Cultivated sunflower (Helianthus annuus L.) pollen helps attract wild and managed bees needed to produce hybrid seed. Pollen quantity and grain size (≈quality) are affected by the environment, but are also heritable traits of interest for breeding. Florets from public inbred B-lines (maintainer) and R-lines (restorer) were used to evaluate pollen quantity and quality, test for trait correlations and determine if line development has changed pollen traits. Pollen quantity (≈25,000–67,000 grains per floret) and diameter (≈30–37 μm) were similar to previous reports and values of each parameter were correlated across years. Pollen quantity per floret was positively correlated with floret size (area; mm2) but floret sizes and pollen quantity were unrelated to pollen grain size. Groups of lines released relatively early (1968–1986) or late (1988–2006) did not differ in pollen quantity or size, and male (R-line) parents did not produce larger grains. The strong, positive correlation between floret size and pollen quantity reveals a possible trade-off because wild bees generally prefer sunflowers with shallower florets. The apparent lack of change in pollen quantity or pollen grain size over time (and lack of increased pollen size in R-lines relative to B-lines) suggests that the quantity and quality of pollen may not be limiting factors in the success of inbred lines or resulting hybrids. Though sunflower lines with larger florets contain more pollen, additional variation in pollen visible on sunflower heads may relate to the timing or completeness of pollen extrusion from anther tubes.

Rush skeletonweed is an invasive weed in winter wheat (WW)/summer fallow (SF) rotations in the low to intermediate rainfall areas of the inland Pacific Northwest. Standard weed control practices are not effective, resulting in additional SF tillage or herbicide applications. The objective of this field research was to identify herbicide treatments that control rush skeletonweed during the SF phase of the WW/SF rotation. Trials were conducted near LaCrosse, WA, in 2017–2019 and 2018–2020, and near Hay, WA, in 2018–2020. The LaCrosse 2017–2019 trial was in tilled SF; the other two trials were in no-till SF. Fall postharvest applications in October included clopyralid, clopyralid plus 2,4-D, clopyralid plus 2,4-D plus chlorsulfuron plus metsulfuron, aminopyralid, picloram, and glyphosate plus 2,4-D. Spring treatments of clopyralid, aminopyralid, and glyphosate were applied to rush skeletonweed rosettes. Summer treatments of 2,4-D were applied when rush skeletonweed initiated bolting. Plant density was monitored through the SF phase in all plots. Picloram provided complete control of rush skeletonweed through June at all three locations. Fall-applied clopyralid, clopyralid plus 2,4-D, and clopyralid followed by 2,4-D in summer reduced rush skeletonweed through June at the two LaCrosse sites but were ineffective at Hay. In August, just prior to WW seeding, the greatest reductions in rush skeletonweed density were achieved with picloram and fall-applied clopyralid at the two LaCrosse sites. No treatments provided effective control into August at Hay. Wheat yield in the next crop compared to the nontreated control was reduced only at one LaCrosse site by a spring-applied aminopyralid treatment, otherwise no other reductions were found. Long-term control of rush skeletonweed in WW/SF may be achieved by a combination of fall application of picloram, after wheat harvest, followed by an effective burn-down treatment in August prior to WW seeding.

The introduced meadow knapweed (Centaurea × moncktonii C.E. Britton), a hybrid of black (Centaurea nigra L.) and brown (Centaurea jacea L.) knapweeds, is increasingly common in pastures, meadows, and waste areas across many U.S. states, including New York. We evaluated the effects of temperature, light, seed stratification, scarification, and population on percent germination in four experiments over 2 yr. Percent germination ranged from 3% to 100% across treatment combinations. Higher temperatures (30:20, 25:15, and sometimes 20:10 C day:night regimes compared with 15:5 C) promoted germination, especially when combined with the stimulatory effect of light (14:10 h L:D compared with continuous darkness). Under the three lowest temperature treatments, light increased percent germination by 15% to 86%. Cold-wet seed stratification also increased germination rates, especially at lower germination temperatures, but was not a prerequisite for germination. Scarification did not increase percent germination. Differences between C. × moncktonii populations were generally less significant than differences between temperature, light, and stratification treatments. Taken together, these results indicate that C. × moncktonii is capable of germinating under a broad range of environments, which may have facilitated this species’ range expansion in recent decades. However, C. × moncktonii also shows evidence of germination polymorphism: some seeds will germinate under suboptimal conditions, while others may remain dormant until the abiotic environment improves. Subtle differences in dormancy mechanisms and their relative frequencies may affect phenological traits like the timing of seedling emergence and ultimately shape the sizes and ranges of C. × moncktonii populations.

