Differential metabolic responses of perennial grass Cynodon transvaalensis×Cynodon dactylon (C₄) and Poa Pratensis (C₃) to heat stress

Differential metabolic responses to heat stress may be associated with variations in heat tolerance between cool‐season (C₃) and warm‐season (C₄) perennial grass species. The main objective of this study was to identify metabolites associated with differential heat tolerance between C₄ bermudagrass and C₃ Kentucky bluegrass by performing metabolite profile analysis using gas chromatography‐mass spectrometry. Plants of Kentucky bluegrass (Poa Pratensis‘Midnight’) and hybrid bermudagrass (Cynodon transvaalensis×Cynodon dactylon‘Tifdwarf’) were grown under optimum temperature conditions (20/15°C for Kentucky bluegrass and 30/25°C for bermudagrass) or heat stress (35/30°C for Kentucky bluegrass and 45/40°C for bermudagrass). Physiological responses to heat stress were evaluated by visual rating of grass quality, measuring photochemical efficiency (variable fluorescence to maximal fluorescence) and electrolyte leakage. All of these parameters indicated that bermudagrass exhibited better heat tolerance than Kentucky bluegrass. The metabolite analysis of leaf polar extracts revealed 36 heat‐responsive metabolites identified in both grass species, mainly consisting of organic acids, amino acids, sugars and sugar alcohols. Most metabolites showed higher accumulation in bermudagrass compared with Kentucky bluegrass, especially following long‐term (18 days) heat stress. The differentially accumulated metabolites included seven sugars (sucrose, fructose, galactose, floridoside, melibiose, maltose and xylose), a sugar alcohol (inositol), six organic acids (malic acid, citric acid, threonic acid, galacturonic acid, isocitric acid and methyl malonic acid) and nine amino acids (Asn, Ala, Val, Thr, γ‐Aminobutyric acid, IIe, Gly, Lys and Met). The differential accumulation of those metabolites could be associated with the differential heat tolerance between C₃ Kentucky bluegrass and C₄ bermudagrass.     

Effects of CO2 enrichment,nutrient addition,and fungal endophyte-infection on the growth of two grasses

Summary Increasing atmospheric carbon dioxide (CO₂) concentration is expected to increase plant productivity and alter plant/plant interactions, but little is known about its effects on symbiotic interactions with microorganisms. Interactions between perennial ryegrass, Lolium perenne (a C3 plant), and purpletop grass, Tridens flavus (a C4 plant), and their clavicipitaceous fungal endophytes (Acremonium lolii and Balansia epichloe, respectively) were investigated by growing the grasses under 350 and 650 l l^– 1 CO₂ at two nutrient levels. Infected and uninfected perennial ryegrass responded with increased growth to both CO₂ enrichment and nutrient addition. Biomass and leaf area of infected and uninfected plants responded similarly to CO₂ enrichment. When growth analysis parameters were calculated, there were significant increases in relative growth rate and net assimilation rate of infected plants compared to uninfected plants, although the differences remained constant across CO₂ and nutrient treatments. Growth of purpletop grass did not increase with CO₂ enrichment or nutrient addition and there were no significant differences between infected and uninfected plants. CO₂ enrichment did not alter the interactions between these two host grasses and their endophytic-fungal symbionts.     

氧化石墨烯对多年生黑麦草逆境生理及光合特征的影响

为探讨不同浓度氧化石墨烯（GO）对多年生黑麦草生长、生理及光合特征的影响,该文采用盆栽试验,在土壤中添加0、10、20、30、40、50 mg·g^-1 GO进行多年生黑麦草培养,并测定植物生长指标、光合色素含量、保护酶活性、丙二醛（MDA）含量、叶片质膜透性、可溶性蛋白含量和光合参数。结果表明：（1）10、20 mg·g^-1 GO处理对多年生黑麦草生长无显著影响;30～50 mg·g^-1 GO处理对多年生黑麦草生长具有抑制作用,在50 mg·g^-1 GO浓度下多年生黑麦草株高和生物量均最小,较对照分别降低了16.8%和27.1%。（2）当GO浓度达到30 mg·g^-1时,总叶绿素和类胡萝卜素的含量显著降低,在50 mg·g^-1 GO处理时达到最低。（3）高浓度的GO处理(40、50 mg·g^-1)虽降低了多年生黑麦草的叶片净光合速率（P_n）、气孔导度（G_s）和蒸腾速率（T_r     

A novel DNA-based diagnostic test for the detection of annual and intermediate ryegrass contamination in perennial ryegrass

