Number Of Capitula Research Articles

Field assessment in land of origin of host specificity, infestation rate and impact of Ceratapion basicorne a prospective biological control agent of yellow starthistle

Yellow starthistle, Centaurea solstitialis (Asteraceae), is an important invasive alien weed in the western United States. Currently established biological control agents attack only the capitula (flowerheads), and are not effectively controlling the plant in much of its range. The geographic center of diversity for the plant appears to be in Turkey, but no agents have been introduced from this country. Ceratapion basicorne (Coleoptera: Apionidae) is common in Central Turkey, attacking 25–100% of yellow starthistle plants. In a field experiment, Ceratapion spp. attacked 90% of yellow starthistle plants and 88% of milk thistle plants (Silybum marianum) but not seven other plant species, including artichoke and safflower. We suspect that a different species of insect attacked milk thistle, but they emerged before the plants were sampled. Laboratory tests showed that C. basicorne does not oviposit in milk thistle. Ceratapion basicorne appears to be more host specific than was suggested by previous studies of a population in Italy (Clement et al. 1989. Ann. Entomol. Soc. Am. 82: 741–747). The insect is gregarious, and the number of larvae per plant was positively correlated to root diameter. The level of damage to individual plants was positively correlated to the proportion of plants attacked, indicating aggregation both among plants and within plants. Field data did not show any impact of the insect on plant size or number of capitula, but germination rate of seeds produced by infested plants was 15% lower than for uninfested plants at two of three sites studied.

Revisión de <i>Mattfeldanthus</i>, un género de Vernonieae (Asteraceae) endémico del nordeste de Brasil

Mattfeldanthus H. Rob. & R. M. King constituye uno de los pocos géneros de la tribu Vernonieae con corolas cigomorfas. Este grupo tiene dos especies endémicas del nordeste de Brasil que habitan en la “caatinga” y en campos rupestres. Las especies se pueden diferenciar entre ellas por varios caracteres morfológicos tales como la forma de sus involucros, el número de capítulos, el tamaño de las flores y la forma de los filarios. En el presente trabajo se describen e ilustran las dos especies de Mattfeldanthus. También se discuten las relaciones filogenéticas del género con otras Vernonieae y se amplía la distribución geográfica de las especies a un área mayor del nordeste de Brasil

Laboratory Trials of the Efficacy of the Crown Weevil Mortadelo horridus (Coleoptera: Curculionoidae) for the Biological Control of Slender Thistles Carduus pycnocephalus and C. tenuiflorus in Southwestern Australia

The hypothesis that larval crown weevil (Mortadelo horridus Alonso-Zarazaga and Sanchez-Ruiz) can suppress vegetative growth, seed set and viability in the winter annual slender thistles (Carduus pycnocephalus L. and C. tenuiflorus Curt.) was tested in laboratory gardens. Different densities (eight and 16) of M. horridus larvae and eggs were inoculated onto slender thistle rosettes between one and four times. Controls received no eggs or larvae. Larval feeding destroyed the apical meristems of treated plants, producing multi-crowned rosettes and significant declines in leaf area in both species, irrespective of the number of larvae. Treated thistles bolted at the same time and had a 4-fold increase in stem number compared to controls. The stems of control plants were up to one-third taller and thicker than attacked plants. Relative to controls, the leaves of treated plants had significantly fewer spines, decreased leaf area and decreased leaf perimeter, with less deeply lobed leaf margins. The total number of capitula produced by control and experimental groups was not significantly different, but consideration of fertile capitula only revealed a reduction in fertile capitula production following weevil attack. This was most marked in C. pycnocephalus. Control plants also produced significantly wider capitula. No control plants died, compared to 17 and 26% of the attacked plants of C. pycnocephalus and C. tenuiflorus, respectively. Implications for biocontrol of slender thistles are discussed.

