Seed Production of Red Clover (Trifolium pratense L.) under Danish Field Conditions

High and stable seed yield is critical for red clover (Trifolium pratense L.) seed production and the commercial exploitation of the crop. A three-year experiment was conducted from 2013 to 2015 under Danish field conditions to explore the influence of precipitation during peak flowering on the seed yield of three red clover cultivars. We investigated the flowering duration and intensity based on a visual scale assessment, seed yield, and thousand seed weight in all three experimental years. In 2014 and 2015 we measured the seed yield components of floret number per flower head, seed number per flower head, and seed set. During the experimental period, high seed yields of more than 1000 kg ha−1 were obtained for the diploid cultivars ‘Rajah’ and ‘Suez’. Although a relatively high seed yield of 500 kg ha−1 was obtained in the tetraploid cultivar ‘Amos’, this was only around half of the seed yield and seed set of the diploid cultivars. Precipitation during peak flowering positively influenced the seed yield and thousand seed weight for the three cultivars. We conclude that observations of flowering phenology are required to determine the impact of environmental conditions on seed yield in red clover cultivars. Further, adequate water supply during peak flowering is important to obtain the high seed yield of red clover.

Yield and Chemical Composition of Raw Material from Meadow Arnica (Arnica chamissonis Less.) Depending on Soil Conditions and Nitrogen Fertilization

Considering the global tendency towards using valuable secondary metabolites of plant origin, there is a need to optimize the cultivation of herbal plants, e.g., the meadow arnica (A. chamissonis Less.). The inflorescences of this species (Arnicae anthodium) have a similar chemical composition and pharmacological activity to that in the mountain arnica (Arnica montana L.), and can be cultivated more easily than the mountain arnica. Therefore this study assesses soil and fertilization effects on the flower head yield and concentrations of active substances (sesquiterpene lactones, flavonoids, and essential oil) with great importance for application in the pharmaceutical and cosmetic industries. A field experiment was carried out during 2017–2019 on two types of soil (sandy and loamy soils) differing in the pH values, organic matter content, and the P, K, and Mg levels. Five levels of nitrogen fertilization were applied in both soil variants: 0, 30, 60, 90, and 120 kg N∙ha−1. The study showed that both the soil type and the nitrogen fertilization had a positive impact on the raw material yield and the content and yield of the main active substances. The cultivation of arnica in the loamy soil was more favorable—it provided a higher flower head yield, higher levels of sesquiterpene lactones, flavonoids, and essential oils, and consequently, a higher yield of these metabolites. High flower head yields were achieved at doses of 60 and 90 kg N∙ha−1. The content of sesquiterpene lactones and essential oils increased in the consecutive study years along with the increase in nitrogen doses. The highest content of flavonoids was detected in flower heads obtained from three-year-old plants fertilized with 60 kg N∙ha−1. High yields of sesquiterpene lactones and essential oils were obtained at doses of 90–120 kg N∙ha−1, whereas the fertilization with 60–90 N∙ha−1 ensured a high yield of flavonoids. The yields of sesquiterpene lactones and essential oil did not depend on their concentration but correlated with the increase in the yield of flower heads of plants cultivated in both sandy and loamy soil variants. In turn, the yield of flavonoids was influenced by both their concentration and the flower head yield. The flower head yield, the content of sesquiterpene lactones, flavonoids, and essential oils, and the yields of metabolites presented in this study indicate favorable climatic conditions for the cultivation of A. chamissonis in Central and Eastern Poland. This proves that a wide range of pharmacologically active substances can be produced in this region of Europe.

Pollination and Plant Reproductive Success of Two Ploidy Levels in Red Clover (Trifolium pratense L.)