Wild and managed bees are needed to move sunflower (Helianthus annuus L.) pollen, both to create hybrid seed and to encourage high, consistent yields when those hybrids are subsequently grown. Among floral traits that influence bee preference, floret size may be critical, as the depth of the corolla affects the accessibility of nectar. Sampling and observation of inbred maintainer (HA) lines were used to assess variation in floret size, and to measure any effects of floret size on pollinator visitation. Among 100 inbreds sampled, there was significant variation among the lines, with floret lengths of 6.8–9.9 mm. Floret length, measured before anthesis, was closely related to corolla depth during anthesis and was consistent between 2 years (environments). Pollinator observations on 30 inbred lines showed floret size explained a majority (52%) of the variation in wild bee preference, with a reduction in floret length of 2 mm more than doubling pollinator activity. Though honey bee, Apis mellifera L., colonies were located ≈ 60 m from the plots, near-zero honey bee activity in the sunflowers precluded an assessment of how strongly this managed pollinator is affected by floret length. Production of inbreds and hybrids with smaller florets could enhance sunflower pollination, but genetic markers for floret size are needed to facilitate selection, and an understanding of potential trade-offs also is required. Information on variation and heritability of other traits, such as pollen and nectar rewards, could help explain residual variation in wild bee visitation to sunflowers.

Exotic weed propagules (seeds or fruits) often contaminate goods intended for import into Australia. Biosecurity officers must identify such propagules to manage risks, prevent incursions, and decide on potentially costly actions such as cleaning, treating, or destroying cargo. According to observations made by the Australian Department of Agriculture and Water Resources, more than 20% of the propagules found by biosecurity officers currently cannot be identified. By far the most important weed families contributing to seed load of imported goods are the grass family (Poaceae) and the daisy family (Asteraceae), accounting together for approximately 80% of cases. To facilitate fast and secure identification, increase the capabilities of biosecurity staff, and reduce the risk of weed incursions, we have developed an interactive digital identification key to the propagules of an initial priority list of 43 species of Asteraceae.

Yellow starthistle is one of the most important alien invasive weeds in the western United States. It has been targeted for biological control based on the assumption that its abundance is limited by natural enemies in its native region but not in the United States. The geographic center of diversity for yellow starthistle appears to be in Turkey. This region is being explored to discover potential biological control agents; however, there is no quantitative information regarding the population density or dynamics of the plant in this region. Such information could help determine which natural enemies help suppress the plant in its land of origin. We measured densities of yellow starthistle plants and seeds during 2 yr at three locations in central Turkey. Densities of mature plants were about 4% of those measured at sites in California. Densities of capitula and seeds produced were about 60 and 65%, respectively, of those measured in California. The greatest difference between the two regions appears to be the densities of mature plants, which indicates the importance of focusing research on natural enemies that reduce plant survival.

Canada thistle and dandelion are troublesome weeds found throughout the northern United States. Carbohydrate concentrations in roots of these plants change in response to freezing temperatures as plants prepare to overwinter. Herbicides applied in the fall provide more effective control of these weeds than does treatment applied in early spring. Experiments were conducted near Scottsbluff, NE, from 1999 to 2001 to examine changes in glucose, fructose, sucrose, and fructans in roots of Canada thistle and dandelion in response to the fall-applied herbicide. Dicamba applied 10 d after the first fall frost reduced the quantities of low degree-of-polymerization (DP) fructans and provided better control of Canada thistle and dandelion than did dicamba applied 11 d before the first frost. Dicamba and dicamba plus SAN 836H fall-applied were more effective in controlling Canada thistle and dandelion than was 2,4-D fall-applied. As the rate of dicamba and dicamba plus SAN 836H increased, the quantities of low-DP fructans in plant roots declined, and plant control increased. Activity of fructan 1-exohydrolase in roots of Canada thistle was increased by dicamba fall-applied and was closely associated with decline in the quantities of low-DP fructans.

