Reduced Seedling Emergence Research Articles

The Impact of Parthenium Weed-Amended Substrates on the Germination and Early Growth of a Range of Pasture and Crop Species

Parthenium weed (Parthenium hysterophorus L.) is an internationally important invasive weed native to the tropical and sub-tropical Americas, and invasive in more than 30 countries. This weed has serious adverse influences on rangeland and agricultural crop production, on human and animal health, and on the biodiversity of natural communities. Parthenium weed leaf litter can reduce seedling emergence and affect the early growth of a wide range of pasture and crop species. Soil collected from a heavily infested parthenium weed area was shown to reduce seedling emergence of a wide range of test plants (lettuce (Lactuca sativa L.), maize (Zea mays L.), curly windmill grass (Enteropogon acicularis L.), and liverseed grass (Urochloa panicoides P.Beauv.)) by between 20 to 40%; however, the soil had no effect on the subsequent growth of the surviving test plants. Soil amended with dried parthenium weed leaf litter reduced the emergence of test species by ca. 20 to 40%, but it had no effect on the growth of the surviving test plants. One week after emergence, the growth of all test species was stimulated by 9 to 86% in the leaf litter-amended soil with the increased growth matching the increased amounts leaf litter amended. In parthenium weed-infested landscapes, the substrate (soil) is affected by the plant during the growing season by the release of allelopathic chemicals. However, the plant’s litter can affect the community outside of the growing season, first through a residual allelopathic activity, but also by a fertilizing effect as litter breakdown occurs. This study demonstrates the significant ability of parthenium weed to affect plant communities throughout the year and, when considered over several years, this may lead to the creation of a complete monoculture of the weed.

Seed Treatment With Jasmonic Acid and Methyl Jasmonate Induces Resistance to Insects but Reduces Plant Growth and Yield in Rice, Oryza sativa.

When applied exogenously to plants, jasmonates [i.e., jasmonic acid (JA) and methyl jasmonate (MeJA)] increase plant resistance against herbivores, and their use in pest management has been suggested. For integration into pest management programs, the benefits of the resistance induced by jasmonates must outweigh the costs of jasmonates on plant growth and yield. A previous field study in rice found that seed treatment with MeJA reduced densities of the rice water weevil, Lissorhoptrus oryzophilus, but also reduced plant growth. Yields from MeJA plots were similar to yields from control plots. Because this study was conducted under field conditions with natural levels of pest populations, it was unclear whether effects on growth and yield were due to direct effects of MeJA treatment on the plant or due to lower reductions in rice water weevil densities. Therefore, the present study was designed to characterize the effects of JA and MeJA seed treatment on rice plant growth and yield in a pest-free environment under greenhouse conditions. Seed treatment with 2.5 mM JA and 2.5 mM MeJA enhanced resistance in rice plants to rice water weevils when plants were exposed to weevils 30 days after planting. Seed treatment with MeJA reduced seedling emergence and plant height at 4 and 14 days after planting, respectively, compared to JA and control treatments. However, numbers of tillers per plant at 45 days after planting and days to heading were unaffected by jasmonate seed treatment. Of four yield components (panicles per plant, filled grains per panicle, percent unfilled grains, and filled grain mass) that were measured, only filled grain mass was reduced by seed treatment. Plants grown from MeJA-treated seeds showed 31% lower grain masses compared to plants grown from control-treated seeds. Thus, the effects of seed treatment with MeJA on plant growth were stronger immediately post-treatment and subsided over time, such that plant growth mostly recovered 6 weeks after treatment. At maturity, MeJA may reduce one but not all components of yield. Despite similar effects on rice water weevil resistance, the negative effects of JA seed treatment on plant growth and yield were smaller compared to MeJA seed treatment.

Seed dormancy of Lolium perenne L. related to the maternal environment during seed filling

AbstractLolium perenne L. (perennial ryegrass) shows variable levels of seed physiological dormancy (PD), which depends on the genotype and environmental condition during seed development. To analyse the effect of field temperature and precipitation during seed filling on the PD, two cultivars were sown on five dates in 2014 and 2015. After harvest, the level of seed PD was 4–28%. High-temperature stress (>29°C) in the field during seed development, measured as heat stress units (HSUs), reduced seed PD (increased germination) at harvest. After 9 months of dry afterripening under laboratory conditions, mean dormant seed values were reduced from 15 ± 8 to 8 ± 7%. An increment in the seed PD level reduced seedling emergence in the field. Seed with 20% PD produced only 50% of field emergence, under optimal environmental conditions. Different vigour tests were conducted and each was compared with field emergence. The speed of germination, through the first count at 5 d of the standard germination test, and the shoot length at 10 d were better associated with the seedling establishment in the field. The HSU could be useful to establish a possible PD range in the seed of perennial ryegrass after the growing season. The development of models considering the HSU and other climatic parameters could motivate future studies.

