Effects of foliar applied gibberellic acid and benzyladenine upon yield components in sunflower (Helianthus annuus L.)

Sunflower yield is determined by seed number/m^–2 and by achene weight. Frequently, a high percentage of empty achenes in the inner portion of the capitulum, probably due to a reduced vascularization of that section of the flower head, decreases final yield. The objective of the present research is to determine if foliarly applied gibberellic acid (GA) and benzyladenine (BA) can enhance the vascularization in the inner portion of the capitulum, improving photoassimilate translocation. Field experiments were conducted during 1989/90 with hybrid SPS 894 and during 1990/91 with hybrid ACA 882. GA (150 mg/l^–1), BA (150 and 250 mg/l^–1) and GA 150+BA 150 mg/l^–1 each were foliarly applied 20, 40, or 60 days after emergence. For both seasons and hybrids plant growth regulator (PGRs) applications significantly reduced the percentage of empty achenes, increased achene weight, achene weight (× 1000) and achene number in the inner portion of the capitulum and in the middle and outer portion during 1990/91. A 25% increase in seed yield was achieved due to PGR application and the capitulum partition index (achene weight/receptacle weight^–1, CPI) was significantly increased due to an improvement in photoassimilate distribution. A distribution model was derived showing that preferential allocation of photoassimilates in the outer portion of the capitulum can be modified by PGR application, demonstrating that photoassimilate distribution is under hormonal control.Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET)     

Influence of achene heteromorphism on life-cycle traits in the annual weed gallant soldier (Galinsoga parviflora Cav.)

Galinsoga parviflora (gallant soldier), Asteraceae, produces two morphologically distinct achenes in a single capitulum: peripheral and central. The morphological, phenological and generative reproduction traits of the progeny derived from peripheral and central achenes that were cultivated in greenhouse conditions were analyzed. Differences between the progeny of various morph types were manifested at different stages of life. The plants of both morph types developed at a similar rate and they entered key phenological phases at the same time except for the flowering stage. The average height of the studied plants was similar on the same days of the experiment. The study showed that plants from peripheral achenes realize the generative reproduction in other pattern than plants from central achenes. The plants from central achenes produce more capitula per plant at the beginning of the fruiting stage, whereas plants from peripheral seeds achieve the highest number of capitula per plant at later stages. Finally, on day 130 of the experiment, the number of capitula per plant of both morphs equalized. At the early fruiting stage, the number of achenes per capitulum of plants from the two morphs did not differ significantly. The number of achenes within one capitulum decreases with plant age in both populations, but the rate of that decline is greater in the progeny of peripheral seeds. The number of peripheral achenes per capitulum in plants from both achene types decreases at a comparable rate. In contrast, the number of central achenes is reduced at a faster rate in plants germinated from peripheral achenes. After day 83, the individuals from peripheral diaspores intensified their reproductive effort; they produced more capitula but with fewer number of achenes than in individuals from central diaspores. On day 130, the number of dispores per plant of the two morphs equalized. The changes of fecundity of peripheral and central progeny with the age of the plant (at different stages of the life cycle of a single plant) contribute to an intensive seed rain throughout the fruiting period. By producing a large number of less fertile capitula with a stable number of peripheral achenes, plants derived from peripheral achenes are able to supply a higher share of peripheral achenes than if they would produce fewer but more fertile capitula. This strategy increases the pool of peripheral achenes.     

Ecology of achene dimorphism in Leontodon saxatilis

BACKGROUND [corrected] AND AIMS: Leontodon saxatilis produces two morphologically distinct achenes (morphs) in a single capitulum: one row of dark brown achenes without a pappus lies at the edge ('peripheral achenes'; 0.74 +/- 0.18 mg) while the inner ones are light brown with a pappus ('central achenes'; 0.38 +/- 0.07 mg). The hypothesis that achene heteromorphism in L. saxatilis widens its ecological amplitude was tested. KEY RESULTS: Achenes of both morphs germinated over the same range of temperatures (6-33 degrees C) but the central achenes showed significantly higher germination percentages, and the two also differed significantly in their annual dormancy cycle, with the peripheral achenes showing greater dormancy for part of the year. Seedlings from the two morphs did not differ significantly in total biomass after 2 and 4 weeks of growth, neither did they differ significantly in root and shoot weight and root:shoot ratio. Plants from both morphs growing at different regimes of soil moisture, nutrients and competition did not differ significantly in their number of achenes per capitulum. While the number of central achenes varied, that of peripheral achenes remained constant at approx. 13. Drier soil led to an increase in the number of central achenes in plants from both morphs. CONCLUSIONS: The peripheral achenes can replace the mother plant in the following growing season, whereas the central achenes are well adapted for wind dispersal and thus for colonization of new sites. However, the extent of variation in germination characteristics was similar to that found in seed populations of homomorphic plants, which suggests that germination percentage and other growth characteristics do not contribute to widening the ecological amplitude. The habitat of most heteromorphic species, the morphs of which differ greatly in germination and/or growth characteristic, are deserts or highly disturbed areas where such differences are highly advantageous, but in the moderate habitat of L. saxatilis the differences may prove a disadvantage.     

