Leafy Spurge Seeds Research Articles

Germination of leafy spurge (Euphorbia esula L.) seeds under alternating temperatures: the effects of amplitude, midpoint, and imbibition in gibberellic acid

Germinability of dormant seeds or the capacity to germinate under particular conditions is sometimes enhanced by a diurnal alternating temperature regime relative to a constant temperature. Alternating temperature regimes vary in amplitude (difference between the minimum and maximum) and midpoint (average). The aim of this research was to test the effects of amplitude and midpoint regimes on germination of dormant leafy spurge seed from a Fargo, ND population in water and gibberellic acid (GA3). The optimal regimes for germination in both water and GA3 were 20:30 °C (16 h:8 h) and 20:35 °C (19 h:5 h), which provided amplitudes of 10 °C and 15 °C, respectively, with both conditions having a midpoint temperature of 23.3 °C. However, midpoint temperature of 22 °C to 27 °C were equally effective for germination under the 20:30 °C and 20:35 °C alternating temperature regimes. Additional alternating temperature regimes with amplitudes of 15 °C (15:30 °C and 10:25 °C), 20 °C (10:30 °C), and 25 °C (10:35 °C) generally displayed reduced germination in both water and GA3, which is likely attributable to the low initial alternating temperature (≤15 °C) component of the regime relative to the higher initial temperature of 20 °C for the optimum regimes of 20:30 °C and 20:35 °C. Under the alternating temperature regimes tested, seeds germinated in GA3 generally displayed higher germination (≥80%) compared with seeds in water (30%–50%).

The transcriptomes of dormant leafy spurge seeds under alternating temperature are differentially affected by a germination-enhancing pretreatment

Seed dormancy is an important stage in the life cycle of many non-domesticated plants, often characterized by the temporary failure to germinate under conditions that normally favor the process. Pre-treating dormant imbibed seeds at a constant temperate accelerated germination of leafy spurge seeds under alternating temperatures. However, dormant seeds will also germinate without a pre-treatment, albeit at a much slower rate, which gives rise to longer periods of imbibition before germination. Transcriptome analyses on seeds exposed to prolonged imbibition highlighted pathways associated with phenylpropanoid biosynthesis and interacting networks of genes involved in plant defense. In addition to the many pathways associated with phenylpropanoid biosynthesis enriched with down-regulated genes upon germination, there were also numerous pathways enriched with up-regulated genes associated with energy metabolism, such as glycolysis. Transcriptome data further suggest that metabolism and signaling by the plant hormones ethylene, gibberellin, and abscisic acid are involved in the developmental transition from dormancy to germination. More specifically, sub-network enrichment analysis identified ABI3 as a central hub of a sub-network at germination including several down-regulated genes such as DELLA (i.e., RGL2), which represses gibberellin signaling processes required for germination. The 595-fold increase in the expression of ACC oxidase (ACO4) at germination also suggests an important role for ethylene biosynthesis in germinating leafy surge seeds. Furthermore, the 10–578-fold difference in expression of many genes such as HY5 and Histone H3 between two populations at germination, which were treated with and without a constant temperature germination-enhancing pretreatment, revealed disparate impacts on various biosynthetic, growth, signaling, and response processes. Overall, our results indicate a constant temperature pretreatment (20°C for 21d) is not required for germination of leafy spurge seeds at an alternating temperature. However, the presence or absence of the pretreatment does affect the rate of germination and the germination transcriptional programs.