The effect of environmental and management factors on seed germination and seedling emergence of Asian spiderflower (Cleome viscosa L.)

AbstractAsian spiderflower (Cleome viscosa L.) is a fast‐growing herb found in humid and warm habitats of the Americas, Africa and Asia. It is one of the most important weeds of crop fields in Asia and Africa. The objective of this study was to determine the after‐ripening of Asian spiderflower seeds and evaluate its germination and emergence responses to various environmental (temperature, pH, salinity and water potential) and management (burial depth, flooding time and high temperature) factors. Mature seeds were collected from Kalaleh County, Iran, during October of 2015 and 2018. Seed germination increased over time and reached 77% after 209 days after‐ripening. Based on the segmented model, base and optimum temperatures for germination were 15.70–17.32°C and 31.89–34.11°C respectively. Asian spiderflower seed germination was sensitive to high levels of soil salinity and adapted to moderate‐drought conditions. Seeds germinated better at neutral and alkaline pH levels. Seedling emergence from seeds either left on the soil surface or buried at depths more than 4 cm was low, and the maximum emergence occurred in seeds buried at a depth of 1 cm. Flooding significantly reduced seedling emergence. The exposure of seeds to 82.18–87.59°C reduced seed germination by 50% and no germination occurred at 100°C. The results obtained from this study showed that several options are available for the integrated management of this weed.

Growth and fecundity of colonizing hybrid Raphanus populations are environmentally dependent.

Hybrid gene pools harbor more genetic variation than progenitor populations. Thus, we expect hybrid populations to exhibit more dynamic evolutionary responses to environmental variation. We ask how environmental variation experienced by adapted and transplanted populations influence the success of late-generation hybrid populations during invasion. For four generations, 20 wild (Raphanus raphanistrum) and 20 hybrid radish (R. sativus × R. raphanistrum) plant populations evolved under experimentally manipulated moisture conditions (dry, wet, control-sheltered, or control-unsheltered plots; i.e., evolutionary environment) in old fields near Toronto, Canada. We planted advanced-generation wild and hybrid radishes in sheltered plots and exposed them to either an evolutionary or a novel watering environment. To determine how soil moisture would influence invasion success, we compared the phenotype and fecundity of plants grown in these various environments. Hybridization produced larger plants. In wet environments, hybrid seedlings emerged more frequently and expressed higher photosynthetic activity. Low-moisture, novel conditions delayed and reduced seedling emergence frequency. Hybrid plants and those that evolved under relatively wet environments exhibited higher aboveground biomass. Hybrid plants from control-sheltered plots colonizing novel moisture environments were more fecund than comparable wild plants. Dry environments are less likely than other evolutionary environments to contribute colonists. However, relatively wet locations support the evolution of relatively fecund plants, especially crop-wild hybrid populations. Thus, our results provide a strong mechanistic explanation for variation in the relative success of crop-wild hybrids among study locations and a new standard for studies that assess the risk of crop-wild hybridization events.

Ecological fitness cost associated with the AHAS Trp574Leu mutation in feral Raphanus sativus

AbstractGene mutations endowing herbicide resistance may have negative pleiotropic effects on plant fitness. Quantifying these effects is critical for predicting the evolution of herbicide resistance and developing management strategies for herbicide‐resistant weeds. This study reports the effects of the acetohydroxyacid synthase (AHAS) Trp574Leu mutation throughout the life cycle of feral radish (Raphanus sativus L.). Resistant and susceptible phenotypes responded differently to light and water treatments in relation to germination and emergence. Under light exposure, the resistant phenotype showed higher germination and emergence, but no differences were found in seed dormancy, germination in darkness and emergence from buried seeds or pods. The resistant phenotype showed delayed and reduced seedling emergence relative to the susceptible phenotype under rainfed conditions, but these differences between the phenotypes were not detected in irrigated soil. The phenotypes showed similar relative growth rates and vegetative biomass. However, under wheat competition, resistant plants had 36%–46% less total above‐ground biomass, 26%–47% less seeds per plant and 36%–53% less plant yield than susceptible ones, and these differences were more evident at higher plant density. This study provides a better understanding of the ecological fitness cost associated with the AHAS Trp574Leu mutation in feral R. sativus. The fitness costs could reduce the frequency of the resistant allele in areas untreated with AHAS‐inhibiting herbicides. Our results suggest that incorporating non‐AHAS herbicidal approaches into integrated weed‐management programmes and maintaining fence lines and fields margin as refuges of susceptible plants provides an opportunity to minimize or reverse herbicide resistance evolution.