一年生短命植物疏齿千里光果实异形性的生态学意义

疏齿千里光(Senecio subdentatus)是分布在新疆北部古尔班通古特沙漠中的一种具异形瘦果的菊科一年生短命植物。将野外观测与室内实验相结合, 对该物种异形瘦果的形态、扩散和萌发特性, 以及异形瘦果产量与植株大小的关系进行了研究, 并对其生态学意义进行了探讨。结果表明: 疏齿千里光果序中的外围果和中央果均为柱形, 但前者为淡黄色, 后者为褐色, 且二者在大小、冠毛长度及果皮微形态等方面均存在明显差异。两种瘦果均以单个果实为扩散单元, 且在静止空气中的降落速度和在1 m·s^-1与2 m·s^-1风速下的扩散距离无显著差异, 说明虽然果实大小和冠毛长度对瘦果扩散具有不同的影响, 但对其整体扩散能力无明显影响。在各温变周期(5/2、15/2、20/10、25/15和30/15 ℃)处理中, 淡黄色外围果的萌发率均高于褐色中央果的, 且不同温度间两种瘦果的萌发率均存在显著差异, 但光照条件对其无显著影响。果序中的中央瘦果数明显多于外围果的, 且植株中外围果所占比例与植株大小间呈显著负相关关系, 而中央果所占比例与植株大小间呈显著正相关关系。这些特点说明, 该物种的小植株倾向于产生较多较易萌发的外围果, 大植株倾向于产生较多不易萌发的中央果。在古尔班通古特沙漠不可预测的极端环境中, 疏齿千里光可通过异形瘦果间的萌发差异及调节其不同大小植株中异形瘦果的比例, 来减少同胞后代之间的竞争, 增加其对不同微环境条件的生态适应性。     

Significance of achene characteristics and within-achene resource allocation in the germination strategy of tetraploid Aster pilosus var. pilosus (Asteraceae)

The interrelationships among achene weight, allocation to embryo and pericarp, and germination time were determined for 500 stratified achenes of tetraploid Aster pilosus Willd. var. pilosus. Only 52.6% of the achenes germinated. Germinated achenes were significantly heavier than ungerminated achenes. Germination time was independent of achene weight and embryo weight, but varied inversely with pericarp weight. Variable achene weight is evolutionarily advantageous. Heavy achenes are at an advantage in that their proportionately larger embryos and thinner pericarps facilitate germination, promoting competitive establishment of seedlings. Lighter achenes are also at an advantage through increased dispersibility, and their relatively thick pericarp provides a persistent seed bank. Evolutionary pressures presumably maintain the variability in achene weight of var. pilosus. These results are discussed in the context of the early midsuccessional ecology of var. pilosus.     

Genetic components of heterocarpy inMicroseris hybrid B87 (Asteraceae,Lactuceae)

Microseris B87 is derived from a single hybrid specimen betweenM. pygmaea with few, weakly hairy peripheral achenes and aM. bigelovii with many, strongly hairy peripheral achenes. Offspring through the F4 and F5 generations obtained by spontaneous selfing were analyzed for the segregation of quantitative and qualitative characters relating to achene dimorphism. The phenotypic effects of two previously identified unlinked genes determining the relative number of outer achenes are characterized in partially and completely homozygous sublines. We show that two morphological markers genetically linked to one of these genes are themselves regulated by the system inducing heterocarpy. Not more than two more unlinked genes are involved in the genetic basis of the heterocarpic response. The interaction of these genes in determining the heterocarpy phenotypes is discussed in the framework of a model postulating genes for a morphogen gradient across the capitulum and genes responding to this gradient.     