Changes in the Transcriptome of Dry Leafy Spurge (Euphorbia esula) Seeds Imbibed at a Constant and Alternating Temperature

Leafy spurge seeds are responsive to alternating temperature rather than constant temperature for germination. Transcriptome changes of dry leafy spurge seeds and seeds imbibed for 1 and 3 d at 20 C constant (C) and 20 : 30 C alternating (A) temperature were determined by microarray analysis to examine temperature responsiveness. Principal component analysis revealed differences in the transcriptome of imbibed seeds based on the temperature regime. Computational methods in bioinformatics parsed the data into overrepresented AraCyc pathways and gene regulation subnetworks providing biological context to temperature responses. After 1 d of imbibition, the degradation of starch and sucrose leading to anaerobic respiration were common pathways at both temperature regimes. Several overrepresented pathways unique to 1 d A were associated with generation of energy, reducing power, and carbon substrates; several of these pathways remained overrepresented and up-regulated at 3 d A. At 1 d C, pathways for the phytohormones jasmonic acid and brassinosteroids were uniquely overrepresented. There was little similarity in overrepresented pathways at 1 d C between leafy spurge and arabidopsis seeds, indicating species-specific effects upon imbibition of dry seeds. Overrepresented gene subnetworks at 1 d and 3 d at both temperature regimes related to signaling processes and stress responses. A major overrepresented subnetwork unique to 1 d C related to photomorphogenesis via the E3 ubiquitin ligase COP1. At 1 d A, major overrepresented subnetworks involved circadian rhythm via LHY and TOC1 proteins and expression of stress-related genes such as DREB1A, which is subject to circadian regulation. Collectively, substantial differences were observed in the transcriptome of leafy spurge seeds imbibed under conditions that affect the capacity to germinate.

Alternating temperature breaks dormancy in leafy spurge seeds and impacts signaling networks associated with HY5

Non-after-ripened seeds of the herbaceous perennial weed leafy spurge do not germinate when imbibed at a constant temperature (C), but transfer to an alternating temperature (A) induced germination. Changes in the transcriptome of seeds during 1 and 3days of alternating temperature and germinated seeds were compared with seeds incubated at constant temperature. Statistical analysis revealed that 597, 1,491, and 1,329 genes were differentially expressed (P < 0.05) for the comparisons of 21-day C vs. 21-dayC + 1-day A, 21-day C vs. 21-day C + 3-day A, and 21-day C vs. 21-day C + Germ (germination), respectively. Functional classifications based on gene set and sub-network enrichment analysis were performed to identify pathways and gene sub-networks that underlie transcriptome changes in the seeds as they germinate. Sugars, plant hormones, photomorphogenesis, and reactive oxygen species were overrepresented at 21-day C + 1-day A. At 21-day C + 3-day A, an increase in cellular activities was observed as the number of overrepresented pathways greatly increased. Many of the metabolic pathways were involved in the biosynthesis of amino acids, macromolecules, and energy and carbon skeleton production for subsequent germination. The 21-day C + 3-day A and 21-day C + Germ pathways and sub-networks were similar and included an overrepresentation of the amino acid biosynthetic pathways; however, 21-day C + Germ seeds have an even wider array of cellular activities such as translation-related pathways, which are most likely for seedling growth. RT-qPCR analysis indicated that the up- and down-regulation of HISTONE H3, GASA2, DREBIII-1, CHS, AOS, PIF3, PLD α1, and LEA may be germination-related since their expression was dramatically changed only in the 21-day C + Germ seeds. Finally, both short-term alternating temperature and short-term light exposure up-regulated the expression targets of the central hub HY5 in leafy spurge and Arabidopsis, respectively, indicating that a signaling network involving HY5 is important for germination.

Initial changes in the transcriptome of Euphorbia esula seeds induced to germinate with a combination of constant and diurnal alternating temperatures

We investigated transcriptome changes in Euphorbia esula (leafy spurge) seeds with a focus on the effect of constant and diurnal fluctuating temperature on dormancy and germination. Leafy spurge seeds do not germinate when incubated for 21 days at 20 degrees C constant temperatures, but nearly 30% germinate after 21 days under fluctuating temperatures 20:30 degrees C (16:8 h). Incubation at 20 degrees C for 21 days followed by 20:30 degrees C resulted in approximately 63% germination in about 10 days. A cDNA microarray representing approximately 22,000 unique sequences was used to profile transcriptome changes in the first day after transfer of seeds from constant to alternating temperature conditions. Functional classification based on MIPS and gene ontology revealed active metabolism including up-regulation of energy, protein synthesis, and signal transduction processes. Down-regulated processes included translation elongation, translation, and some biosynthetic processes. Subnetwork analysis identified genes involved in abscisic acid, sugar, and circadian clock signaling as key regulators of physiological activity in seeds soon after the transfer to alternating conditions.

