Optimal germination conditions for monitoring seed viability in wild populations of fescues

Aim of study: Germination assays are vital in the management of material preserved in germplasm banks. The rules published by the International Seed Testing Association (ISTA) are generally those followed in such assays. In wild species, seed dormancy and inter-population variability increase the difficulty in estimating seed viability. The aim of the present work was to determine the germination requirements of the seeds from different wild populations of pasture grasses species. Area of study: Northwestern Spain Material and methods: Seeds from eight wild populations of different species of Festuca, all from northwestern Spain, were studied. Germination assays were performed under constant and alternating temperature conditions. Treatments for removing seed dormancy (cold stratification and gibberellic acid application) were also applied. A full parametric time-to event model was used for data analysis. Main results: In general, the optimum environmental temperature for germination was around 15°C for the populations of Festuca group ovina, F. gr. rubra and F. gigantea; temperatures of 20-30ºC had a negative effect. All the examined populations, except that of tall fescue (Lolium arundinaceum), showed non-deep physiological dormancy at suboptimal germination temperatures, but this was breakable by the application of gibberellic acid and by cold stratification. Research highlights: There are clear inter- and intra-specific differences in germination requirements that might be associated with place of origin. The ISTA germination assay recommendations for wild members of fescues may not be the most appropriate.

Biology and non-chemical management of Spermacoce verticillata and Spermacoce densiflora

The weed species Spermacoce densiflora DC. and Spermacoce verticillata L. have shown an increase in their occurrence in cultivated areas in the northeast region of Brazil, and field observations have reported their ineffective control with chemicals. This study aimed to evaluate the germination of S. densiflora and S. verticillata under constant (15, 20, 25, 30 and 35°C) and alternating temperatures (20–30°C) in dark and in constant light; the emergence of seedlings from seven sowing depths (0, 0.5, 1, 2, 4, 6 and 10 cm); the emergence of seedlings under five types of cover crop straw (Crotalaria juncea L., Pennisetum glaucum (L.) R. Br., Sorghum bicolor (L.) Moench, Dolichos lablab L., and Cajanus cajan L.) and four amounts (nil and the average, half and twice the amount of straw produced in the field); and germination at different aqueous cover crop extract concentrations (0, 20, 40, 60 and 100%) to measure allelopathic potential of cover crop straw. The results showed that S. densiflora has positive photoblastic behavior. The alternating temperature provided the highest percentage of germination and germination speed index (GSI) for both species. S. densiflora and S. verticillata seedling emergence decreased with an increase in depth, with no germination at a depth of 10 cm. The presence of straw impaired the emergence of seedlings of S. densiflora and S. verticillata by delaying and even preventing germination from occurring. The gradual increase in the aqueous extract concentrations was accompanied by lower percentages of germination and GSI for S. densiflora and S. verticillata.

Fire Resistance and Seismic Performance Study of a High-Strength Construction Steel Using Creep and Internal Friction Analysis

Fire resistance and seismic performance are the two of the most important considerations for the design of construction steel. The fire resistance of the high-strength construction steel, Q460FRE, which contains low Mo, was investigated by means of creep test under different experiment conditions. Then, the seismic performance of the Q460FRE steel, after being subjected to various fire temperatures, was characterized by internal friction analysis. The Q460FRE steel exhibited excellent fire resistance, and the yield strength at 600 °C was 67.4% of the yield strength at room temperature. The constitutive equation of creep stress and fracture time at 600 °C was established. The bearing tensile stress of the Q460FRE steel should be lower than 337 MPa to ensure at least 1 hour to evacuate from the fire. The creep stress and alternating temperature significantly affected the serration behavior of the creep strain. The internal friction analysis indicated that the seismic performance of the Q460FRE steel decreased with the increase in fire temperature, being consistent with the analysis results of the seismic performance characterized by the yield ratio.

Differential germination characteristics of glyphosate-resistant and glyphosate-susceptible Chloris virgata populations under different temperature and moisture stress regimes