Agrotechniques to enhance the productivity of niger (Guizotia abyssinica) under rainfed conditions

A field experiment was conducted during the rainy (kharif) season of 2012 at Dharwad, Karnataka, to study the effect of 3 sowing dates [first fortnight (FN) of July, second FN of July and 1 FN of August], 2 plant geometries (45 cm 10 cm and 60 cm 10 cm) and 2 doses of Cycocel spraying (500 ppm and 1,000 ppm at 30 days after sow- ing) on growth and yield of rainfed niger (Guizotia abyssinica Cass.). Sowing of niger in I fortnight of July at a plant geometry of 45 cm 10 cm with application of cycocel @ 1,000 ppm at 30 DAS significantly enhanced the plant height (123.5 cm), branches (21.2), dry-matter accumulation (61.2 g/plant), number of capitula (59.9/plant), 1,000- seed weight (4.22 g), seed yield (0.675 t/ha), oil yield (275 kg/ha), uptake of major nutrients (42.1, 10.2 and 14.2 kg NPK/ha), net returns ( 17,673/ha) and benefit: cost ratio (2.00).

Relationship Among Growth Attributes of Spotted Knapweed (Centaurea maculosa) in Western Montana1

Spotted knapweed is an important weed of rangeland in the northwestern United States. A study was conducted near Corvallis, MT, during 1992 to 1994 in order to assess the relationship among the growth attributes of spotted knapweed to identify a minimum set of measurable plant characteristics that are representative of spotted knapweed vigor. Spotted knapweed growth attributes that were examined included plant age, root diameter, plant height, number of stems per plant, aboveground biomass, number of capitula (seed heads) per plant, and number of capitula per stem. Spotted knapweed age was positively correlated with root diameter, number of stems per plant, aboveground biomass, and proportion of bolted plants. Most spotted knapweed plants did not bolt until the third or fourth year. Although plant age is not measured easily in the field, it may be useful as a covariate in an analysis of experiments involving plant competition or nonlethal biological control agents. Root diameter can be used as a nondestru...

Inbreeding depression under intraspecific competition in a highly outcrossing population of Crepis sancta (Asteraceae): evidence for frequency‐dependent variation

Inbreeding depression is a major selective factor acting to maintain outcrossing in hermaphroditic plants. Recently it has been shown that environmental conditions may greatly affect the levels of inbreeding depression. In this study, the effects of intraspecific competition, from either crossed or inbred progeny, and plant density on the expression of inbreeding depression were estimated for the allogamous colonizing plant Crepis sancta (Asteraceae). The population used in this experiment showed a very high outcrossing rate (t = 0.99). Inbreeding depression was measured for germination, survival to reproduction, number of capitula, and a multiplicative fitness estimate. We found that inbreeding depression on survival, the number of capitula, and total fitness was the greatest when inbred plants compete with outbred plants. The effect of density on inbreeding depression was less evident. The major implication of our study is that the relative fitness of selfed progeny is strongly influenced by the type of competitors (outbred or inbred). These results support the hypothesis that inbreeding depression varies according to the density and frequency of outbred plants and suggest that it could be considered as a density- and frequency-dependent phenomenon.

Spatio-temporal variation of reproductive success and conservation of the narrow-endemic Centaurea corymbosa (Asteraceae)

The viability of a metapopulation of the rare, cliff-dwelling Centaurea corymbosa depends critically on the persistence of extant local populations, as it has a very low colonising ability. The variation in components of seed production in space and time was investigated and compared with the variation of supposedly causal plant and population traits. Temporal variation in the number of capitula per plant and in the number of ovules per capitulum were related to resource limitation between years and flowering periods, respectively. The seed-to-ovule ratio also varied widely, because of variation in fertilization rate, and, to a lesser extent, in abortion rate; predation being negligible. Isolated individuals had lower fertilization rates than individuals within dense patches. But despite a high density, the smallest studied population showed the lowest fertilization rates and highest abortion rates. This Allee effect on seed production represents a possible threat for small and/or low-density populations. Reinforcing populations of low density and supplying the smallest populations with new genotypes, by seed deposition into clefts of rocks, are suggested as possible conservation management strategies for C. corymbosa.