Effect of source–sink ratio on seed set and filling in sunflower (Helianthus annuus L.)

Poor seed development in sunflower may result from insufficient assimilate supply (source limitation). To test this hypothesis, the effects of changed source–sink ratio on seed set (measured as percentage of empty achenes) and seed filling (measured as dry mass per filled achene) in individual plants were investigated. Source–sink ratio, defined as leaf area per floret (LAF), was experimentally altered using invasive (floret removal, defoliation) and non‐invasive (pulse of chilling, short days or shading during leaf or floret initiation) treatments. Shading at floret initiation proved the most effective non‐invasive method. Generally, an increase, or decrease, in LAF improved, or impaired, both seed set and filling. Increasing LAF by 2.0 cm²[95% confidence interval (1.5, 2.5)] decreased the percentage of empty achenes by 36.9%‐points (?41.9, ?30.9) and increased dry mass per filled achene by 20.1 mg (13.6, 26.7) in the capitulum centre. The effect of source–sink ratio on seed set was always strongest in the centre, whereas peripheral whorls were not affected. Achene mass was affected in all parts of the capitulum. It is concluded that source limitation is a major cause for empty achenes in sunflower plants grown under non‐stress conditions.     

Ecological correlates of achene mass variation in Chrysothamnus nauseosus (Asteraceae)

Chrysothamnus nauseosus (Asteraceae) is a complex polymorphic shrub species widely distributed in western North America. In a study of 86 populations belonging to 15 subspecies, achene mass varied among populations over a sevenfold range. Achene mass was closely correlated with capitulum size at the subspecies level, varied little between wild-growing and common-garden-grown members of a population, and was under strong genetic control. Subspecies with the heaviest achenes are restricted to specialized edaphic environments (dunes and badlands) or late seral montane riparian communities, while subspecies that are widely distributed and that occur in early seral habitats have less heavy achenes. Selection on achene mass has apparently been a notable feature of the adaptive radiation of Chrysothamnus nauseosus into the wide array of habitats it currently occupies. Within a wild population, achene mass was greater for plants fruiting in midautumn than for plants fruiting early or late in the autumn, and this same trend was observed within individual plants in garden populations, indicating environmental control, perhaps through resource limitation. Highly significant between-plant differences in achene mass were found in both wild and garden populations, suggesting that within-population genetic variation is sufficient to permit continuing selection.     

Reproductive biological characteristics potentially contributed to invasiveness in an alien invasive plant Bidens frondosa

Bidens frondosa L. (Asteraceae) is a widespread invasive weed in China. By experimental observation and bagging treatment, the reproductive biological characteristics of this species, such as phenology of flowering, floral syndrome, breeding system and seed germination characteristics, were studied to assess the association of these reproductive characteristics with invasiveness. Flowers of B. frondosa bloom from September to October every year in Ji'an city, Jiangxi province. The lifespan of a single capitulum is approximately 4 to 5 days, with 30 to 60 florets per capitulum. The capitulum diameter, anthocaulus length, floret length and width, stamen length and pistil length were 6.1, 30.9, 2.2, 0.6, 3.0 and 2.7 mm, respectively. The seed set percentage of 48.5% in the treatment of bagging flowers without emasculation suggests B. frondosa is self‐compatible; meanwhile, the percentage of 63.1% in the treatment of bagging with emasculation and manual xenogamy suggests it also is cross‐compatible. P/O ratio per capitulum of this species was 450.5, which suggests that the breeding system of B. frondosa is facultative xenogamous, and it needs pollinators to some degree. The main floral visitors were insects of Hymenoptera, Diptera and Lepidoptera. The 1000‐achenes weight was 1.97 g. The achenes emerged as a small germination peak from the fourth to fifth day, and had a high accumulated germination rate of up to 84.0% on day 20 after sowing. Our experimental findings suggested that the reproductive biological characteristics, such as the versatile mating system of self‐ and cross‐pollination, high seed production, a special method of achene dispersal and germination peak, accompanied by a high accumulated germination rate, might contribute to the invasive ability of B. frondosa.     