Thorough knowledge of the germination behavior of weed species could aid in the development of effective weed control practices, especially when glyphosate resistance is involved. A study was conducted using two glyphosate-resistant (GR) (SGW2 and CP2) and two glyphosate-susceptible (GS) (Ch and SGM2) populations of Chloris virgata, an emerging and troublesome weed species of Australian farming systems, to evaluate their germination response to different alternating temperature (15/5, 25/15 and 35/25°C with 12 h/12 h light/dark photoperiod) and moisture stress regimes (0, -0.1, -0.2, -0.4, -0.8 and -1.6 MPa). These temperature regimes represent temperatures occurring throughout the year in the eastern grain region of Australia. Seeds germinated in all the temperature regimes with no clear indication of optimum thermal conditions for the GR and GS populations. All populations exhibited considerable germination at the lowest alternating temperature regime 15/5°C (61%, 87%, 49%, and 47% for Ch, SGM2, SGW2, and CP2, respectively), demonstrating the ability of C. virgata to germinate in winter months despite being a summer annual. Seed germination of all populations was inhibited at -0.8 and -1.6 MPa osmotic potential at two alternating temperature regimes (15/5 and 35/25°C); however, some seeds germinated at 25/15°C at -0.8 MPa osmotic potential, indicating the ability of C. virgata to germinate in arid regions and drought conditions. Three biological parameters (T10: incubation period required to reach 10% germination; T50: incubation period required to reach 50% germination; and T90: incubation period required to reach 90% germination) suggested late water imbibition with increasing moisture stress levels. The GR population SGW2 exhibited a distinctive pattern in T10, T50, and T90, possessing delayed germination behaviour and thus demonstrating an escape mechanism against pre-plating weed management practices. Knowledge gained from this study will help in developing site-specific and multi-tactic weed control protocols.

Cenários de mudanças climáticas influenciando a germinação e vigor de sementes de Mimosa tenuiflora e Cenostigma pyramidalis

<span class="fontstyle0">Climatic changes occurring on the planet can cause problems in the physiological behavior of plant seeds from the Caatinga biome. The objective of this research was to evaluate a reference scenario to climate changes in the germination and vigor of Mimosa tenuiflora and Cenostigma pyramidalis seeds. For this, different treatments of environmental stress (combinations of temperature, relative humidity, luminous intensities, and water stresses) were tested on seeds of M. tenuiflora and C. pyramidalis. Using Gerbox boxes with vermiculite substrate, the assays were assembled in CRD, and evaluated for variations related to germination and seed and seedlings vigor. The results obtained were obtained by ANOVA and by the Scott-Knott means test. The germination and vigor of M. tenuiflora seeds and seedlings were reduced after a temperature of 30°C. C. pyramidalis seeds germinated only under conditions of alternating temperature, absence of water stress and cannot tolerate temperatures above 30°C. Climatic changes can affect the germination and vigor of the studied species. Research with this theme must be carried out to improve the management of these species in relation to the effects of climate changes.</span> <br /><br />

Analysis and control of state jump in space deployable structures under alternating temperature loads

State jump has been experimentally observed in space deployable structures working in alternating temperature environments. State jump is a phenomenon in which the geometric shape of the structure changes after the temperature loading and unloading process, which makes the working accuracy of the space deployable structure intrinsically unpredictable. This paper aims to investigate the causes of this state jump phenomenon and seek measures to reduce its effect. Firstly, the static multiple-stable-state phenomenon resulting in state jump is analyzed for clearance joints in deployable structures. Then, an equivalent model consisting of a variable stiffness spring and a contact element for state jump analysis is proposed, which is verified by a finite element simulation. Influence factors and control methods of state jump are further explored. Finally, numerical results of a space deployable structure of an umbrella-shaped antenna show the effectiveness of the developed analytical method.

Germination biology of four climatically varied populations of the invasive species African lovegrass (Eragrostis curvula)

African lovegrass [Eragrostis curvula (Schrad.) Nees] is a highly invasive C4 perennial grass that threatens global biodiversity. Appropriate management of this species has been hampered by a lack of knowledge concerning its seed ecology, resulting in significant economic and environmental impacts within various environments. Consequently, this study explored the effects of a selection of environmental factors (photoperiod, alternating temperature, pH, and salinity) by analyzing several measures of germination on four geographically distinct populations of E. curvula to assist in its extirpation from infested sites. Seeds were collected in Australia from Maffra and Shepparton, VIC; Tenterfield, NSW; and Midvale, WA. Key results showed that seeds from Maffra (54% vs. 79%), Tenterfield (38% vs. 61%), and Shepparton (34% vs. 71%) had significantly reduced germination in complete darkness compared with an alternating 12-h light and 12-h dark photoperiod, whereas Midvale had consistent germination (91% vs. 99%). Temperatures between 17/7 C reduced germination for Maffra (42% vs. 73%), Tenterfield (34% vs. 55%), and Shepparton (33% vs. 59%) compared with the mean of all other temperature combinations, whereas Midvale had consistent germination. Furthermore, germination for all populations was consistent between pH 4 and 9. For salinity, germination was significantly reduced at ≥100 mM for Maffra (29% vs. 67%), ≥150 mM for Tenterfield (29% vs. 94%) and Shepparton (39.5% vs. 81.5%), and 250 mM for Midvale (39% vs. 82%) compared with the mean of all other concentrations. Although each trial was conducted independently, the data can be used to generate species-targeted management. Such strategies include maintaining high levels of quarantine and hygiene programs to avoid future spread; where practical, applying light-limiting strategies (mulching, tilling, or scraping) for the Maffra, Tenterfield, and Shepparton populations; and maintaining management efforts year-round, as the species can germinate under a wide range of conditions.