Pa Lane

Multiple traits associated with salt tolerance in lucerne: revealing the underlying cellular mechanisms

Salinity tolerance is a complex trait inferring the orchestrated regulation of a large number of physiological and biochemical processes at various levels of plant structural organisation. It remains to be answered which mechanisms and processes are crucial for salt tolerance in lucerne (Medicago sativa L.). In this study, salinity effects on plant growth characteristics, pigment and nutrient composition, PSII photochemistry, leaf sap osmolality, changes in anatomical and electrophysiological characteristics of leaf mesophyll, and net ion fluxes in roots of several lucerne genotypes were analysed. Salinity levels ranged from 40 to ~200 mm NaCl, and were applied to either 2-month-old plants or to germinating seedlings for a period of between 4 and 12 weeks in a series of hydroponic, pot and field experiments. Overall, the results suggest that different lucerne genotypes employ at least two different mechanisms for salt tolerance. Sodium exclusion appeared to be the mechanism employed by at least one of the tolerant genotypes (Ameristand 801S). This cultivar had the lowest leaf thickness, as well as the lowest concentration of Na+ in the leaf tissue. The other tolerant genotype, L33, had much thicker leaves and almost twice the leaf Na+ concentration of Ameristand. Both cultivars showed much less depolarisation of leaf membrane potential than the sensitive cultivars and, thus, had better K+ retention ability in both root and leaf tissues. The implications of the above measurements for screening lucerne germplasm for salt tolerance are discussed.

Effect of defoliation interval on water-soluble carbohydrate and nitrogen energy reserves, regrowth of leaves and roots, and tiller number of cocksfoot (Dactylis glomerata L.) plants

This study investigated the influence of leaf stage-based defoliation interval on water-soluble carbohydrate and nitrogen energy reserve status, regrowth of leaves and roots, and tiller number of cocksfoot (Dactylis glomerata L.) cv. Kara plants up to 24 days (3.5-leaf stage) following defoliation. Treatments were based on defoliation intervals of 1-, 2-, and 4-leaf stages of regrowth, with treatments terminated when the 1-leaf defoliation interval had been completed 4 times, the 2-leaf interval 2 times, and the 4-leaf interval once. Selected plants were destructively harvested prior to commencement of treatments (H0), immediately following cessation of treatments (H1), and at 5 days (H2), 10 days (H3), and 24 days (H4) following H1. Leaf, root, and tiller dry matter yield were determined at each harvest event, as well as tiller number/plant. Levels of water-soluble carbohydrate and nitrogen reserves in plant stubble and roots were determined at each destructive harvest. Initiation and death of daughter tillers were monitored from H0 to the completion of the study. More frequent defoliation of cocksfoot plants resulted in reduced water-soluble carbohydrate assimilation and therefore leaf, root, and tiller dry matter accumulation during the subsequent recovery period. Defoliation at the 1-leaf stage severely limited the regrowth potential of cocksfoot plants, whereas defoliation at the 2-leaf stage was adequate for plant recovery, but did not maximise regrowth. The results of this study showed that a defoliation interval based on the 4-leaf stage maximises water-soluble carbohydrate reserves, tillering, and leaf and root dry matter yields. The priority sequence for allocation of water-soluble carbohydrate reserves followed the order of leaf growth, root growth, and tillering during the regrowth period. Nitrogen energy reserves were found to play a minor role in the regrowth of cocksfoot plants following defoliation. Additional keyword: leaf stage.

Prospects for three Dorycnium species as forage plants in agricultural systems: a review of their agronomic characteristics