Growth Regulators and Chemicals Stimulate Germination of Leafy Spurge (Euphorbia esula) Seeds

Baseline information on inducing germination of dormant leafy spurge seeds with growth regulators and chemicals is lacking. This study was conducted to survey the effect of various substances on germination of leafy spurge seeds. The nontreated control seeds in this population were nearly fully imbibed in 3 h and displayed approximately 35% germination in 21 d under the normal alternating temperature of 20/30 C (16/8 h). Gibberellic acid (GA3, 10 mM) induced 65% germination at constant temperatures of 20 and 30 C. The alternating temperature increased the effectiveness of 10 mM GA3with 94% germination, a twofold increase over the control. Nontreated seeds did not germinate at the constant temperatures, suggesting that alternating temperature acts via a GA-independent pathway. Kinetin at 0.1 to 1 mM was no more effective than the control, but a saturated solution of kinetin induced 73% germination. Ethephon at 0.01 to 1 mM induced 58 to 66% germination, although there was little response to different concentrations. Ethylene gas at 1 ppm stimulated germination to 77%, a 1.8-fold increase over the control. Germination of seeds incubated continuously in 1 and 10 mM nitrate displayed 35 and 40% germination, respectively. Seeds pulsed for 24 h with 100 mM nitrate displayed 58% germination after 21 d. Potassium phosphate–citrate buffer (pH 3.4) and its individual components induced 60 to 70% germination. Fluridone (10 and 100 µM), 1-naphthaleneacetic acid (NAA, 0.1 to 10 mM), and ethanol (0.2 to 15%) had no effect on germination, but subsequent elongation in the presence of NAA was inhibited because of swelling of the radicle. This research reveals that GA3is the most effective growth regulator for germination of dormant leafy spurge seeds, and its effect is independent of temperature.

Temperature and Moisture Status Affect Afterripening of Leafy Spurge (Euphorbia Esula) Seeds

Abstract Increasing the germination potential of dormant seeds in a population over time generally requires afterripening. Research was conducted to study the relationship between temperature and seed moisture content on afterripening of dormant leafy spurge seeds. Germination of nonafterripened seeds was 59 and 36% after 21 d for the Harwood and Fargo populations, respectively. Germination of 85 to 87% and 58 to 62% was obtained for the Harwood and Fargo populations, respectively when afterripened for 12 to 24 wk under the most effective conditions of 30 C and 2.6% seed moisture; increasing the afterripening temperature to 45 C did not increase germination. Germination decreased slightly at 30 C as the seed moisture content increased to 5.6%, but germination still exceeded that of nonafterripened seeds. Afterripening at 30 C with a seed moisture content of ≥9% greatly decreased germinability due to seed ageing. A temperature of 5 C was effective for afterripening when the moisture content was 3.3%, but g...