Roots of dandelion were exhumed from the soil monthly from 1997 to 1999 near Scottsbluff, NE, to assess the seasonal changes in total sugars, glucose, fructose, sucrose, and fructans. In the spring, the initiation of plant growth was accompanied by increased fructose and, to a lesser degree, glucose as a percentage of total sugars. During June, July, and August, the percentage of total sugars with a middle to high degree of polymerization (DP) fructans increased. The DP in fructans changed with reduced rainfall and was associated with increased fructose and decreased high-DP fructans as a percentage of total sugars. Decreasing or freezing soil temperatures in the fall were associated with increased fructose and decreased high-DP fructans as a percentage of total sugars. When soil froze in December, the percentage of total sugars as sucrose and low-DP fructans increased and mid- to high-DP fructans decreased. The seasonal fluctuations of glucose, fructose, sucrose, and various fructan polymers may be one mechanism that allows dandelion to adapt to environmental stresses and gain a competitive advantage over other plants in the community. An understanding of these seasonal fluctuations in sugars may also allow better timing of biological, mechanical, and chemical control practices for improved plant management.

Evaluation of Puccinia crupinae, the causal agent of a rust disease on common crupina (Crupina vulgaris), for biological control is described. Susceptibility of accessions of common crupina that represent both varieties of the target from the five populations in the United States indicate that the disease has potential to control common crupina, but differences were noted between accessions on the basis of pustule count, yield (i.e., number and weight of achenes per plant), and shoot dry weight data after multiple inoculations. One accession from Modoc, CA, was not affected in greenhouse tests and would likely not be affected in the field if a permit to release P. crupinae were granted. None of the nontarget species of 26 taxa from the tribes Cardueae and Cichoriae were symptomatic, so the pathogen is likely safe to use in North America.

Understanding seed characteristics and seedling establishment patterns is essential for the development of effective management strategies for invasive annual species. Dittrichia graveolens (stinkwort) has increased its range rapidly within California since 1995, yet its biology is not well understood, which has led to poorly timed management. In this study, seed viability, germination, longevity, and dormancy, as well as seedling emergence characteristics of D. graveolens were evaluated in field, greenhouse, and laboratory experiments in Davis, CA, over a 2-yr period (fall 2010 to summer 2012). In the laboratory, seed germination of D. graveolens occurred at a wide range of constant temperatures (12 to 34 C). Cumulative germination was comparable to total seed viability (80 to 95%) at optimal germination temperatures, indicating that primary (innate) dormancy is likely absent. The base temperature for germination was identified using a thermal time model: 6.5 C and 4 C for 2010 and 2011 seed populations, respectively. In the field, seedlings emerged from fall through spring following precipitation events. A very low percentage of seedlings (2.5%) emerged in the second year after planting. Equivalent seedling emergence was observed over a wide range of light conditions (100, 50, 27, and 9% of available sunlight) in a greenhouse experiment, indicating that seed germination is not limited by high or low light. Results from these seed experiments improve our understanding of the reproductive biology of this rapidly expanding exotic annual and provide valuable information for developing effective timing and longevity of management programs.

Lepidopteran caterpillars are typically classified as herbivorous insects. Other feeding associations have been known for a long time but are often neglected in the ecological literature. In samples from 194 shrubs belonging to 16 species of Piperaceae and Asteraceae, which were taken in a montane forest and succession habitats in southern Ecuador, caterpillar assemblages included an unexpectedly large fraction not feeding on the living biomass of their putative ‘host’. Feeding trials revealed them to instead feed on foliose lichens, dead leaves and epiphylls (lichen, algae, bryophytes). These ‘alternative feeders’ accounted for 22.5% of the whole dataset and up to 80% of the caterpillars on individual plant species. Densities of alternative feeders were very similar across shrub species within each plant family, but differed strongly between Asteraceae in succession and Piperaceae in forest habitats. Herbivore caterpillars showed the opposite pattern with strong differences between individual plant species, but overall similar densities on both plant families.