Analysis of variability for seed yield and related characters in safflower (Carthamus tinctorius L.)

Thirty five genotypes of saffower are grown under four diverse environments. High genotypic coefficient of variation for yield per plant and number of seeds per capitulum was observed at all the environments and only for yield per plant over environments. Moderate coefficient of variation for number of primary branches per plant, number of secondary branches per plant, number of capitula per plant and harvest index was observed in pooled analysis. High heritability estimates were observed for days to maturity, number of capitula per plant, number of seeds per capitulum, yield per plant and hull content. Seed yield per plant, number of seeds per capitulum and harvest index had high genetic advance coupled with high heritability under individual environment, indicating scope for the improvement of these characters through selection.

Responses of Sexual and Apomictic Genotypes of Taraxacum officinale to Variation in Light

Abstract: The mode of reproduction, sexual or asexual, will influence the way populations respond to selective pressures. This can cause genetic and ecological divergence between sexual and asexual forms of the same species. Here we examine differences in morphology and phenology between sexual and apomictic types of dandelion, Taraxacum officinale. Sexual and apomictic dandelions were collected from a mixed population on the banks of the river Rhine, The Netherlands. Clonal copies of both sexual and apomictic genotypes were planted in an experimental garden under two light levels. Sexual plants flowered four days later on average than apomicts, but the number of capitula was the same. Apomicts had longer leaves and were heavier than sexual plants, especially under shaded conditions. In apomicts plasticity for leaf length and height was larger than in sexuals, but for most other measured traits no differences in plasticity were observed. Trait values of apomicts were within the same range as those of sexual plants.

Réintroduction de sphaignes dans une tourbière exploitée : Évaluation de divers moyens de protection contre la dessiccation

In order to restore peatlands after peat harvesting operations, Sphagnum diaspores were reintroduced in combination with i) physical protection devices or ii) an irrigating system. The response of five Sphagnum species (Sphagnum angustifolium [C. Jens. ex Russ.] C. Jens. in Tolf, S. magellanicum Brid., S. papillosum Lindb., S. fuscum [Schimp.] Klinggr. and S. capillifolium [Ehrh.] Hedw.) was investigated in relation to two types of peat substrates for two growing seasons. The physical protections consisting of plastic shade cloth (40% and 60% shade) improved the development of a greater number of capitula compared with control surfaces without protection or surfaces covered with a perforated polyethylene sheet. This stimulating effect could be caused by higher humidity created by a shade screen. Irrigation also enhanced the establishment success of Sphagnum but the effect was less successful than expected. During a year with normal summer climatic conditions (1993), the sphagna of the sections Cuspidata and Acutifolia established well with equal number of capitulum after 117 days of growth. In contrast, after a second year of growth which was much more humid because of abundant rainfalls, the sphagna of section Cuspidata were maintained or multiplied while those of section Acutifolia regressed. Since it is difficult to predict long-term climatic conditions, we suggest the reintroduction of a mixture of many species in order to favor the adaptation of the moss cover to diverse climatic conditions. In conclusion, we recommend the reintroduction of a variety of Sphagnum species under physical protections like plastic shade screen to favor an adequate microclimate during the restoration phase of a continuous moss carpet.

Response of Hybrid and Open‐Pollinated Safflower to Plant Population

AbstractFour safflower (Carthamus tinctorius L.) cultivars were evaluated at five plant populations in experiments over 2 yr at three North Dakota locations. Differences in achene yield due to plant population were not significant. Hybrid AGC‐353 produced significantly higher achene yield than the other cultivars. Number of capitula per plant and achenes per capitulum were the yield components most influenced by plant population. Cultivar effects were significant for all yield components. Plant population did not influence achene oil content; however, significant differences among genotypes occurred. Cultivar S‐541 and hybrid AGC‐353 produced significantly higher and lower achene oil percent, respectively, than the other cultivars. The significantly higher hull content of hybrid AGC‐353 compared with the other cultivars caused the low oil content.