Perennial ryegrass (Lolium perenne L.) is a preferred choice for the turf grass industry due to its ability to provide a durable turf cover. Genetic or physical contamination of annual (L. multiflorum Lam.) or intermediate (L. hybridum) ryegrass species in perennial ryegrass is one of the major problems affecting the grass seed industry. At present, seedling root fluorescence (SRF), a biochemical marker, is used for the detection of annual ryegrass contamination. Due to the unreliability of the SRF test, the seed industry is seeking an alternative, more reliable and accurate detection method. Currently, there are no DNA tests available in ryegrass for detecting contamination with annual and intermediate ryegrass types. We developed a novel quantitative polymerase chain reaction (Q-PCR)-based DNA test for the detection of annual and/or intermediate ryegrass types in perennial ryegrass. This DNA test was designed using an insertion/deletion (InDel) site in the LpVRN2_2 (Vernalization 2) gene, which is one of the several genes controlling vernalization in ryegrass. The new DNA test is more reliable, accurate and cost-effective in detecting contamination, with a high sensitivity of 0.04% in a sample size of 5,000 seeds. Use of larger sample sizes (12.5-fold higher compared to SRF test) provided additional accuracy in detecting the level of contamination. The method has produced consistent results in 68 perennial, 26 annual and 14 intermediate ryegrass lines.     

Endophyte infection in perennial ryegrass reduces the susceptibility of black cutworm to an entomopathogenic nematode

Abstract The perennial ryegrass, Lolium perenne, forms a symbiotic relationship with Neotyphodium lolii, a fungus that produces alkaloids. This relationship provides a competitive advantage to the host plant in grassland communities by increasing drought tolerance, and disease and herbivore resistance. Black cutworm, Agrotis ipsilon, is among the few insect species that are able to feed and develop on endophytic perennial ryegrass. Some insects can use plant secondary compounds to defend themselves against predators, therefore we hypothesized that the cutworms fed on endophytic grasses would exhibit greater defense against a lethal endoparasitic nematode, Steinernema carpocapsae. Laboratory experiments involving 4–5th instars support the hypothesis that A. ipsilon feeding on grass clippings from field plots with high (> 90%) incidence of endophyte infected perennial ryegrass are less susceptible to entomopathogenic nematodes than larvae fed grass clippings from plants with little or no incidence of endophyte. Laboratory studies resulted in similar overall mortality after 48 h. Field studies, however, show decreased susceptibility to S. carpocapsae when larvae were confined to areas of endophytic grass (> 75% infected). Early instars (2–3rd) fed on endophyte free grass suffered greater overall mortality at all nematode concentrations than 4–5th instars fed similarly. Early (2–3rd) instars were equally susceptible to nematode attack regardless of food source. Our results indicate that the fungal endosymbionts of grasses can influence the biology of natural enemies of an herbivorous insect.     

Enhanced drought tolerance in transgenic Leymus chinensis plants with constitutively expressed wheat TaLEA3

Leymus chinensis is an important grassland perennial grass. However, its drought tolerance requires to be improved. LEA (late embryogenesis abundant) genes are believed to confer resistance to drought and water deficiency. Using Agrobacterium-mediated transformation, a wheat LEA gene, TaLEA ₃ , was integrated into L. chinensis. The transgenic lines showed enhanced growth ability under drought stress during which transgenic lines had increased the relative water content, leaf water potential, relative average growth rate, but decreased the malondialdehyde content compared with the non-transgenic plant. Thus, transgenic breeding is an efficient approach to enhance drought tolerance in L. chinensis.     

Olfactory response of Costelytra zealandica (Coleoptera: Melolonthinae) to the roots of several pasture plants

The influence of natural plant odours on the locomotory behaviour of 3rd‐instar larvae of Costelytra zealandica (White) was studied by observing their movement in glass‐sided test chambers. Through an analysis of the paths followed by individual larvae in single‐option choice‐chamber tests it was possible to evaluate the responses of the larvae to different plant materials. The odour of fresh young perennial ryegrass (Loliumperenne) root was more attractive to the insects than was that of older plants. Larvae were also more strongly attracted to the root of lucerne (Medicago sativa), Lotus pedunculatus, red clover (Trifolium pratense), and white clover (T. repens) than to that of perennial ryegrass. The possible role of volatile chemical factors in plant resistance to grass grub attack is discussed.     