Although Asteraceae species are important in the cold deserts of Central Asia, little is known about their seed dormancy and germination. We determined dormancy breaking and germination requirements of three annual Asteraceae, Echinops gmelinii, Epilasia acrolasia and Koelpinia linearis. Achenes (seeds) were tested for germination in light and in darkness over a range of alternating temperatures after various periods of burial outdoors and of dry storage. Germination phenology was monitored for seeds sown in irrigated and non-irrigated sand, and temperature requirements for dormancy break were determined under wet and dry conditions. Effects of pericarp and phyllaries on germination of E. acrolasia and E. gmelinii, respectively, were determined. Low percentages of 20-day-old seeds of E. acrolasia and K. linearis were non-dormant and germinated to low percentages over the range of temperatures, whereas all seeds of E. gmelinii were dormant. As seeds of the three species afterripened, they germinated over the range of temperatures. Whether seeds germinated in autumn or spring depended on the amount of sand moisture. Mechanical resistance of the pericarp and phyllaries reduced germination of E. acrolasia and E. gmelinii, respectively. Temperature requirements for germination as seeds come out of dormancy do not correspond to any of the known five types of non-deep physiological dormancy (PD). Thus, a sixth type is recognized in which germination occurs over the same range of temperatures in the early and late stages of dormancy break. Type 6 allows seeds to germinate at high or at low temperatures, whenever sand moisture is non-limiting.

The capitate glandular trichomes of wild sunflowers (Helianthus spp.) are considered to be effective defence components that act against some herbivorous insects, but cultivated sunflowers are reportedly deficient in glandular trichomes. To investigate whether glandular trichomes have a role in the protection of cultivated sunflowers against insects, in the present study, Helianthus annuus L. accessions were grown to quantify glandular trichome density in wild and cultivated germplasm types and assess potential anti-insect effects of terpenoids in the glandular trichomes of cultivated sunflowers. Evaluation revealed that capitate glandular trichomes are often abundant in cultivated sunflowers; relative to wild H. annuus, inbred maintainer (HA) lines have similar numbers of glandular trichomes per floret, while commercial hybrids have only ≈ 20% fewer trichomes when compared with wild sunflowers. In the laboratory assay, it was found that glandular trichome extracts increased the mortality rates of sunflower moth, Homoeosoma electellum (Hulst), larvae exposed from the neonatal stage to 9 d. In the surviving larvae, the extracts significantly reduced larval mass and head capsule width. Though there are limitations to the value of glandular trichomes for host plant resistance, the feeding deterrent or toxic effects of sesquiterpene lactones and diterpenes in sunflower glandular trichomes are not limited to sunflower moth larvae, suggesting a potential for resistance to other sunflower insect pests. Additional research is required to understand the inheritance and value of glandular trichomes in commercial sunflower germplasm and how the composition of terpenoids in the glandular trichomes of wild H. annuus may differ from that in cultivated material.

Gene flow between agricultural crops and related wild plant populations can produce hybrids which differ significantly from their wild counterparts in many life history traits, including seed traits. Seeds from wild annuals often possess significant dormancy, while cultivated varieties have been selected to germinate immediately under favourable conditions. Consequently, the dormancy characteristics of crop–wild hybrids could influence their survival, seed-bank dynamics and, ultimately, the extent to which crop genes persist in wild populations. Dormancy characteristics can be influenced by both maternal effects, as well as the genetics of a seed's embryo, which are the result of contributions from both parents. Here we focus on how maternal effects and embryo genetics affect seed dormancy in crop–wild hybrid sunflowers (Helianthus annuus). Using three laboratory experiments, we quantified the germination and dormancy of 15 crop–wild hybrid sunflower cross types, while also identifying achene characteristics that may influence the differential germination observed. We found that increased frequencies of crop alleles and the maternal effects imparted by hybridization can reduce dormancy, though the effect of increased frequencies of crop alleles was more pronounced in wild- and F1-produced than in the crop-produced achenes. The more open pericarp of the crop-produced achenes and the shorter relative distance that their radicles had to travel to germinate may explain some of the observed maternal effects. Finally, we generated hypotheses about how these results could affect survival and crop gene introgression in the field.