Selective herbicide control: using furrows and carbon seed coatings to establish a native bunchgrass while reducing cheatgrass cover

Invasion by exotic grasses is degrading dryland ecosystems worldwide and efforts to restore native vegetation in invaded areas have been largely unsuccessful. Control of invasive grasses with herbicide also limits restoration efforts using native seed. In this study, we evaluated two approaches that could allow for the restoration of a native species Pseudoroegneria spicata while reducing an invasive annual grass Bromus tectorum with a herbicide mixture in the sagebrush steppe ecosystem (the United States). We used two methods to protect native seeds from herbicide: activated carbon was applied as a seed coating with the intent of absorbing the herbicide around the seed, and furrows were used to side‐sweep soil sprayed with herbicide away from the planted seed. Our results indicate that imazapic + glyphosate herbicide application had a strong negative effect on the invasive annual grass, reducing B. tectorum cover 91% after 1 year, and 39% after 2 years. Herbicide also had strong negative effects on P. spicata without a carbon‐coating or furrow treatment, reducing seedling emergence 38%, 2‐year plant density 65%, and 2‐year total growth 90%. Both activated carbon seed coatings and furrow treatments limited herbicide effects on P. spicata 2‐year growth, but neither treatment alone mitigated herbicide effects on all life stages. Combining carbon coatings and furrow treatments mitigated harmful herbicide effects on several plant stages (seedling emergence, plant densities, and growth). Our results suggest that combining activated carbon coatings and furrow results in similar establishment of a native perennial as a non‐herbicide seeding and lowers B. tectorum abundance.

Conspecific and heterospecific grass litter effects on seedling emergence and growth in ragwort (Jacobaea vulgaris).

Jacobaea vulgaris Gaertn. or common ragwort is a widespread noxious grassland weed that is subject to different regulation measures worldwide. Seedling emergence and growth are the most crucial stages for most plants during their life cycle. Therefore, heterospecific grass or conspecific ragwort litter as well as soil-mediated effects may be of relevance for ragwort control. Our study examines the effects of conspecific and heterospecific litter as well as ragwort conditioned soil on seedling emergence and growth. We conducted pot experiments to estimate the influence of soil conditioning (with, without ragwort), litter type (grass, ragwort, grass-ragwort-mix) and amount (200 g/m², 400 g/m²) on J. vulgaris recruitment. As response parameters, we assessed seedling number, biomass, height and number of seedling leaves. We found that 200 g/m² grass litter led to higher seedling numbers, while litter composed of J. vulgaris reduced seedling emergence. Litter amounts of 400 g/m² had negative effects on the number of seedlings regardless of the litter type. Results for biomass, plant height and leaf number showed opposing patterns to seedling numbers. Seedlings in pots treated with high litter amounts and seedlings in ragwort litter became heavier, grew higher and had more leaves. Significant effects of the soil conditioned by ragwort on seedling emergence and growth were negligible. The study confirms that the amount and composition of litter strongly affect seedling emergence and growth of J. vulgaris. Moreover, while conspecific litter and high litter amounts negatively affected early seedling development in ragwort, those seedlings that survived accumulated more biomass and got taller than seedlings grown in heterospecific or less dense litter. Therefore, ragwort litter has negative effects in ragwort germination, but positive effects in ragwort growth. Thus, leaving ragwort litter on pastures will not reduce ragwort establishment and growth and cannot be used as management tool.