菊科入侵植物三叶鬼针草的繁殖特征及其与入侵性的关系

三叶鬼针草(Bidens pilosa)是一种危害严重的菊科入侵植物.通过实验观察和人工控制套袋等方法,对其花序开花动态、花粉胚珠比(P/O)、自交亲和性、花粉活力、访花昆虫和种子(瘦果)的萌发率等与繁殖相关的特征进行了研究,探讨了这些繁殖特征与入侵性的关系.三叶鬼针草在10-11月开花,单个花序的花期约为5-6天.每小花的花柱基部有圆筒状的蜜腺环绕.单个花序内可自交亲和,自交结实率和花粉活力均较高,其P/O值为1754.12士29.87.主要访花者为灰蝶科(Lycaenidae)、粉蝶科(Pjerjdae)和茧蜂科(Braconidae)昆虫.三叶鬼针草所具有的灵活交配机制是其入侵成功的重要因素.此外,三叶鬼针草结实量大、种子产生迅速且适于传播,以及种子萌发范围广和短期快速萌发等特性也增强了其入侵性.     

Polyamines in normal and auxin-induced strawberry fruit development

The possible involvement of polyamines during strawberry ( Fragaria × ananassa Duch.) fruit development was investigated. Putrescine, spermidine, and spermine were identified in strawberry receptacles and achenes at all stages of development. Total (free) polyamine levels decreased from a maximum of 485 nmol g⁻¹ fresh weight at pollination to a minimum of 55 nmol g⁻¹ fresh weight in ripe receptacles. Total polyamine concentrations during corresponding stages of development were consistently higher in achenes than in receptacles, and ranged from 891 to 203 nmol g⁻¹ fresh weight. Removal of achenes from the surface of developing receptacles 10 days after pollination reduced receptacle growth, and re-initiation of growth by application of 1 m M α-naphtaleneacetic acid (α-NAA) was accompanied by a rapid increase in polyamine concentrations 24 h after treatment. Polyamine content per receptacle increased >3-fold in normally developing receptacles and in de-achened, auxin-treated receptacles 10 days after removal of achenes, but did not increase during this period in de-achened receptacles not treated with exogenous auxin. α-NAA increased growth and polyamine levels to a greater extent than the structurally related, but less effective auxin, β-NAA. Polyamine concentrations in receptacles with intact achenes remained similar to those of auxin depleted (de-achened) receptacles, implying that the concentration of these compounds may not be limiting following achene removal.     

Variability and Cryptic Heteromorphism of Ambrosia artemisiifolia Seeds: What Consequences for its Invasion in France?

BACKGROUND AND AIMS: Ambrosia artemisiifolia is a ruderal weed introduced from North America to Europe. It produces large amount of achenes which are highly heterogeneous in size. Due to the preponderant role of propagules in invasive plant processes, the achene mass variability related to germination, dispersal strategy and life history traits of offspring were investigated within this species. METHODS: The variability in achene mass was quantified among six populations sampled in different habitats. The effects of achene mass variation on germination were studied. The percentages of floating and non-floating achenes were evaluated in the studied populations. The consequences of floatability on the growth and traits of the offspring were studied. KEY RESULTS: Mean achene mass ranged from 1.72 to 3.60 mg, depending on the populations, and was highly variable. Variation among achenes within plants accounted for 63.9 % of the variance, whereas variances among plants within each population (22.2 %) and among populations (13.9 %) were lower. Achene masses were also positively correlated to the total germination percentage for four populations out of six. Two kinds of achenes were distinguished: floating and non-floating. The majority of floating achenes (90 %) sank 24 h after water immersion. Whatever the population, floating achenes were lighter, more dormant and germinated faster than non-floating achenes. Plants which issued from floating achenes had better growth than those from non-floating achenes. CONCLUSIONS: The capacity of A. artemisiifolia to be invasive in Europe appears to be high, possibly due to its huge plasticity in seed mass which may help it to cope with a wide range of conditions and to establish in disturbed habitats. Furthermore, the recent invasion of southern France by A. artemisiifolia could be partially explained by water dispersal of achenes through rivers and has pinpointed its colonization potential along French rivers.     