Dispersal of Leafy Spurge (Euphorbia esula L.) Seeds in the Feces of Wildlife

Leafy spurge (Euphorbia esula) is an exotic, perennial, invasive weed in many areas of the northern United States and Canada. There are many instances in pastures and wildlands where individual or small clusters of leafy spurge plants are distant and upslope from larger patches, and wildlife have been suspected as seed dispersal agents. Wildlife can disperse seeds by ingestion then excretion of seeds in their feces. Fecal deposits of free-ranging deer (Odocoileus hemionus and O. virginianus; n = 176), sharp-tailed grouse (Tympanuchus phasianellus; n = 201) and wild turkeys (Meleagris gallopavo; n = 206) were collected during a summer in Theodore Roosevelt National Park (TRNP) in western North Dakota, and for deer only in Medicine Lake National Wildlife Refuge (MLNWR) in northeastern Montana. Feces were analyzed for the presence of leafy spurge seeds and any seeds found were tested for germinability and viability. Only one intact leafy spurge seed was found in one grouse fecal deposit and it was not viable. No leafy spurge seed was found in turkey feces. Two seeds that appeared to be immature leafy spurge seeds were found in one deer fecal deposit in TRNP, but neither seed was viable. One leafy spurge seed was found in each of four deer fecal deposits from MLNWR, but only one seed was viable and germinated. Seed-feeding trials with captive deer (n = 4), sharp-tailed grouse (n = 4) and wild turkeys (n = 4) were conducted to determine how leafy spurge seeds interact with the digestive systems of these animals. The only viable seeds defecated by grouse and turkeys were seeds excreted one day after ingestion. Two turkeys did not excrete any leafy spurge seeds and only a few viable seeds were defecated by the other two. One grouse defecated a larger number of viable seeds, but the other three grouse excreted only a few. Deer defecated viable seeds each of 4 d after ingesting them with most viable seed excreted on the first 2 d. These findings, along with those for the free-ranging animals, indicate that wild turkeys probably do not disperse leafy spurge seed while sharp-tailed grouse and deer may do so on a limited basis.

Effect of Sheep Grazing on a Leafy Spurge-Infested Idaho Fescue Community

Leafy spurge (Euphorbia esula L), an aggressive Eurasian forb, is invading native upland ranges dominated by bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Love) and Idaho fescue (Festuca idahoensis Elmer) in the Northern Rocky Mountain Province. Our objective was to determine cumulative effects of 3 summers (1992-1994) of repeated sheep grazing on a leafy spurge infested-Idaho fescue community. Targhee ewes were systematically rotated through paddocks in small pastures. Leafy spurge stem and Idaho fescue and bluebunch wheatgrass plant densities, and frequencies of other species were determined before grazing in 1992, 1993 and 1994, and in 1995, 9 months after grazing ended. Number of viable leafy spurge seeds in seedbanks was determined in 1992 and 1995. Plant heights were measured each year. Density of leafy spurge seedlings was low in grazed and ungrazed areas in 1992 and 1994, whereas density was higher in ungrazed than grazed areas in 1993 and 1995. Grazing did not increase or decrease density of mature leafy spurge stems from 1992 to 1995. Grazing increased density of Idaho fescue but reduced density of bluebunch wheatgrass. Kentucky bluegrass, (Poa pratensis L.), Sandberg bluegrass (Poa sandbergii Vasey), annual bromegrasses (Bromus spp.), and sedge (Carex spp.) frequencies increased in grazed areas. Number of viable leafy spurge seeds in the seedbank was lower in 1995 than in 1992; this reduction was greater in grazed than ungrazed areas. Three years of repeated sheep grazing reduced numbers of leafy spurge seed in the seedbank and seedling densities, but had no effect on density of mature leafy spurge stems. There was minimal effect on the cool season native grasses, possibly because the site was grazed primarily in midsummer when these grasses are dormant. Thus, a long-term commitment to repeated sheep grazing may help to control leafy spurge, although grazed sites should be monitored regularly to ensure that other undesirable species do not increase at the expense of the native plant community.

