazing management types. Cvv. AberDance, Apex, Demand, Prestige, Quartz and Riesling, with leaf size ranging from small to medium–large, showed highly above-average performance under sheep grazing. Synthetic lines 15 and 45 also had highly above-average performance under sheep grazing. Cvv. Legacy and Kopu II showed above-average performance under cattle and dairy grazing. Synthetics 15, 48, 49, 44, 22 and 18 and cv. Quartz had above-average performance under all three grazing managements. Synthetics 27, 33 and 38 had highly above-average performance across all three grazing managements and were superior to all 14 cultivars evaluated. Several of these superior synthetics are being tested across multiple grazing environments. Among the 14 cultivars evaluated, Legacy and Quartz showed superior seasonal growth performance across the three grazing managements. Quartz is being evaluated in several on-farm trials across temperate regions of the world.

Fingerprint identification of white clover cultivars based on SSR molecular markers.

White clover (Trifolium repens L.) is an important perennial legume forage with high productivity and quality. To strengthen the basic research on the genetic characteristics, fingerprint identification and adaptability of white clover germplasm resources, Simple sequence repeat (SSR) molecular markers were applied to 10 white clover cultivars to assess the genetic diversity and related lines of white clover at the molecular level in order to lay a theoretical foundation for the selection of high-quality seeds and cultivars of white clover. A total of 120 different bands were amplified by 29 pairs of SSR primers with good polymorphism, of which 103 (89.5%) were polymorphic. Meanwhile, the PIC of each primer was 0.181-0.588, with an average of 0.329. Analysis of molecular variance revealed that 57% of the genetic variation occurred within cultivars and 43% occurred among cultivars. The results of cluster analysis and the principal coordinate analysis revealed that the parental relationships of the 10 cultivars, with the 'Purple' cultivar very distantly related to the other 9 cultivars and the closest parental relationship between 'Ladino' and 'Sulky'. The fingerprints constructed by three representative primers (gtrs679, gtrs319, and gtrs678) have a strong identification ability. In summary, the SSR markers had good polymorphism and could be used for DNA fingerprint analysis of white clover cultivars.

Seasonal and Diurnal Variation in Water-Soluble Carbohydrate Concentrations of Repeatedly Defoliated Red and White Clovers in Central Kentucky

Nonstructural carbohydrates of pasture plants, comprising water-soluble carbohydrates (WSCs) and starch, may contribute to excessive consumption of rapidly fermentable carbohydrates by grazing horses. Seasonal and diurnal variation in WSCs were studied in red (Trifolium pratense L.) and white clovers (Trifolium repens L.) subjected to a typical management regime of rotationally grazed horse pastures. Two red and two white clover cultivars from monoculture plots were harvested after 4 weeks of growth from April to October of 2015, in the morning and afternoon of each harvest date. Water-soluble carbohydrates were quantified for each harvest, and starch was quantified for two harvests. Mean monthly WSC concentrations ranged from 80 to 99 mg/g (freeze-dried weight basis), whereas mean starch concentrations were 31 and 40 mg/g. In September, white clover had 14% more WSCs than red clover (P < .0001). Water-soluble carbohydrate concentrations were 10% higher in the afternoon than in the morning (P < .0001). Starch concentrations were 290% higher in the afternoon than in the morning (P < .0001), and nonstructural carbohydrate concentrations in the afternoon averaged 150 mg/g. Further studies are needed to determine whether the mixed grass-legume pastures of central Kentucky accumulate enough nonstructural carbohydrates to present risk factors for equine metabolic or digestive dysfunction.

Symbiosis between Rhizobium leguminosarum bv. trifolii strain TA1 and a white clover cultivar benefits clover tolerance to cadmium toxicity

ABSTRACT New Zealand pastoral productivity relies heavily on biological nitrogen (N) fixation from rhizobia bacteria. Cadmium (Cd), present in pasture soils as an impurity in phosphate fertilisers, may have toxic effects on both plant growth and rhizobia activity. Effects of Cd on growth of seedlings of a white clover cultivar ‘Grasslands Tribute’, in the absence and presence of the N2-fixing Rhizobium leguminosarum bv. trifolii strain TA1, were assessed in vermiculite microcosm assays. The lowest observable effect concentrations resulting in significantly lower white clover shoot weights than those grown without Cd were 0.07 mg Cd kg−1 (measured as Ca(NO3)2-extractable Cd, Cdextractable) in the absence of Rhizobium, and 2.33 mg Cdextractable kg−1 for Rhizobium-inoculated seedlings. Shoot N content was unaffected in white clover exposed to <5 mg Cdextractable kg−1. The results indicate symbiosis with Rhizobium strain TA1 conferred tolerance to white clover ‘Grasslands Tribute’ against Cd toxicity, and that this symbiosis is unlikely to be adversely affected by Cd concentrations reported (<0.003 mg Cdextractable kg−1) in New Zealand pasture soils.

Thiamin-induced variations in oxidative defense processes in white clover ( Trifolium repens L.) under water deficit stress

Vitamins are regarded as vital growth substances. They act as cofactors of various key enzymes involved in metabolism and also have vital influence on metabolic activities of plants. They are believed to play a significant role in plants against abiotic stresses, particularly during water stress. The current experiment was conducted to evaluate the role of exogenously applied thiamin on two white clover cultivars, Super Late Fsd and Layalpur Late, at varying [100% (control), 80%, and 60% field capacities] water regimes. A significant suppression was noted in plant biomass, plant height, chlorophyll a and b contents, total soluble proteins, and shoot and root P, Ca 2+ , and K + contents particularly at 60% field capacity in both cultivars. Drought stress had no significant effect on phenolic contents, but MDA concentration was increased in white clover cultivar Layalpur Late at both 80% and 60% drought levels. However, in Super Late Fsd, it was increased at 80% and decreased at 60% field capacity. Drought stress significantly enhanced levels/activities of ascorbic acid and antioxidant enzymes (CAT, SOD, and POD). Foliar spray of 50 mM thiamin improved the shoot and root fresh weights and shoot dry weight. Varying levels of thiamin were found significantly effective for shoot length, root length, and photosynthetic pigments (chlorophyll a and b ). However, no considerable change was observed in ascorbic acid, total soluble proteins, and activities of antioxidants (SOD, CAT, and POD) due to exogenous spray of thiamin on two white clover cultivars. Of the two white clover cultivars, Super Late Fsd was better in shoot and root P and Layalpur Late in root dry weight and root length. Overall, 100 mM of thiamin was found effective in improving growth of both white clover cultivars, which can be attributed to thiamin-induced improvement in photosynthetic pigments and phenolic contents.

First record of White clover cryptic virus-2 in New Zealand

White clover cryptic virus-2 is recorded for the first time in New Zealand in three commercial cultivars of white clover: Grasslands Huia, Grasslands Kopu II and Grasslands Sustain. An RT-PCR assay was used to amplify and sequence a ~590 bp fragment of the coat protein gene.