Effects of turf, leaf litter, and soil compaction on emergence and establishment of invasive glossy buckthorn (Frangula alnus)

Perennial invasive plants can be controlled by damaging established vegetative individuals or by preventing establishment of new plants from seed. Less information is available about the latter. We examined how seedling establishment of glossy buckthorn (Frangula alnus), a non-native shrub that invades forests in eastern North America, is affected by four soil surface treatments – grass-dominated turf, oak leaf litter, pine leaf litter, soil compaction – relative to an untreated control (tilled soil). Data on seedling emergence, survival, growth, and reproduction were collected from 1.5 m2 plots (six per treatment) over two years at the Kingman Research Farm, Madbury, NH, USA. Overall, buckthorn success from seed was inhibited by grass turf and facilitated by oak litter, while pine litter effects were complex and soil compaction had no effect. Specifically, relative to control, the turf treatment reduced buckthorn seedling emergence (year 2 only), increased mortality over two years, reduced density of living buckthorn, and prevented fruiting. Oak litter resulted in greater buckthorn seedling height relative to control, while pine litter, although reducing seedling emergence (year 1 only), increased both seedling height and the proportion of plants fruiting in year 2. Across all treatments and control, buckthorn seedling emergence was greatest in June, declining thereafter. Of the four treatments, only grass turf offered some promise of resisting invasion. The mechanism of resistance by turf is not known, but likely involves either more intense competition or higher levels of herbivory associated with turf. The mechanism, as well as the logistics and cost of turf establishment in logged areas, require further exploration.

Improving vegetable production under semi-arid, saline conditions in south-western Madagascar

AbstractAgricultural production on the Mahafaly Plateau in SW-Madagascar has traditionally been based on subsistence rain-fed agriculture, with yields declining as a result of low soil fertility, recurrent droughts, and erratic rainfall. Market-oriented vegetable production in this area may help households improve their nutrition and diversify their income. In field trials between the 2013 and 2016 dry cropping seasons, the feasibility of carrot (Daucus carota L.) and onion (Allium cepa L.) production was assessed by testing effects of manure and charcoal amendments, shading, and seed quality on yields. Due to damage caused by cyclones and strong winds, only data from 2013 and 2016 are reported in this paper. Additionally to the field experiments, effects of salinity on seed germination were also examined under laboratory conditions and in the field. Carrot dry matter (DM) yields were 0.24 to 2.76 t·ha−1 while those of onion were 0.15 to 0.99 t·ha−1 DM. While the combination of manure and charcoal application had only minor effects on crop growth, manure alone increased carrot yield by 26% across years. After one cropping season, manure application reduced soil pH from 9.0 to 8.6 and increased soil Corg from 0.87 to 1.76%, N from 0.08 to 0.14%, and P from 10.6 to 15.1 mg·kg−1. Shading reduced carrot yields from 0.87 to 0.58 t·ha−1 DM in 2013 and from 1.87 to 0.85 t·ha−1 DM in 2016, but increased onion yield in 2013 from 0.24 to 0.62 t·ha−1 DM. Carrot seed procured locally performed better in the field than seed imported from the capital which translated into differences in seedling emergence. Saline irrigation water (electrical conductivity = 7.03 mS·cm−1) reduced seedling emergence rate of carrot from 73 to 20% and for onion from 44 to 28% and unprimed seeds performed better than primed ones. Using shading during the dry season is not advisable for carrot and onion production, but improving seed quality and targeted use of soil amendments (time of manure application, manure quality) may enhance vegetable yields.

Responses of AG1 and AG2 QTL introgression lines and seed pre-treatment on growth and physiological processes during anaerobic germination of rice under flooding