Perennial legumes in the Dorycnium genus may have potential as forage plants that could reduce the seasonality of feed production and improve the sustainability of agricultural systems. However, Dorycnium species are not currently used commercially and little is known about their agronomic characteristics. This review covers the current knowledge on Dorycnium distribution, taxonomy and the agronomic performance of Dorycnium hirsutum, Dorycnium rectum and Dorycnium pentaphyllum, including adaptation, establishment, biomass production, water use, grazing management and nitrogen fixation, along with considerations for animal production. Dorycnium originate from temperate Europe and the Mediterranean basin and may be suitable for other regions with similar climatic conditions. Little data exist on the climatic and edaphic conditions to which Dorycnium species are best adapted. Current evidence suggests that D. hirsutum is widely adapted and might be suitable as a forage plant for acid soils in drier and frost-prone agricultural regions. D. hirsutum also persists well in low rainfall environments (down to 300 mm mean annual rainfall), can produce up to 21 t dry matter(DM)/ha in its first 3 years and, by utilising extra water compared with annual pastures, can reduce water leakage below the root zone, thereby slowing development of dryland salinity. The use of D. rectum would be limited to high rainfall or water-accumulating sites. D. pentaphyllum is a diverse species, yet available material appears to be less productive but has better forage quality than D. hirsutum. Currently, establishment reliability and/or forage digestibility are major limitations of the tested Dorycnium species that restrict their potential role and challenge the feasibility of their future use. Breeding may overcome or minimise these limitations and improved agronomic management might also enhance their usefulness. However, current collected genetic resources of Dorycnium are very limited and targeted collections would be needed to yield better adapted germplasm. Breeding to reduce the high levels of condensed tannins (>13% of DM) to moderate concentrations in Dorycnium might improve forage digestibility and could have positive implications for animal performance and health. Despite the poor digestibility of some Dorycnium species (<60% DM digestibility), these plants may still play a significant role as drought forage to provide feed when other forage sources are in limited supply. Further research is required to quantify the potential of Dorycnium species for commercial release and to determine how these plants should be best managed and integrated into livestock and mixed cropping systems.

Shade performance of a range of turfgrass species improved by trinexapac-ethyl

The increased use of enclosed sports stadiums produces shade conditions that seriously affect the quality of turfgrass surfaces, by encouraging undesirable excess vertical succulent growth. Plant growth regulators offer an opportunity to modify a plant’s growth habit, to enable it to be better adapted to a shady environment. To examine growth response to the plant growth regulator, trinexapac-ethyl, cool-season temperate turfgrasses (Kentucky bluegrass–perennial ryegrass, Poa pratensis L./Lolium perenne L.; creeping bentgrass, Agrostis palustris Huds.; supina bluegrass, Poa supina Schrad.; and tall fescue, Festuca arundinacea Schreb.) and a warm-season species (Bermudagrass, Cynodon dactylon L.) were established in a field experiment. Main treatments were 4 levels of shade (0, 26, 56 or 65% shade), with or without trinexapac-ethyl at a rate of 0.5 kg/ha. A pot experiment measured the vertical shoot growth rates of Kentucky bluegrass–perennial ryegrass and tall fescue under 0, 56 or 65% shade, with and without trinexapac-ethyl. Both experiments were conducted under ambient conditions. Light readings taken in full sunlight, at midday through summer and autumn (major period of assessment), ranged from 1350 to 1950 μmol/m2.s. Trinexapac-ethyl reduced vertical growth of all turfgrass species. This resulted in decreased clipping weights and in clipping material having an increased dry matter percentage (i.e. reduced succulence). The impact of trinexapac-ethyl on sward quality and colour was dependent on shade level, for all species. At 56 and 65% shade, quality and colour improvement was maximised with trinexapac-ethyl application; the magnitude of improvement was dependent on species, with Kentucky bluegrass–perennial ryegrass and bentgrass showing the most benefit. It was concluded that trinexapac-ethyl improved the shade performance of a number of turfgrass species commonly used in high quality turf surfaces. It may offer the potential to reduce costs of managing turf in such an environment.

A comparison of the establishment, productivity and feed quality of four cocksfoot (Dactylis glomerata L.) and four brome (Bromus spp.) cultivars, under leaf stage based defoliation management