Breeding for Bio-ethanol Production in Lolium perenne L.: Association of Allelic Variation with High Water-Soluble Carbohydrate Content

Increasing the extractable sugar yield from perennial crops is one strategy to generate renewable fuels such as bio-ethanol. Lolium perenne L. (perennial ryegrass) can contain significant (>30% dry matter) water-soluble sugars in the form of polymeric fructan which is readily extracted, broken down and fermented to bio-ethanol. A population of L. perenne generated from four parents which differed in water-soluble carbohydrate (WSC) content was subjected to multiple rounds of selection and recombination on the basis of early spring WSC content to produce a high WSC, and a low WSC population. A control population was generated by selecting the same number of plants at random. The alleles present at six candidate gene loci were analysed before and after selection and correlated to WSC content. Significant differences in the allele frequency of L. perenne soluble-acid invertase1:4 were observed between the three populations with one haplotype significantly associated with the high WSC C2^S+ population (after three rounds of selection and two rounds of recombination). Moreover, WSC content was also associated with biomass accumulation. Thus, in addition to a 2.84-fold increase in WSC yield, the C2^S+ population also had 1.48-fold more biomass per plant, resulting in 3.9-fold higher WSC yield per plant than the control population.     

Fungal endosymbionts affect aphid population size by reduction of adult life span and fecundity

The symbiosis between grasses and endophytic fungi is a common phenomenon and can affect herbivore performance through acquired, chemical plant defence by fungal alkaloids. In laboratory experiments, two species of common grass aphids, Rhopalosiphum padi and Metopolophium dirhodum were tested, in a population experiment (on four plant cultivars) and individually (on one plant cultivar) for the effects of the endophyte, Neotyphodium lolii, that forms symbiotic associations with perennial ryegrass Lolium perenne. In the population experiment that lasted for four aphid generations both aphid species showed decreased population sizes when feeding on each of the four endophyte-infected cultivars. Individuals of R. padi tested individually showed reduced adult life span and fecundity when feeding on infected plants. Individuals of M. dirhodum showed no response in any of the traits measured. This suggests that R. padi individuals are more sensitive to endophyte infection than M. dirhodum individuals. However, all infected grass cultivars reduced population sizes of both aphid species over four generations. Therefore, fungal endophytes can reduce populations of aphid herbivores independent of plant cultivars.     

Leaf functional trait variation associated with salt tolerance in perennial ryegrass

Salinity is one of major environmental stresses that dramatically threaten plant growth, and variations in genetic structure and functional traits have important effects on the salt tolerance of perennial ryegrass (Lolium perenne L.). The objectives of this study were to: (i) assess the inter‐clonal variation of functional traits of accessions among geographic groups or between wild and commercial groups in response to salt stress; (ii) develop a mathematical model to effectively assess salt tolerance of perennial ryegrass accessions originating from different geographic populations; and (iii) determine the relation between spatial genetic structure and salt tolerance in perennial ryegrass. Wide variations were found among the accessions for seven functional traits. One regression model (F = 0.49 × F₁ + 0.303 × F₂ + 0.207 × F₃) was established to ascertain salt tolerance of each accession. The highest variation of the traits and salt tolerance were obtained for accessions from the European group. Wild accessions exhibited more variation in functional traits and salt tolerance than commercial cultivars. Both molecular marker techniques and functional traits were used to conduct phylogenetic analysis, and the majority of accessions from the same or adjacent regions were clustered into the same group or subgroup. The perennial ryegrass accessions with similar salt tolerance had a close phylogenetic background. The patterns in functional trait variations associated with salt tolerance might allow acceleration of the process for improving salt stress resistance in perennial ryegrass.     

Effect of annual and perennial cropping regimes in microplots on the population density and vertical distribution of Xiphinema diversicaudatum and on soil porosity

Long-term trends in populations of Xiphinema diversicaudatum were measured in two microplot experiments in which annual and perennial crops of seven plant families were grown in monoculture. Numbers of X. diversicaudatum increased under perennial ryegrass, raspberry and strawberry but decreased under hop, spring barley, potato, sugar beet, cabbage, winter wheat and winter beans; these effects probably reflected differences in the inherent host status of the crops. There were fewer X. diversicaudatum at 40–60 cm below annual crops than below perennial crops, and there were differences between perennial crops in nematode vertical distribution. Soil pore space did not limit nematode population density; total pore space was uniformly large under all crops and there was no detectable instability to water slaking. Under ryegrass a greater proportion of soil volume was occupied by pores too small to accommodate X. diversicaudatum, but since ryegrass supported the second largest nematode population, it seems unlikely that this was seriously limiting.