Rice seeds germinating in flooded soils encounter hypoxia or even anoxia leading to poor seed germination and crop establishment. Introgression of AG1 and AG2 QTLs associated with tolerance of flooding during germination, together with seed pre-treatment via hydro-priming or presoaking can enhance germination and seedling growth in anaerobic soils. This study assessed the performance of elite lines incorporating AG1, AG2 and their combination when directly seeded in flooded soils using dry seeds. The QTLs were in the background of two popular varieties PSB Rc82 and Ciherang-Sub1, evaluated along with the donors Kho Hlan On (AG1) and Ma-Zhan Red (AG2) and recipient parents PSB Rc82 and Ciherang-Sub1. In one set of experiments conducted in the greenhouse, seedling emergence, growth, and carbohydrate mobilization from seeds were assessed. Metabolites associated with reactive oxygen species (ROS) scavenging including malondialdehyde (MDA) as a measure of lipid peroxidation, ascorbate, total phenolic concentration (TPC), and activities of ROS scavenging enzymes were quantified in seeds germinating under control (saturated) and flooded (10 cm) soils. In another set of experiments conducted in a natural field with 3–5 cm flooding depths, control and pretreated seeds of Ciherang-Sub1 introgression lines and checks were used. Flooding reduced seedling emergence of all genotypes, though emergence of AG1 + AG2 introgression lines was greater than the other AG lines. Soluble sugars increased, while starch concentration decreased gradually under flooding especially in the tolerant checks and in AG1 + AG2 introgression lines. Less lipid peroxidation and higher α-amylase activity, higher ascorbate (RAsA) and TPC were observed in the tolerant checks and in the AG1 + AG2 introgression lines. Lipid peroxidation correlated negatively with ascorbate, TPC, and with ROS scavengers. Seed hydro-priming or pre-soaking increased emergence by 7–10% over that of dry seeds. Introgression of AG2 and AG1 + AG2 QTLs with seed pretreatment showed 101–153% higher emergence over dry seeds of intolerant genotypes in the field. Lines carrying AG1 + AG2 QTLs showed higher α-amylase activity, leading to rapid starch degradation and increase in soluble sugars, ascorbate, and TPC, together leading to higher germination and seedling growth in flooded soils. Seed hydro-priming or pre-soaking for 24 h also improved traits associated with flooding tolerance. Combining tolerance with seed management could therefore, improve crop establishment in flooded soils and encourage large-scale adoption of direct seeded rice system.

Seed Priming Methods: Application in Field Crops and Future Perspectives

To reach in good plant stand, the life cycle of plants is faced with different critical stages such as uneven seed germination, poor and early seedling growth which ultimately results in low crop yield. It is well known that seed priming enhances germination, reduces seedling emergence time, and improves yield and yield contributing characters of plants. Seed priming is a physiological technique of seed hydration and drying to improve the metabolic process prior to germination to fasten the germination, seedling growth, and crop yield under normal, as well as different biotic and abiotic stress conditions. Many researchers have done a lot of research on seed priming in field crops to enhance the final yield. However, different priming methods and their application in field crops are poorly described. Therefore, this review paper discusses seed priming and its different methods and their application in field crops as well as future perspectives of seed priming.

Mechanical characterization of blends containing recycled paper pulp and other lignocellulosic materials to develop hydromulches for weed control

Spreading of hydromulch as a crop management technique might show important advantages over plastic films for weed control, because it can be applied anywhere in a field, even in orchard and vineyard rows. In the present work, 24 blends were prepared by mixing paper pulp, from recovered paper and cardboard coming from paper mills, with different additives: (a) wheat straw, rice hulls, and substrate used for mushroom cultivation on the one hand as fillers, and (b) rice bran, white glue, sodium silicate, and powered gypsum on the other hand as agglomerating agents. The blends were tested with a texture analyser to evaluate their mechanical properties, testing the puncture resistance (24 blends) and the tensile strength (15 blends). Scanning electron photomicrographs of some blends were obtained in order to explore the relationship between their components and the mechanical properties. The results indicate that a blend prepared with paper pulp, wheat straw sieved at 2.5 mm and gypsum attained the highest stress resistance and tensile strength. An environmentally controlled experiment was performed on this and another hydromulch in which rice husk substituted wheat straw to evaluate their efficiency for reducing weed seedling emergence, using propagules of four common summer weeds. Compared with the control treatment performed, the hydromulches reduced seedling emergence from 64.6% to 95.9%. In general, the percentage of dead seedlings underneath was greater than that which passed through the barrier, making the hydromulches promising tools for preventing seedling emergence and for managing the weed seed bank in field conditions.