A glasshouse study was undertaken to investigate the differences in rate of establishment, productivity, feed quality, and response to defoliation frequency between new and old cultivars within the brome (Bromus spp.) and cocksfoot (Dactylis glomerata L.) genera. Three of the more recent brome (Bareno, Gala, and Exceltas) and cocksfoot (Tekapo, Megatas, and Uplands) cultivars were compared with Matua and Kara, the most widely sown and utilised brome and cocksfoot dairy pasture cultivars, respectively. The improvements resulting from breeding and selection within the cocksfoot genera included faster seedling emergence and tiller production during establishment, higher tiller density once established, lower acid detergent fibre (ADF), higher crude protein (CP), and higher metabolisable energy (ME) concentrations. The newer cocksfoot cultivars had lower leaf and tiller dry matter (DM) yields than Kara, with little variation in ME levels between cultivars. The improvements resulting from breeding and selection within the brome genera, measured in this study, included faster seedling emergence, lower ADF, and higher CP concentrations. The higher fibre levels for Matua did not translate into a lower ME concentration; in fact, the energy content in Matua and Gala was higher than for all remaining cultivars. There were further similarities between Matua and Gala, the high water-soluble carbohydrate levels, leaf, and tiller DM yields of these cultivars, reflecting a strong regrowth response to defoliation. Further research in the field is required to confirm the observed variation within and between cocksfoot and brome cultivars, and to quantify the potential benefits of using the new v. the original cultivars.

Selection and evaluation of root nodule bacteria for Dorycnium spp

Dorycnium spp. are perennial legumes that have the ability to produce a source of forage in low fertility soils under low rainfall conditions. The inoculation of Dorycnium spp. is currently with the commercial Lotus corniculatus inoculant SU343, which until now had not been trialed against a range of alternative inoculants for Dorycnium spp. A glasshouse trial in sterile sand culture was conducted with 3 species of Dorycnium spp. along with 6 important pasture legumes to evaluate nitrogen-fixing performance, and host and rhizobia interactions. Several inoculants were selected from this trial to undergo evaluation under Tasmanian field conditions. The dry matter production of Dorycnium spp. in the glasshouse and field indicated that SU343 is a suitable inoculant for this genus. A Tasmanian isolate (WSM2338) was identified as a complimentary strain for the inoculation of Dorycnium spp., however, negative interactions with important pasture legumes require further investigation.

Occurrence and severity of the weeds Anthriscus caucalis and Torilis nodosa in pyrethrum

Pyrethrum [Tanacetum cinerariifolium (Trevis.) Sch.Bip.] is a short-lived, perennial horticultural crop grown for the production of pyrethrins. Weed management in pyrethrum is heavily reliant on chemical use and has unintentionally selected for a range of species. One of the major concerns to the pyrethrum industry is the presence of Apiaceae species, Anthriscus caucalis M. Bieb and Torilis nodosa (L.) Gaertn. Increased occurrence and severity of infestation of these species in pyrethrum is a threat to the industry through reduced crop yields and increased costs for their control. To determine the severity of this threat, pyrethrum crops were surveyed for the presence and level of infestation of A. caucalis and T. nodosa over 2 years. More than 30% of all pyrethrum crops had either 1 or both species present, with A. caucalis the more prevalent of the 2 species. Although the level of infestation was generally low, 23 pyrethrum crops had a severe or very severe infestation of the species in 2001. The severity of infestation was generally low, although older crops were found to have a higher level of infestation than newly established crops. All pyrethrum crops, which had undergone 4 annual harvests, were found to have Apiaceae weeds present. This work has documented the severity of occurrence of these species and highlighted the need to develop strategic control procedures to reduce their immediate impact and potential threat.

Gene Expression Profiles of Aralkylamine N-Acetyltransferase, B-cell Translocation Gene-2 and Fatty Acid Synthase in Pasture-based Primiparous Holstein-Friesian Dairy Cows Supplemented with Crude Degummed Canola Oil

The effect of oil-rich supplements on the expression of genes involved in lipogenesis and reproduction in pasturebased dairy cows is currently unknown, or at best, scanty and limited to impacts on cow liveweight, body condition score, milk composition, fatty acid and plasma metabolite profiles only. This research investigated the gene expression patterns of Aralkylamine N-acetyltransferase (AANAT), B-cell translocation gene-2 (BTG2) and Fatty Acid Synthase (FASN) genes in response to incremental levels of dietary crude degummed canola oil (CDCO). We tested the hypothesis that the relative mRNA abundance and gene expression profiles of AANAT, BTG2 and FASN in primiparous Holstein-Friesian cows will be up-regulated in response to post-partum dietary supplementation with CDCO in a typical pasture-based dairy production system. Thus, the primary objective of this study was to investigate the expression of AANAT, BTG2 and FASN genes in response to incremental levels of CDCO. A random allocation of primiparous Holstein-Friesian dairy cows into four treatment groups comprising wheat-based pelleted with no supplemental CDCO (control), or with CDCO added at 25 ml kg-1 DM (low), 35 ml kg-1 DM (medium) and 50 ml kg-1 DM (high) was utilized in a ten-week experimental feeding trial including two weeks of adjustment. Both level of supplementation and their interaction with duration were significant sources of variation (P 0.05). The high (0.67 fold), medium (0.87 fold) and low (0.56 fold) treatments had suppressed BTG2 expressions compared to the control (1.0 fold) group. The low expression of BTG2 might be important when the reproductive system of cows is recovering from the effect of gestation and new cell growth is required.