Leontopodium is a genus of approximately 30 species with a conspicuous Asian–European disjunct distribution. In this study samples from the Himalayan/Tibetan centre of diversity of the genus, as well as from Europe, were analysed to infer a phylogeny of the genus using sequences of nuclear ribosomal (ITS and ETS) and plastid (matK and trnL/F) DNA. The Southeast Tibetan monotypic Sinoleontopodium [Leontopodium lingianum (Y.L.Chen) Dickoré, comb. nov.] falls into Leontopodium. Monophyly of Leontopodium, including Sinoleontopodium, is supported. Due to low rates of sequence divergence, intrageneric relationships in general are weakly supported, a pattern frequently observed in plant groups centred in the Tibetan Plateau. Three phylogenetic groups can be identified, however, and these are also supported by morphology. The low levels of nucleotide divergence suggest a young age for the group, which has been influenced by the turbulent geological history of the Tibetan Plateau. Leontopodium is a characteristic Sino-Himalayan element that appears to have found its way into the mountains of Europe in geologically recent times. The two European taxa, Leontopodium alpinum and L. nivale, form a genetically distinct group, which, considering the wide geographic disjunction, shows surprisingly little divergence from its Asian relatives.

In temperate plant communities, seed size is often inversely related to seed longevity at the species level. We tested if the inverse relationship between seed size and seed longevity holds among individuals within populations of Ambrosia trifida L. (Asteraceae), a summer annual agricultural weed in the eastern United States Corn Belt that typically emerges in two successive flushes: one before 1 May and one after 1 May. The effects of maternal phenotype on seed morphology, seed weight, late emergence (emergence after 1 May) and seed-bank persistence were determined in two 1-year experiments. All seeds were collected from individuals at weekly intervals for 3 weeks. Sixty seeds per collection were used in the analysis. Despite fluctuating environmental conditions during seed development, seed weight within maternal families remained constant for different maturation times. Differences among families constituted 69% of total variation in seed weight, whereas differences within maternal families composed 31% of the variation in seed weight. Percentage late emergence and percentage seed-bank persistence varied among maternal families. In four maternal families, either 0% or 100% of seedlings emerged after 1 May, but a majority of other maternal families produced seedlings both before and after 1 May. Seed-bank persistence rates ranged from 1 to 51% among maternal families. Percentage late emergence and percentage seed-bank persistence were inversely related to maternal-family mean seed weight in 2006, but not in 2005. These results suggest that the inverse relationship between seed size and seed longevity occurs among individuals of a population, but is affected by the environment.

The effects of maternal air temperature and soil moisture upon seed physiological dormancy (PD) alleviation of an Australian native Asteraceae were investigated. From the onset of flowering, Actinobole uliginosum plants growing ex situ were subjected to either a warm (mean 26°C) or cool (mean 17°C) temperature regime, with adequate or limited water availability. In the warm environment, the reproductive phase was accelerated, and plants yielded fewer seeds over a shorter, earlier harvest period, when compared to those in the cool environment. Initial germination of all seeds was low ( < 20% at 15°C) due to PD, which was gradually alleviated by a dry after-ripening (DAR) treatment (34/20°C, 40% relative humidity, in darkness). Seeds from plants grown in the warm environment were more responsive to DAR than seeds from the cool environment, but maternal plant water availability had little effect on dormancy status. Germination was higher at 15°C than at 25/15°C, reaching a plateau of c. 80% germination after 20 weeks DAR. Before DAR, application of GA3 had little impact on seeds, which would consequently be classified as having deep PD if tested at the time of dispersal. However, DAR caused seeds to become increasingly responsive to GA3, reaching 97% germination at 15°C following just 4 weeks of DAR, which would indicate non-deep PD if seeds were tested following a period of warm, dry storage. Maternal air temperature regulates PD status of A. uliginosum, such that seeds collected from a warmer environment are likely to be more responsive to DAR. Post-harvest storage in an environment suitable for DAR affects seed response to GA3, which has implications for germination stimulation and dormancy classification.