Polyamines in normal and auxin-induced strawberry fruit development

The possible involvement of polyamines during strawberry ( Fragaria x ananassa Duch.) fruit development was investigated. Putrescine, spermidine, and spermine were identified in strawberry receptacles and achenes at all stages of development. Total (free) polyamine levels decreased from a maximum of 485 nmol g⁻¹ fresh weight at pollination to a minimum of 55 nmol g⁻¹ fresh weight in ripe receptacles. Total polyamine concentrations during corresponding stages of development were consistently higher in achenes than in receptacles, and ranged from 891 to 203 nmol g⁻¹ fresh weight. Removal of achenes from the surface of developing receptacles 10 days after pollination reduced receptacle growth, and re-initiation of growth by application of 1 m M α-naphtaleneacetic acid (α-NAA) was accompanied by a rapid increase in polyamine concentrations 24 h after treatment. Polyamine content per receptacle increased >3-fold in normally developing receptacles and in de-achened, auxin-treated receptacles 10 days after removal of achenes, but did not increase during this period in de-achened receptacles not treated with exogenous auxin. α-NAA increased growth and polyamine levels to a greater extent than the structurally related, but less effective auxin, β-NAA. Polyamine concentrations in receptacles with intact achenes remained similar to those of auxin depleted (de-achened) receptacles, implying that the concentration of these compounds may not be limiting following achene removal.     

The role of pollination in the population biology of the monocarpic species Cirsium palustre and Cirsium vulgare

Summary The absence of cross-pollination in Cirsium palustre and Cirsium vulgare resulted in reduced achene production while the achenes produced were heavier than those produced after cross-pollimation. Establishment of plants from non-cross-pollinated achenes is comparatively higher, facilitating the founding of a population from isolated individuals in these wind-dispersed species.If achene weight is the result of a balance between cross-pollination and self-pollination (and/or apomixis), the first causing more and thereby lighter achenes to develop, increasing density of flowering individuals in a population may lower achene weight and consequently seedling survival. This may account for the frequently observed decline of populations of fugitive monocarpic perennials.Publication of the Meijendel-comité, Nieuwe Serie no. 58     

Role of within-individual variation in capitulum size and achene mass in the adaptation of the annual Centaurea eriophora to varying water supply in a Mediterranean environment

To clarify the adaptive value of variation in capitulum size and achene mass, plants of Centaurea eriophora were studied in a glasshouse and in a natural population. C. eriophora plants consist of a basal leaf rosette from which an erect stem grows, with lateral branches of various orders ending in capitula of different orders. Primary, secondary and tertiary capitula are comparable in size and they produce similar numbers of achenes, which are similar in weight (large achenes). These capitula are formed during April, May and early June, and constitute the normal or primary flowering. Following ripening of tertiary capitula, leaves senesce, but, later during June and the first half of July, a secondary flowering of a variable number of smaller capitula may occur if wet conditions persist for longer than usual. Plants that have almost senesced develop small lateral branches 1-2 cm long bearing a few small leaves and ending in a capitulum about half the diameter of capitula from the primary flowering period. The number of achenes produced in these capitula (small achenes) and their weight are 70 and 30% less, respectively, than those of capitula formed during primary flowering. These reductions appear to result from restricted availability of resources. Large and small achenes have similar dispersal characteristics and possess similar germination potential. However, large achenes produce seedlings that are capable of emerging from greater burial depths, providing the resulting plants with a potential advantage. The normal flowering period coincides with the optimum time of year for flowering and fruiting in the south of Spain, and only if rainfall lasts longer than usual does secondary flowering occur. Secondary flowering extends the normal flowering and fruiting periods, thereby providing a supplementary crop of smaller, yet viable, fruits. It can be considered to be an adaptive response to the unpredictable Mediterranean climate, optimizing the use of available resources.     

菊科入侵植物三叶鬼针草的繁殖特征及其与入侵性的关系

三叶鬼针草(Bidens pilosa)是一种危害严重的菊科入侵植物。通过实验观察和人工控制套袋等方法, 对其花序开花动态、花粉胚珠比 (P/O)、自交亲和性、花粉活力、访花昆虫和种子 (瘦果)的萌发率等与繁殖相关的特征进行了研究, 探讨了这些繁殖特征与入侵性的关系。三叶鬼针草在10-11月开花, 单个花序的花期约为5-6天。每小花的花柱基部有圆筒状的蜜腺环绕。单个花序内可自交亲和, 自交结实率和花粉活力均较高, 其P/O值为1 7 54.1 2±29 .8 7。主要访花者为灰蝶科(Lycaenidae)、粉蝶科(Pieridae)和茧蜂科(Braconidae)昆虫。三叶鬼针草所具有的灵活交配机制是其入侵成功的重要因素。此外, 三叶鬼针草结实量大、种子产生迅速且适于传播, 以及种子萌发范围广和短期快速萌发等特性也增强了其入侵性。     