Efficiency of early generation selections for yield and related characters in safflower (Carthamus tinctorius L.)

The efficiency of early generation selection for yield and related characters in safflower (Carthamus tinctorius L.) was studied in the F2, F3 and F4 generations. Twenty-five F2 progenies derived from various crosses were studied. In the F2 generation, number of capitula per plant (CNSP), number of seeds per capitulum (SPSP), test weight (SWSP), and seed yield (SYSP) were the criteria used for single plant selection. The analysis of variance showed significant differences for all of the characters in the F2, F3, and F4 generations. The analysis of variance in each of the selection classes showed highly significant genotypic differences. A large number of selections in the CNSP and SYSP classes showed greater yield than the check variety. In each class the mean for that particular character showed a positive shift. The observed F3 and F4 means for seed yield per plant was higher in SYSP, indicating the effectiveness of single plant selection for yield. Correlated response showed that selection for number of capitula per plant was effective for improvement of yield.

Effect of (2-chloroethyl) trimethylammonium chloride (CCC) on the growth, biochemistry and rubber yield of guayule plants ( Parthenium argentatum gray)

The growth retardant (2-chloroethyl) trimethylammonium chloride (CCC), supplied as a soil drench to young guayule plants (Parthenium argentatum) at doses of 250, 500 and 1000 p.p.m. (active principle), increased the following growth characteristics: plant height; length and diameter of main and secondary stems; number of leaves and leaf area, number of peduncles or main shoot of inflorescences; number of capitula per peduncle; and total dry matter. Growth activity took a long time. In addition, there was a significant increase both in the concentration of organic nitrogen in stems and leaves, and in the absolute nitrogen content in all plant organs. Leaf chlorophyll content was also higher than that seen in the control. The percentage of rubber and resin in the stems and roots was not modified by CCC, but their absolute content showed a significant increase. The stimulating action of CCC on the growth of guayule plants is discussed in terms of the higher level of nitrogen acquired by the plant.

The comparative biology of the closely related Senecio nebrodensis and S. viscosus, a narrow endemic and a widespread ruderal

The closely related Senecio nebrodensis, a perennial herb from four mountain ranges in Spain, and S. viscosus, an annual herb widespread in Europe, are being compared by the study of herbarium material and comparative cultivation. In cultivation, S. nebrodensis behaved as an annual, completing its life cycle within a shorter period of time than S. viscosus. The formation of basal leaf rosettes is much more pronounced in S. nebrodensis than in S.viscosus. The main difference between the two species, however, is their breeding system. While S. nebrodensis is self‐incompatible, S. viscosus is self‐compatible. Differences in reproductive morphology (mainly size and number of ray florets) are suggested to be related to this difference in breeding system. Despite differences in disc floret number and capitulum number observed in the cultivated material, the potential reproductive output of the two species is roughly comparable. Senecio viscosus is believed to be a descendant of S. nebrodensis. It is postulated that the former differentiated from thelatter at the latest in glacial or early postglacial times. Following postglacial climatic changes, S. nebrodensis retreated into high altitudes, while S. viscosus, adapting to these changes, expanded northwards. The strikingly different degree to which the two species exploit man‐made disturbances is interpreted as being due to a difference in opportunity: In its climatically defined range S. nebrodensis experiences little disturbance. Senecio viscosus, on the other hand, inhabits areas strongly disturbed by human activity. It is concluded that S. viscosus shows no obvious adaptations to its habitat, but is well preadapted.