Growth, productivity and grain quality of AG1 and AG2 QTLs introgression lines under flooding in direct-seeded rice system

Early flooding after direct seeding induces anaerobic condition during germination or anaerobic germination (AG), which severely reduces crop establishment in both rainfed and irrigated areas. Seeds germinating in flooded soils could encounter hypoxia or even anoxia in severe cases, and this hinders germination and seedling growth. The study evaluated the effects of incorporating two major QTLs, AG1 and AG2, associated with tolerance of flooding during germination into the background of two popular rice varieties and assessed their interactive effects on enhancing crop establishment, and subsequent growth, grain yield and quality under direct seeded rice (DSR) system. Elite near-isogenic lines incorporating QTLs of major effects on AG tolerance (AG1, AG2 and AG1 + AG2) in the backgrounds of the popular varieties PSBRc82 (PSBRc82-AG1, PSBRc82-AG2, PSBRc82-AG1-AG2) and Ciherang-Sub1 (Ciherang-Sub1-AG1, Ciherang-Sub1-AG2, Ciherang-Sub1-AG1-AG2), along with the donors Kho Hlan On (KHN for AG1) and Ma-Zhan Red (MZR, AG2) and the recipients PSBRc82 and Ciherang-Sub1 were grown either under saturated soils or flooded with 3−5 cm water depth immediately after dry seeding. Flooding substantially reduced seedling emergence, survival, plant biomass, grain yield and yield components across genotypes. The reduction in yield was more drastic in the sensitive genotypes. The significant decline in grain yield was mainly attributed to reductions in number of panicle per unit area. The AG1, AG2 QTLs are effective in conferring tolerance of early flooding during germination. AG1 and AG2 introgression lines showed a yield advantage of up to 2.8 t ha−1, under early flooding compared with their recurrent parents. Apparently, introgression of AG1 and AG2 QTLs did not have any negative impact on performance under saturated (control) and flooded conditions with respect to seedling emergence, growth, and yield, though with effect on chalkiness in some backgrounds, which warrant further studies.

Comparative Effects of Salt and Alkali Stress on Antioxidant System in Cotton (Gossypium Hirsutum L.) Leaves

AbstractThis pot experiment was to evaluate how salts (NaCl, Na2SO4) and alkali (Na2CO3+NaHCO3) affect the physiological and biochemical characteristics during the seedling stage of two cotton cultivars (salt-tolerant, L24; salt-sensitive, X45). Salt and alkali stress reduced seedling emergence rate, relative biomass, and chlorophyll content, however, the REC and MDA content increased. Salt and alkali stress increased markedly superoxide dismutase (SOD) activity. Peroxidase (POD) activity increased first and then decreased as the increase of salt and alkali stress. Catalase (CAT) activity initially increased and then decreased as NaCl stress increased. In addition, the SOD activity, REC, and MDA content was markedly higher in salt stress than that in alkali stress. The proline content of L24 was higher than that of X45 under salt and alkali stress. However, glycine betaine and soluble sugar content of L24 was lower than that of X45 under alkali stress. The REC and MDA content of L24 were lower than those of X45, however, the relative biomass, chlorophyll content, SOD, POD, CAT, and Pro were higher than those of X45. In conclusion, salt tolerant cotton cultivars may possess a superior protection effect by increasing antioxidant enzymes activity under salt and alkali stress.

Conspecific leaf litter and root competition inhibits shrub emergence in the Patagonian steppe

A critical stage in the establishment of new individuals is seedling emergence and litter is a main factor affecting this stage. Recent research found that adults of Chuquiraga avellanedae are over-dispersed. Among several mechanisms, this pattern might be due to the negative influences of adults on seedlings through root competition. We performed field and glasshouse experiments to evaluate (i) the effects of C. avellanedae leaf litter and root presence on the emergence of conspecific seedlings, and (ii) the effects of leaf litter type (C. avellanedae litter, inert litter, no litter) and seed burial depth (seed at the surface or buried) on the emergence of C. avellanedae and Nassella tenuis (dominant grass) seedlings. The field experiment demonstrated root competition from adult plants on shrub seedlings, reducing seedling emergence. However, the effect of root competition did not differ between microsites (under-shrubs vs. between-shrubs). We dismiss the effect of allelopathy because inert litter (i.e., plastic leaves) had the same negative effect as C. avellanedae litter, indicating a mechanical effect. The glasshouse experiment revealed a species-specific response of seedling emergence. C. avellanedae litter limits the emergence of conspecific seedlings but was neutral with regard to the emergence of grass seedlings (N. tenuis). No differences in root competition between microsites and reduction of shrub seedlings by litter suggest that the over-dispersed pattern found for C. avellanedae is caused, at least partially, by litter effects on seedling emergence.

