The studies concerned the variability in nectar and pollen production in flowers of 75 double-low lines of white mustard (Sinapis alba L.) and a reference cultivar ‘Nakielska’. Also, rates of insect visitation to flowers in 19 lines were investigated. Significant genotypic differences were found in nectar amount, sugar concentration in nectar and total nectar sugar amount. The average nectar amount/10 flowers varied from 2.3 to 24.4 mg, with a mean 14.7 mg for ‘Nakielska’. Nectar concentration for most lines exceeded 20%. The majority (52%) of the lines tested produced more than 2 mg of sugars/10 flowers in nectar. The average amounts of pollen varied from 1.2 to 12.0 mg/10 flowers, with the mean 8.5 mg for ‘Nakielska’. No clear genotypic effect on the amount of pollen/10 flowers was demonstrated. The lines did not differed significantly in their attractiveness to flower visitors. The main foragers were honey bees (93% of all visiting insects). It is concluded that the double-low lines of S. alba are comparable to conventional cultivars in their potential for nectar flow but perform poorer as pollen producers. The studies concerned the variability in nectar and pollen production in flowers of 75 double-low lines of white mustard (Sinapis alba L.) and a reference cultivar ‘Nakielska’. Also, rates of insect visitation to flowers in 19 lines were investigated. Significant genotypic differences were found in nectar amount, sugar concentration in nectar and total nectar sugar amount. The average nectar amount/10 flowers varied from 2.3 to 24.4 mg, with a mean 14.7 mg for ‘Nakielska’. Nectar concentration for most lines exceeded 20%. The majority (52%) of the lines tested produced more than 2 mg of sugars/10 flowers in nectar. The average amounts of pollen varied from 1.2 to 12.0 mg/10 flowers, with the mean 8.5 mg for ‘Nakielska’. No clear genotypic effect on the amount of pollen/10 flowers was demonstrated. The lines did not differed significantly in their attractiveness to flower visitors. The main foragers were honey bees (93% of all visiting insects). It is concluded that the double-low lines of S. alba are comparable to conventional cultivars in their potential for nectar flow but perform poorer as pollen producers.
In the years 2007-2008, the flowering biology of Malus sargentii, an ornamental apple tree native to Japan, was studied in the conditions of Lublin (Poland). The daily rate of flower opening, flowering duration and flower visitation by insects were determined. The amount of nectar produced per flower and sugar content in the nectar were investigated. The size of nectaries and the micromorphology of their surface were examined using light and scanning electron microscopy. It was found that the greatest amount of flowers opened between 11.00 and 13.00. During this time, the largest number of insects was observed in the flowers. Bees (90%) were predominant among the insects, with a much smaller number of bumblebees (6%) and butterflies (4%). The flower life span was 5 days. Over this period, the flower produced, on the average, 0.71 mg of nectar with an average sugar content of 32%. The nectaries of Malus sargentii are orange-yellow coloured and they represent the hypanthial type. Due to the protrusion of the nectariferous tissue, they are classified as automorphic nectaries. The surface of the epidermal cells of the nectary was distinguished by distinct cuticle folds. A small number of stomata were located only in the basal part of the nectary. At the beginning of flowering, all stomata were closed, but secretion traces were observed near well-developed outer cuticular ledges.
Flowering phenology, diurnal dynamics of blooming, insect visitation and pollen production in Aconitum lycoctonum L. and Aconitum carmichaelii Debeaux were investigated in 2012–2013 in the Lublin area, SE Poland. Flowering of A. lycoctonum occurred in June/July, whereas A. carmichaelii bloomed in September/October. Both Aconitum species differed in terms of the diurnal pattern of flowering. The flowers of A. lycoctonum started opening at 5.00, whereas those of A. carmichaelii started blooming at 8.00 (GMT+2h). The species differed in the number of anthers per flower, the size of anthers, and the mass of pollen produced in anthers. As a result, the flowers of A. lycoctonum produced less pollen (mean = 1.0 mg per 10 flowers) than the flowers of A. carmichaelii (mean = 8.2 mg per 10 flowers). The estimated pollen yield was 0.2 g per m2 for A. lycoctonum and 1.6 g per m2 for A. carmichaelii. The flowers of both Aconitum species were foraged exclusively by bumblebees with the predominance of the long-tongued Bombus hortorum. Nectar was a more attractive floral reward than pollen. The propagation of Aconitum lycoctonum and A. carmichaelii in ornamental gardens may support the conservation of bumblebees whose populations are steadily declining.
In the years 2004-2006, flowering dynamics and nectar secretion of Phacelia campanularia A. Gray flowers as well as the insect visitation rate were studied in the climatic conditions of Lublin, Poland. The flowering of phacelia started in the middle of June and lasted for 1.5 up to 2 months. Full bloom occurred between the third and fifth week of the flowering period of this taxon. For the study period, the average weight of nectar produced by 10 flowers was 75.64 mg, weight of sugars 11.31 mg, while their concentration in the nectar was 20.2%. Among the entomofauna foraging on the flowers of phacelia, honey bees were predominant, with their proportion among the pollinators accounting for 84.8%.
Knowledge of the flowering phase and plant pollination ecology is very important for understanding the life history of long-lived perennials. In the case of rare species, the information may have implications for conservation practices. Our studies on flower morphology and blooming biology of the vulnerable plant Senecio macrophyllus M. BIEB. were conducted in situ (flowering, activity of insect visitors) in the largest population in SE Poland and in laboratory (light and scanning electron microscopy). The disc florets open diurnally with most intensive anthesis in the early afternoon and attract insect visitors with nectar and pollen. In highly protandrous disc florets, pollen viability decreases in time, whereas stigma receptivity increases. The upper part of the pistil forms a brush-like pollen presenter, covered with unicellular trichomes with chromoplasts. Pollen presentation lasts 4–11 hours per floret, and 8 days in a single head, the main function of which is to extend the availability of male gamets for reproduction. The number of florets per head, the head size, and the number of pollen grains produced per anther, and the pollen grain viability differed significantly between microsites. The finding indicates that, apart from the biotic factors, abiotic conditions may considerably influence generative reproduction of the species. In the study area, the principal visitors of S. macrophyllus flowers were Hymenoptera, with predominance of Apis mellifera (53.4% of visits). The remarkable share of butterflies (13.9%) recognized as the long-distance moving insects may improve the genetic variability of individuals within a fragmented population. A more detailed study is necessary to explain the role of insect visitors in effective pollination and in gene transfer between patches. The assessment of optimal conditions for the generative reproduction is fundamental for the in situ conservation of this rare species.
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