Recovery of Leafy Spurge Seed from Sheep

Sheep are often used to graze North American rangelands infested with leafy spurge (Euphorbia esula L.), a long-lived perennial forb from Eurasia. Our objective was to determine if sheep grazing infested rangelands disperse leafy spurge seed by transport in their fleece or by depositing seeds in their feces. Twenty-four yearling Targhee ewes grazed a 2.4 ha native bunchgrass range site infested with leafy spurge from late-May through mid-August of 1993 and 1994. Six of the 24 ewes were shorn in October 1993. To recover leafy spurge seeds from those fleeces, we used a standard method to test wool for vegetable matter. On average, 38 seeds were recovered per fleece. During these summers, 6 small groups (n = 4 sheep per group) each grazed 3 separate paddocks. We estimated the density of leafy spurge seed before the groups were moved into 1 of 3 paddocks. After the sheep were moved into a paddock (day 0), we collected fresh feces from each group on or about day 4, 10, and 14. Feces were then washed over sieves to recover leafy spurge seeds. All seeds were tested for germinability and viability. The number of viable seeds excreted daily per ewe was estimated. In 1993, 1,796 +/- 405 (S.E.) leafy spurge seeds m-2 were produced in the field, whereas in 1994, 399 +/- 63 (S.E.) leafy spurge seeds m-2 were produced. The summer of 1994 was much drier than the summer of 1993. We estimated that 41 to 144 leafy spurge seeds were excreted daily per animal in mid-July 1993. Viability of seeds in the feces averaged 5%, whereas viability of seeds collected from seed stalks was 42%. We estimated that the ewes excreted from 2 to 41 leafy spurge seeds daily at the peak in mid-July 1994. Viability of seeds excreted during 1994 averaged 24%, whereas viability of seeds collected from seed stalks was 68%. Sheep can pick up leafy spurge seed in their fleece, and will consume and pass viable seed. However, viability of seed recovered from feces was highly variable and almost always lower than seed collected in the field. Despite reduced seed numbers and viability, sheep have the potential to spread leafy spurge and should be managed accordingly.

Recovery, Germinability, and Viability of Leafy Spurge (Euphorbia esula) Seeds Ingested by Sheep and Goats

Germinability and viability of leafy spurge seeds following ingestion by sheep and goats were evaluated. Four sheep and four goats were separated into eight pens and fed individually a known number of leafy spurge seeds. Following ingestion, goats and sheep passed leafy spurge seeds for 4 and 9 d, respectively. Eighteen percent of the seeds fed were recovered in the fecal material of both species of livestock. Number of seeds recovered, expressed as percent of total seeds fed, decreased with time (P &lt; 0.01). Germinability and viability of the recovered seeds were less than the control (P &lt; 0.01). Sheep were more effective than goats in reducing germinability and viability of leafy spurge seeds (P &lt; 0.01). Results indicate that sheep and goats are effective biological tools for reducing spread of leafy spurge seeds. However, animals grazing mature leafy spurge should be confined for 5 d, until all viable seeds have passed through the digestive system, before they are rotated onto pastures that are devoid of leafy spurge.

Dispersal of Leafy Spurge Seeds (Euphorbia esula) by Mourning Doves (Zenaida macroura)

The potential of mourning doves (Zenaida macrouraL.) as dispersers of leafy spurge (Euphorbia esulaL. # EPHES) seeds was investigated by examing digestive tract contents and feces. Very few intact seeds passed through the digestive systems of wild or captive adult mourning doves. An average of less than one intact leafy spurge seed/g was recovered from fecal material found in dove nests. These results suggest that adult mourning doves are primarily consumers of leafy spurge seeds and rarely act as dispersal agents. It appears that dispersal is only possible when seeds passing through the digestive tracts of nestlings are deposited in the nest and the nest later falls.

Longevity of Leafy Spurge Seeds in the Soil following Various Control Programs

Highlight: Although picloram provided adequate control of leafy spurge (Euphorbia esula L.) for a minimum of 3 years, from 3,500 to 11,000 viable seeds remained in the soil, providing a source for rapid reestablishment of the infestation. Continuous sheep grazing for 8 years prevented annual seed set and reduced the size of the soil seed bank from > 3,500 to 15 seeds/m2, greatly reducing the chance of reestablishment from seed. Combining the data from the various treatments indicated that the average annual loss from the soil seed bank is 13% of the original population. This means that even though an initial application of picloram kills most of the vegetative portion of the plant, a repeat treatment is necessary to greatly reduce the number of seeds in the soil seed bank to prevent reestablishment by seed.