Seasonal changes in response ofSenecio ovatus to grazing by the chrysomelid beetleChrysomela speciosissima

The response ofSenecio ovatus to herbivory byChrysomela speciosissima (Coleoptera, Chrysomelidae) was studied in the Krušné hory Mountains, Czechoslovakia. The following questions were addressed: (1) what is the impact of natural levels of insect herbivory on the performance of individual plants, (2) how do the levels of herbivory change during the growing period, and (3) what is the relative importance of direct and indirect effects of herbivory? Ten experimental plots sprayed with metathion and ten controls were established. Damage to plants was quantified in the period of maximum herbivore activity (June) and again at the end of the growing season (August). In the first half of the season, total leaf area in grazed ramets was reduced by 30.3% compared to ungrazed ramets; half of this reduction was due to beetle consumption and half was due to indirect effects. Individual leaf area was not significantly different between treatments. Insecticide-treated ramets were taller and heavier than the controls. During the second half of the growing period the differences in ramet weight and leaf area disappeared because of compensatory growth. However, the insecticide-treated ramets remained taller and had higher seed numbers per capitulum. Neither number of capitula per ramet nor seed weight were significantly different between treatments. In the grazed population, the leaf area reduction (30.3%) in June resulted in 36.5% reduction in fecundity at the end of August.

The effect of galls induced by the gall fly Procecidochares utilis on vegetative growth and reproductive potential of crofton weed, Ageratina adenophora

SummaryReproductive potential and vegetative growth of Ageratina adenophora (Spreng.) K. & R. (crofton weed) were measured under ambient conditions to evaluate the efficacy of the gall fly, Procecidochares utilis Stone as a biocontrol agent for this weed. Galls induced by the fly resulted in the production of underdeveloped capitula and a reduction in the number of capitula and filled achenes per capitulum. Galling had no effect on subsequent germination of the seed produced. Where vegetative growth was concerned the effect of galling ranged from a temporary cessation of growth to death of stems above the gall. Although galling promoted production of side shoots, the dry mass of above‐ground material was markedly reduced.

Effect of Soil pH, Soil Water, Light Intensity, and Temperature on Perennial Sowthistle (Sonchus arvensisL.)

Growth of perennial sowthistle was examined under different levels of soil pH, soil moisture content, light intensity, and temperature. Soil pH ranging from 5.2 to 7.2 had little effect on the number of leaves, rosette diameter, plant height, and number of capitula. However, total dry weight was 30% less in plants grown in soil of pH 5.2 compared to those grown at higher soil pH levels. Perennial sowthistle demonstrated a consistent positive growth response to increasing soil water including saturation. Severe reduction in vegetative and reproductive growth occurred in plants grown in soil below field capacity. Plants grown under full light (1015 μE m−2s−1photosynthetic photon flux density) developed a fourfold increase in the number of capitula per plant and a 50% increase in total dry weight compared to plants grown at 285 μE m−2s−1. Initiation of reproduction was delayed 4 weeks for plants grown at 580 μE m−2s−1and 285 μE m−2s−1. Plants grown under less than full light developed fewer but larger leaves. Plants grown under a day/night temperature of 20/15 C grew more rapidly than those under 30/25 C or 10/5 C. Plants at 30/25 C began to senesce 7 to 8 weeks after planting. Net carbon assimilation, leaf conductance, transpiration, and water use efficiency decreased as soil moisture and light intensity decreased. Plants at 30/25 C had the highest rate of transpiration and the lowest water use efficiency. The observed optimum for perennial sowthistle growth occurred at a soil pH of 6.2 or 7.2, water-saturated soil, high light intensity, and a temperature of 20/15 C, day/night.