Plant reproduction in red clover requires cross-fertilization via insect pollination. However, the influences of visitation rate and timing on maximizing ovule utilization are yet to be determined. We aimed to study the influences of visitation rate, flowering stage, and self-incompatibility on reproductive success. We applied hand and honey bee pollination in the study of eight red clover cultivars with two ploidy levels released between 1964 and 2001. In hand pollination, increasing the visitation rates (from 10 to 80 pollinated florets per flower head) increased the seed number per flower head but reduced the seed number per pollinated floret. Different flowering stages (early, middle, and full flowering) did not influence the seed number per pollinated floret significantly. There was a marked difference in reproductive success depending on the ploidy level, with 0.52 seeds per pollinated floret in diploid and 0.16 in tetraploid cultivars. During the cultivar release history, seed number per pollinated floret seemed to decrease in diploid cultivars, whereas it increased in tetraploids. In honey bee pollination, diploid cultivars had more two-seeded florets than tetraploids. Different visitation rates and the stochastic nature of pollen transfer resulted in difficulties when the plant reproductive success between hand and bee pollination was compared. A maximum of 0.27 seeds per pollinated floret were produced in hand pollination compared to the 0.34 in honey bee pollination. In spite of this, hand pollination provided a valuable method for studying the pollination biology and reproduction of red clover. Future studies may employ hand pollination to unravel further aspects of the low reproductive success with the future perspective of improving seed number per pollinated floret in tetraploid red clover.

The Influence of Flower Head Order and Gibberellic Acid Treatment on the Hydroxycinnamic Acid and Luteolin Derivatives Content in Globe Artichoke Cultivars

Flower head orders and the use of GA3 (gibberellic acid) treatment could be two influencing factors determining the bioactive compound levels in artichoke, but little to no information is available about their effects. In this study, we have therefore evaluated the influence of these factors on the hydroxycinnamic acid and luteolin derivative levels in three categories of artichoke: Seed-propagated open-pollinated cultivars; vegetatively propagated cultivars; and seed-propagated hybrids. The hydroxycinnamic acids and luteolin derivatives were quantified by RP-HPLC-DAD. The average flower head weight was the lowest in tertiary heads and GA3-treated artichokes, followed by secondary and main heads. Moreover, the hydroxycinnamic acid and luteolin derivatives levels were significantly higher in tertiary heads than in secondary or main heads. In addition, the GA3 treatment significantly reduced the hydroxycinnamic acid content and, in contrast, improved luteolin derivatives levels. These effects depended on the flower head order and cultivar. Knowledge of the effects of flower head order and GA3 treatment is therefore key in order to achieve the greatest health-benefits from artichoke consumption.

Effect of Colour of Light on Rooting Cuttings and Subsequent Growth of Chrysanthemum (Chrysanthemum × grandiflorum Ramat./Kitam.)

A closed system for plant production with artificial light is an innovative method of plant cultivation. The objective of this study was to investigate the effect of light colour on rooting cuttings and subsequent growth of chrysanthemum (Chrysanthemum × grandiflorum Ramat./Kitam.) During the experiments, the following conditions were maintained: photoperiod 16 h or 10 h, temperature 22 °C, relative humidity of 65–70%. LED lamps emitted the following light colours: white, blue, white + blue (50:50), and red + blue (75:25). For all light spectra, the photosynthetic photon flux density (PPFD) was 50 μmol m−2 s−1. The effectiveness of exposure to different light colours was measured with parameters: cutting weight (g), cutting length (cm), length of roots, and index of leaf greenness (SPAD). The measurements referred to plant features determining plant quality, i.e., the number of flower buds and flower head, the diameter of the flower head, height of plants, index of leaf greenness (SPAD), the number of leaves, and the fresh and dry weights of aboveground parts of plants. The rooting of cuttings and subsequent growth are integral processes in the cultivation of potted chrysanthemums. Both were differently affected by the colour of light from LED lamps. The exposure to red + blue light resulted in the highest leaf greenness index (SPAD) value and the shortest cuttings with the longest roots. White + blue light significantly influenced most of the growth parameters, except the height of the plants and the number of leaves.