Germination requirements and dispersal timing in two heterocarpic weedy asteraceae

In SW Spain the winter annuals Anacyclus radiatus and Chrysanthemum coronarium (Asteraceae) are found as weeds in diverse crops. Both plant species are heterocarpic, i.e. the peripheral and central achenes of the capitulum are morphologically distinctive. In heterocarpic and heterospermic species the different fruit or seed morphs usually have differential ecological behaviour. In this work we have studied the morphometry, germination and dispersal timing of t he different achene morphs in A. radiatus and C. coronarium. Laboratory germination tests were carried out to evaluate the influence of incubation temperature (light/dark, 27/27, 24/18, 20/10, 15/5, 10/4 degrees C), chilling period (0, 1, 7, 21 and 60 days at 2 degrees C), GA3, nitrate and the dark on the germination percentage and rate (t50). The peripheral achenes of A. radiatus have a significantly broader wing than the central achenes. In this species, germination was inhibited in the dark but viable achenes of both types germinated completely under light exposure irrespective of test conditions. Nevertheless, the peripheral achenes germinated significantly faster compared to the central achenes (t5o 1.04 vs. 1.55 days at 24/18 degrees C). In C. coronarium peripheral achenes have three-winged ribs and are significantly longer, wider and thicker than the central achenes, which have only one- or two-winged ribs. In this species the peripheral achenes showed a much lower germination compared to the central achenes under all conditions tested (0.3-3.5% vs. 41.5-58.0%). Embryos isolated from the pericarp of peripheral achenes germinated quickly in a great extent, and when placed in close contact with a pericarp fragment they did not show any inhibition of germination, suggesting physical dormancy. To determine differences in dispersal timing between achene morphs, we monitored dispersal in a stand of both plant species. In A. radiatus the peripheral achenes were shed first, at the onset of the rainy season in late summer, whereas the central achenes dispersed from late summer to early winter. In contrast, in C. coronarium the central achenes were shed first, from early summer to early autumn, whereas the peripheral achenes dispersed mainly in early autumn. Thus, in both weed species the more dispersible and readier-to-germinate achene morph is dispersed first. The differences in the germination and dispersal behaviour between achene morphs represent an opportunistic, mixed strategy which is favourable under environmental uncertainty, and should be accounted for in order to understand the population dynamics of both weed species.     

Role of mucilage during achene germination and sprout growth of the endangered Tibetan medicinal herb Mirabilis himalaica (Nyctaginaceae) exposed to abiotic stresses

Aim Mirabilis himalaica (Nyctaginaceae) is an endangered medicinal plant mainly distributed in the plateau region of northern Tibet, China. The outer surface of M. himalaica achenes is covered by a pectinaceous mucilaginous layer upon hydration. However, the role of the achene mucilage is poorly understood. In this study, we investigated the effects of mucilage on achene germination and sprout growth under abiotic stress to explain how M. himalaica survive the alpine environment.Methods We investigated the effect of mucilage on achenes germination by contrast the capacity of water absorption, dehydration and respiration of intact achene and the achene with mucilage removal. We performed abiotic stresses experiments including drought stress, salt stress, cold stress and high temperature stress, and quantified the effects of mucilage removal on achene germination rate, root and shoot lengths of seedlings.Important findings Mucilage is extremely hydrophilic, and the mass of intact achenes can be 9-fold greater than that of demucilaged achenes. The removal of the mucilaginous layer did not significantly change final germination percentages under ideal conditions, but intact achenes (i.e. with mucilage) took longer to germinate. The mucilage significantly decreased seed respiration rates by acting as a physical barrier that prevented oxygen diffusion. Germination rates, shoot and root growth of intact achenes were higher than those of demucilaged ones during exposures to cold, heat, osmotic and salt stresses. Achene mucilage presumably plays an ecologically important role in the life cycle of M. himalaica by aiding the critical achene germination and early seedling growth in the stressful habitats of the plateau region of northern Tibet.     