Safflower susceptibility and response to feeding by grasshoppers

SUMMARYFeeding by three grasshopper species, Camnula pellucida, Melanoplus packardii and Melanoplus sanguinipes, on three safflower (Carthamus tinctorius) lines for a 6‐wk period from anthesis was monitored under field conditions. Ratings of feeding damage to different plant parts (leaves, floral parts, capitula, and peduncles) and measurements after termination of feeding (dry weight, seed yield, seed weight, seeds per capitulum, and capitula per row) were compared among grasshopper species and safflower lines.The Melanoplus species fed preferentially on leaves, floral parts, and capitula, while C. pellucida exhibited only peduncle feeding, which resulted in head clipping. Defoliation of 20 to 30% was associated with significant increases in total dry matter, seed yield, and number of capitula. Further defoliation resulted in decreases.The safflower lines differed in response to grasshopper feeding. S‐208 was most susceptible to defoliation by grasshopper feeding, exhibiting decreased dry weight, seed yield, and capitula number. Lesaf 34C‐00 was most tolerant and only M. packardii caused significant dry weight and seed yield reductions. Feeding by C. pellucida on this line resulted in an overall seed yield increase. Feeding by M. sanguinipes on Seedtec‐5 resulted in yield increases of up to 16%. It appears that certain grasshopper species can increase seed yield in some safflower lines by stimulating the production of additional capitula. Therefore, moderate populations of such grasshoppers in fields of appropriate safflower cultivars do not necessarily require control.

Rates of nitrogen supply during different developmental stages affect yield components of safflower (Carthamus tinctorius L.)

Abstract The yield components of two safflower (Carthamus tinctorius L.) lines have been studied in glasshouse experiments. Three nitrogen supply rates were used in each of three developmental phases: emergence to the beginning of stem-internode elongation, from stem elongation to when the terminal capitular bud became visible, and from then to maturity. The major component of yield was the number of capitula per plant. The successive orders of branches, primary to quarternary, are each terminated by capitula. The number of secondary capitula was determined by the nitrogen supply rates between the time of stem elongation and when the terminal bud became visible; the number of tertiary capitula by the nitrogen supply after both stem elongation and bud visibility; and the number of quaternary capitula by the nitrogen supply after terminal bud visibility. The number of filled seeds per plant was linearly correlated with the number of capitula which in turn was linearly related to the dry weights of the plants. This relationship differed between the two genotypes used: Gila and an experimental line, A1110. Total plant dry weights and nitrogen contents were positively affected by nitrogen supply rates after stem elongation, as were the separate organs: leaf laminae, stem + petioles, and roots. Single seed weights did not differ much between nitrogen supply rates, and the only significant effect of nitrogen supply on oil concentration in the seeds was a depression by the highest rate after bud visibility. The product of these yield components, oil yield per plant, was significantly affected by the nitrogen supply rates between stem elongation and bud visibility. The nitrogen concentration in seeds was only affected by nitrogen supply rates after bud visibility; there were differences in the response of the two genotypes. The results show that the most efficient time of application of nitrogen fertilizer to safflower crops is at stem elongation.

Factors affecting establishment and survival ofSoliva(Onehunga weed) at Auckland, New Zealand

Abstract In intra-specific competition in pots, high densities of Soliva caused increased mortality and also resulted in a marked reduction in the number of capitula and lateral shoots. At the highest density (5000 plants m-2) many of the plants did not produce either a central capitulum or any lateral shoots. In the field Soliva cypselas germinated a few days after the first heavy rain in late summer-early autumn. Up to 40 000 seedlings m-2 were recorded in close cut turf in Auckland. Soliva seedlings were competing intraspecifically and also against perennial grasses and other lawn weeds. Early seedling mortality substantially reduced the numbers of Soliva seedlings and subsequently the population of mature plants declined more slowly during the season. Plants did not survive the summer even when watered. In turves where the associated species, which were mainly perennial, were left uncut from October to May the canopy height increased to 150–200 mm and at the end of the 7 month period there were almost no Soliva plants present. Cut turves had high numbers of seedlings and young plants in proportions roughly similar to the original population densities. However, a greater number of cypselas were recovered from the uncut plots and a high proportion of the cypselas may have remained dormant when under a canopy. Soliva is a vigorous competitor in short turf and, indeed, requires either a manged turf or open areas for survival.