Fruiting Season, Flowering and Peel Characteristics of Leucaena spp. Analytical Study (B)

During the flowering seasons the species varied greatly and the seasons were seldom repeated (August-October) with only three species and two species (April-June), which means that they continued throughout the months of the year. Three colours of the flower were observed in total with gradient within these three colours distributed to the studied species. In terms of the colour of the peel, two colours were distinguished only in favour of the brown-gray colour, while the forms of cracks on the outer peel surface were divided into three forms. On the other hand, each type was independent when examining the colour of the inner peel. The shape of the cross section of the branch exceeded 81.8% for the circular shape on the angular shape, while two types of branch thickness were recorded and exactly the same for texture. It was possible to observe two forms of branching of the flower-bearing branches, which were very similar to those of the two forms (non-branching and branching) with a large difference between the two forms of the flower's apex, at a rate of 20 times the round shape and 90.9% of the shape of the flower. Two flowers shoots growing types were observed named (Auxotelic and an Anauxotelic). Three main colours, white, yellow and pink were distinguished and the flower head diameter varied widely between (6.5-30 mm). Flowers season seems to be in all of the year. Outer peel thickness also varied from thick to thin to intermediate. Three forms of peel fissures were found and 54.5% to mid-brown colour. Inner peel colour can be a good item to be a key of classification of this tree. Correlation coefficient between peel thickness and outer peel colour was 0.935.

Intraspecific morphological variation of Bellidiastrum michelii (Asteraceae) along a 1,155 m elevation gradient in the Tatra Mountains

Plant species that inhabit large elevation gradients in mountain regions are exposed to different environmental conditions. These different conditions may influence plant morphology via plastic responses and/or via genetic adaptation to the local environment. In this study, morphological variation was examined for Bellidiastrum michelii Cass. (Asteraceae) plants growing along a 1,155 m elevation gradient in the Tatra Mountains in Central Europe. The aim was to contribute to gaining a better understanding of within-species morphological variation in a mountain species across elevation gradients. Twelve morphological traits, which were measured for 340 plants collected from 34 sites, were plotted against elevation using Generalised Additive Models. Significant variation in B. michelii morphology was found across the elevation gradient. Plant size, in the form of plant height, total aboveground mass and total leaf mass, decreased significantly with increasing elevation. Similarly, floral traits, such as flower head mass, total flower mass, individual flower mass, flower head diameter and ligulate and tubular flower length, also decreased significantly with increasing elevation. However, the changes in these floral traits were not as large as those observed for plant size traits. Interestingly, the number of flowers produced by the plant, both ligulate and tubular, did not change across the studied elevation gradient. In this study, elevation was found to be an important gradient across which significant intraspecific morphological variation occurred in a mountain plant. These morphological changes may have occurred in response to various abiotic and biotic factors that change along elevation gradients.

Extreme Drought Affects Visitation and Seed Set in a Plant Species in the Central Chilean Andes Heavily Dependent on Hummingbird Pollination

Rising temperatures and increasing drought in Mediterranean-type climate areas are expected to affect plant–pollinator interactions, especially in plant species with specialised pollination. Central Chile experienced a mega drought between 2010 and 2020 which reached an extreme in the austral summer of 2019–2020. Based on intensive pollinator sampling and floral studies we show that the subalpine form of Mutisia subulata (Asteraceae) is a specialised hummingbird-pollinated species. In a two-year study which included the severest drought year, we quantified visitation frequency, flower-head density, flower-head visitation rates, two measures of floral longevity, nectar characteristics and seed set and monitored climatic variables to detect direct and indirect climate-related effects on pollinator visitation. Flower-head density, nectar standing crop and seed set were significantly reduced in the severest drought year while nectar concentration increased. The best model to explain visitation frequency included flower-head density, relative humidity, temperature, and nectar standing crop with highly significant effects of the first three variables. Results for flower-head density suggest hummingbirds were able to associate visual signals with reduced resource availability and/or were less abundant. The negative effect of lower relative humidity suggests the birds were able to perceive differences in nectar concentration. Reduced seed set per flower-head together with the availability of far fewer ovules in the 2019–2020 austral summer would have resulted in a major reduction in seed set. Longer and more intense droughts in this century could threaten local population persistence in M. subulata.