Seeds of the narrow-endemic Solidago shortii and of the geographically-widespread S. altissima and S. nemoralis collected and buried in 1992 and 1993 were incubated in light and in darkness at 15/6°, 20/10°, 25/15°, 30/15° or 35/20°C following various periods of burial in soil in a non-temperature-controlled glasshouse. At maturity in November, seeds of the three species germinated to 0–1% in light at 15/6°C and to 10–77% at 20/10°, 25/15°, 30/15° and 35/20°C. Seeds exhumed each April from 1993 to 1996 and incubated in light at 15/6° and 20/10°C germinated to ≥83% and ≥90%, respectively, whereas those exhumed each September of 1993–96 germinated to ≤2%and ≤40%, respectively. At 25/15°, 30/15° and 35/20°C in light, seeds of S. altissima and S. shortii germinated to ≥52% and those of S. nemoralis to ≥19/, regardless of when they were exhumed. Timson's index, which integrates percentages, rates and times for onset of germination, was higher at all temperature regimes for seeds exhumed in April 1995 than for those exhumed in September 1995. Freshly-matured seeds of the three species germinated to 0–11% in darkness. Furthermore, regardless of when they were exhumed, seeds of S. altissima and S. nemoralis incubated in darkness germinated mostly to only 0–9% over the range of temperature regimes. In contrast, ≤88% and ≤6% of the seeds of S. shortii exhumed and incubated in darkness each April and September of 1993–96, respectively, germinated, ≤1% of them germinating while buried in soil. Thus, although buried seeds of all three species exhibited an annual conditional dormancy/non-dormancy cycle, only those of S. shortii exhibited cyclic changes in their germination response in darkness.

The effect of dry storage under ambient laboratory conditions on after-ripening and survivorship was tested on seeds of the geographically-widespread Solidago altissima and S. nemoralis and the narrow-endemic S. shortii. Freshly-matured seeds of S. altissima collected in 1991 and in 1992 germinated to low or moderate percentages in light at 15/6, 20/10 and 25/15°C and to high percentages at 30/15 and 35/20°C, whereas those of S. nemoralis and S. shortii germinated to low percentages over the range of temperature regimes. After 0.8–1.8 years of storage, 1991 seeds of S. altissima incubated in light germinated to high percentages at 25/15, 30/15 and 35/20°C, those of S. nemoralis did so at 30/15 and 35/20°C and those of S. shortii at 20/10, 25/15, 30/15 and 35/20°C; 1992 seeds of all three species germinated to high percentages at 20/10, 25/15, 30/15 and 35/20°C. Freshly-matured 1991 and 1992 seeds of the three species germinated to low percentages in darkness over the range of temperature regimes, and only seeds of S. shortii germinated to high percentages after 0.8–1.8 years of storage. Compared with cold stratification, dry storage was only moderately effective in breaking dormancy in these three species. The primary difference in after-ripening of seeds of the three species was that seeds of the narrow endemic germinated to higher percentages in darkness than those of its two geographically-widespread congeners. Survivorship curves for 1991 and 1992 seeds of S. altissima and S. nemoralis and for 1992 seeds of S. shortii were of Deevey Type I; the survivorship curve for 1991 seeds of S. shortii was closest to Type II. Longevity of 1991 seeds of S. altissima, 1992 seeds of S. nemoralis and 1991 and 1992 seeds of S. shortii was <4.0 years, whereas that of 1991 seeds of S. nemoralis was <2.3 years; 5% of 1992 seeds of S. altissima were viable after 4.0 years.

Seeds of the geographically-widespread Solidago altissima and S. nemoralis and the narrow-endemic S. shortii were buried in pots of soil and placed in a glasshouse without temperature control. After 0.3–4.3 years of burial, some seeds (21–60%) of all three species were viable and they germinated to 75–100% during 2 weeks of incubation in light at 30/15°C. Soil samples collected from several population sites of S. altissima, S. nemoralis and S. shortii were placed in the glasshouse and monitored for seedling emergence. During the first, second, third, fourth, fifth and sixth springs, the number of S. altissima seedlings m−2 emerging was 108–1080, 8–494, 0–520, 0–69, 0–6 and 3, respectively, of S. nemoralis was 108–1122, 17–667, 0–42, 0–6, 0, 0 and 0, respectively, and of S. shortii was 61–1753, 0–25, 0–6, 0, 0 and 0, respectively. More seedlings emerged from disturbed than from non-disturbed soil, but the differences were not significant. Thus, although some seeds of all three species buried in pots remained viable in soil throughout the 4.3-year burial period, longevity was greater and size of seed bank larger in field-collected soil samples containing seeds of the geographically-widespread species than in those containing seeds of the narrow endemic. Although 34 studies have reported seeds of 17 species of Solidago present in soil seed banks, the present study is the first to show, conclusively that Solidago can form a persistent seed bank.