Toxicity of zero-valent iron nanoparticles and its fate in Zea mays

Application of nanotechnology has gained remarkable interest in recent years and environmental exposure to nanomaterials is becoming inevitable. Therefore, nanotoxicity problem is gaining more attention. Zero-valent iron nano particles (nZVI) are being used widely for different purposes such as environmental remediation. Excessive amounts of nanomaterials may pose inhibitory effects on growth of plants cultivated in nZVI-affected soils which has been addressed in this research. Moreover, fate of nZVI in plants was investigated in the present study. Plant seeds were exposed to different concentrations of nZVI i.e. 0, 100, 250, 500, 800 and 1000 mg/kg. Z. mays was selected as the model plant in this study and found to be a tolerant plant species in presence of low to moderate levels of nZVI in soil. However, addition of higher doses of nZVI reduced seedling emergence and biomass establishment. Results indicated that the total Fe concentrations in Z. mays treated with nZVI increased compared to the control. Considerably higher accumulation of Fe in roots of Z. mays compared to the shoots in all treatments was found. Results indicated that the total Fe contents in Z. mays treated with nZVI were higher than those in control, with the highest Fe accumulation capacity of 24666.2 µg per pot which was obtained in soil received 500 mg/kg nZVI. Overally, toxic effects of higher doses of nZVI on plants were observed in this study. Intelligent use of nZVI for environmental purposes such as applying low to moderate levels of nZVI in soil remediation activities could remarkably prevent their adverse impacts on plant species, promote plant phytoextraction capability, and reduce nZV emission in the environment.

Adverse effects of non-biodegradable and compostable plastic bags on the establishment of coastal dune vegetation: First experimental evidences

Non-biodegradable and compostable plastic bags on beaches negatively affect the development of coastal dune vegetation by drastically reducing seedling emergence and growth.

Effects of Fusarium avenaceum and Rhizoctonia solani on the growth of soybean in saline soils

Soybean (Glycine max) acreage on the Canadian Prairies has increased rapidly in recent years. Production has expanded into semiarid regions where irrigation and drainage problems often result in the accumulation of salts in the soil. Fusarium avenaceum and Rhizoctonia solani are the two dominant pathogens in the disease complex that cause root rot and seedling blight of legume crops on the Canadian Prairies. The effects of F. avenaceum or R. solani in combination with soil salinity on soybean root rot were evaluated under greenhouse and mini-plot conditions. As expected, inoculation with F. avenaceum or R. solani consistently reduced seedling emergence and increased root rot severity in soybean. At high soil electrical conductivity values and inoculum densities, seedling emergence decreased and root rot severity increased in soybean in both trials with F. avenaceum and R. solani. Twenty short-season soybean cultivars that were well suited for production in Alberta were evaluated for their reactions to inoculation with F. avenaceum or R. solani in a saline soil (21.1 dS m−1). High seedling emergence was observed for cultivars 900Y61, P002T04R, 900Y01, TH27005RR, P001T34R, and 900Y81 in the non-inoculated control, for P002T04R and 900Y61 in the F. avenaceum treatment, and for 900Y61, 900Y81, and 900Y71 in the R. solani treatment. Root rot severity was low for cultivars NSC Portage and 900Y61 in the non-inoculated control and P002T004R in the F. avenaceum treatment. The cultivar 900Y61 also consistently had lower disease severity over the trials in the mini-plot test.

A linuron-free weed management strategy for carrots

AbstractThe development of a linuron-free weed management strategy for carrot production is essential as a result of the herbicide reevaluation programs launched by the Pest Management Regulatory Agency in Canada for herbicides registered before 1995 and the discovery of linuron-resistant pigweed species in Ontario. Field trials were conducted in one of Ontario’s main carrot-growing regions on high organic soils in 2016 and 2017. Pigweed species seedlings were effectively controlled with PRE treatments of prometryn, pendimethalin, S-metolachlor, or glufosinate. POST treatments of pyroxasulfone and metribuzin followed by predetermined biologically effective dose (≥90% control of pigweed seedlings) of acifluorfen, oxyfluorfen, fluthiacet-methyl, and fomesafen achieved excellent crop selectivity and commercially acceptable pigweed species seedling control under field conditions. Carfentrazone-ethyl or fomesafen applied PRE severely reduced seedling emergence and yield in the wet growing season of 2017. This study demonstrated clearly that an alternative linuron-free strategy can be developed for carrots. The strategy of exploring the potential to use the biologically effective dose of selected herbicides to achieve crop selectivity and control of pigweed species seedlings was verified.