Leaf growth and senescence rates of three pasture grasses and wheat

Abstract. A glasshouse study was conducted under ideal conditions to determine leaf appearance, elongation, and senescence rates along with life span and leaf length characteristics of four grass species: wheat (Triticum aestivum L.), brown back wallaby grass (Rytidosperma duttonianum (Cashmore) Connor and Edgar), phalaris (Phalaris aquatica L.), and annual ryegrass (Lolium rigidum Gaud.). This study provided a comprehensive characterisation of leaf turnover rates for the entire life cycle of these grasses, some of which are poorly characterised. Importantly, leaf senescence rate has been captured in the same conditions as the other leaf rates of the life cycle. Leaf position proved to be a significant explanatory variable in each of the leaf turnover rates. The relationships between leaf position and the components of leaf turnover were most commonly represented by non-linear models. Further studies may be necessary to validate these statistical models to field situations. However, this information will be useful to calibrate the senescence algorithms of plant growth models in agricultural decision support tools, which may then be applied to simulation studies including the assessment of grass curing for planning activities such as resource allocation, wildfire suppression, and execution of prescribed burning programs by fire management agencies.

Evaluation of a Nutrition Model in Predicting Performance of Vietnamese Cattle

The objective of this study was to evaluate the predictions of dry matter intake (DM) and average daily gain (ADG) of Vietnamese Yellow (Vang) purebred and crossbred (Vang with Red Sindhi or Brahman) bulls fed under Vietnamese conditions using two levels of solution (1 and 2) of the large ruminant nutrition system (LRNS) model. Animal information and feed chemical characterization were obtained from five studies. The initial mean body weight (BW) of the animals was 186, with standard deviation ±33.2 kg. Animals were fed ad libitum commonly available feedstuffs, including cassava powder, corn grain, Napier grass, rice straw and bran, and minerals and vitamins, for 50 to 80 d. Adequacy of the predictions was assessed with the Model Evaluation System using the root of mean square error of prediction (RMSEP), accuracy (Cb), coefficient of determination (r2), and mean bias (MB). When all treatment means were used, both levels of solution predicted DMI similarly with low precision (r2 of 0.389 and 0.45 for level 1 and 2, respectively) and medium accuracy (Cb of 0.827 and 0.859, respectively). The LRNS clearly over-predicted the intake of one study. When this study was removed from the comparison, the precision and accuracy considerably increased for the level 1 solution. Metabolisable protein was limiting ADG for more than 68% of the treatment averages. Both levels differed regarding precision and accuracy. While level 1 solution had the least MB compared with level 2 (0.058 and 0.159 kg/d, respectively), the precision was greater for level 2 than level 1 (0.89 and 0.70, respectively). The accuracy (Cb) was similar between level 1 and level 2 (p = 0.8997; 0.977 and 0.871, respectively). The RMSEP indicated that both levels were on average under- or over-predicted by about 190 g/d, suggesting that even though the accuracy (Cb) was greater for level 1 compared to level 2, both levels are likely to wrongly predict ADG by the same amount. Our analyses indicated that the level 1 solution can predict DMI reasonably well for this type of animal, but it was not entirely clear if animals consumed at their voluntary intake and/or if the roughness of the diet decreased DMI. A deficit of ruminally-undegradable protein and/or a lack of microbial protein may have limited the performance of these animals. Based on these evaluations, the LRNS level 1 solution may be an alternative to predict animal performance when, under specific circumstances, the fractional degradation rates of the carbohydrate and protein fractions are not known.