Effects of nitrogen supply on growth, yield and yield components of safflower and sunflower

Safflower (Carthamus tinctorius L.) represents an important oil crop internationally and may have a certain production potential under low input conditions, particularly in organic farming systems, where the putatively low nutrient requirement would be an advantage. However, little is known about the nutrient requirements of safflower. This study was undertaken to determine the growth and yield response of safflower as compared to sunflower (Helianthus annuus L.) under different N supplies. Safflower and sunflower plants were grown in Mitscherlich pots containing equal volumes of sand, nutrient-poor limed soil, and perlite. Nitrogen supply was the same for both species (0.25, 0.5, 1.0, 1.5, and 2.0 g per pot) in the first year, but was raised for sunflower (0.5, 1.0, 2.0, 3.0, and 4.0 g per pot) in the second. Increased N supply enhanced plant growth and yield for both species. Growth and yield of safflower increased up to 1.0 g pot⁻¹, while the optimum for sunflower was 2.0 g pot⁻¹. Safflower out-yielded sunflower at low N supply, while at high N level the opposite occurred. Functional analysis according to Michaelis–Menten revealed that – in terms of yield formation – safflower is superior to sunflower under N-limited conditions. Safflower is generally more efficient than sunflower in concentrating N in their shoots. N concentration in the photosynthetically active youngest mature blade of both species exhibited the same functional relationship with the N supply, but safflower required a much lower leaf N concentration to produce optimal yield as compared to sunflower, indicating the higher efficiency of the former in terms of NUE. Yield components analysis revealed that in safflower, yield is tightly correlated with the number of capitula per plant and the mass per achene, both being strongly correlated, too. On the contrary, sunflower yield was merely determined by the number of achenes per capitulum, followed by the mass per achene. Path coefficient analysis showed that in safflower, the direct effects of the achene and leaf N content as well as the leaf dry matter on oil yield are small, and mediated principally via indirect effects on the number of achenes per capitulum, while for sunflower the number of achenes per capitulum exerts a strong direct effect. Dedicated to the late Prof. Dr. Burkhard Sattelmacher, who passed away on November 21, 2005.     

Dormancy and dispersal in dimorphic achenes of tansy ragwort,Senecio jacobaea L. (Compositae)

Summary Marginal and central florets of the capitula of tansy ragwort Senecio jacobaea yield different kinds of fruit. The central (disk) achenes are lighter (x±SE=199±5g), more numerous (x±SE=58±0.6 achenes per head), and are equipped with a pappus aiding wind transport and rows of trichomes aiding animal transport. The marginal (ray) achenes are heavier (x±SE=286±7g), less numerous (virtually invariant at 13 achenes per head), and lack dispersal structures. Whereas disk achenes are relased shortly after they mature, ray achenes are retained by the parent for a period of months following maturity.Germination at constant temperature (20°C) and with alternating light (12 h light: 12 h dark) demonstrated that disk and ray achenes exhibit different germination syndromes. Germination percentage increases linearly with achene fresh weight in both types; for a given weight, disk achenes have a higher germination percentage than ray achenes. Germination time decreases with increasing achene weight in disk achenes, but increases with achene weight in ray achenes.The germination percentages and germination times for disk and ray achenes diverge progressively with increasing achene weight. The divergence in behavior is a result of diverging patterns of dry matter allocation in the two achene types. Increase in the size of disk achenes favors the embryo fraction, thereby speeding germination while reducing protection. Increase in the size of the ray achenes favors the pericarp fraction, thereby increasing protection while delaying germination.Reduced germination percentage and germination speed of the ray achenes were shown by experimental manipulation to be caused by physical inhibition by their thicker pericarps.Dimorphism in ragwort likely speards germination out in space and time, thereby increasing the number of safe sites an individual parent can exploit in disseminating offspring. The syndrome in other heteromorphic composites resembles that of ragwort, generally combining reduced dispersal-delayed germination in the outer achenes and distance dispersal-quick germination in the central achenes. The outer achenes are generally less numerous and larger. Dispersal traits (large numbers, early release and light wieght) are the direct opposite of dormancy traits (small numbers, delayed release and heavier weight). Thus conflicts between the properties determining dormancy and dispersal appear to require separate dormancy and dispersal phenotypes.