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The investigation of dormancy release in Aesculus hippocastanum seeds was aimed at estimating the proportion of coat-imposed to embryo dormancy, and studying the growth initiation providing embryo dormancy release. During winter, horse chestnut seeds exhibited 16–17 week-lasting deep dormancy, which predominantly was determined by coat-imposed dormancy. Embryo dormancy lasted for 11–12 weeks of wet cold stratification. Embryo dormancy was weak, even the embryo axes excised from deeply dormant seeds were capable of extending to the size exceeding the axis length in intact seeds at radicle protrusion. Embryo dormancy release manifested itself in gradually increasing growth capacity of both embryo axes and cotyledonary petioles. The growth initiation in horse chestnut seeds occurs only by cell elongation. During growth initiation, a more rapid fresh weight gain was observed in comparison with length increment, thus indicating that accumulation of osmotically active substances and active water uptake by embryo axis cells were ahead of their increasing longitudinal cell wall extensibility. Cell wall loosening appeared to be directly related to embryo dormancy release. The hormonal regulation of embryo dormancy release in horse chestnut seeds is discussed.
Extract of Polyscias filicifolia suspension culture was used to reduce damage to horse chestnut (Aesculus hippocastanum) leaves by larvae of the horse chestnut leaf miner (Cameraria ohridella). The results showed the repellent effect of biomass extracts on Cameraria ohridella moths. The number of moths caught per day on sticky traps treated with extract was more than 50% lower than the control. The same extract on leaflets caused C. ohridella females to lay ~20% fewer eggs than on leaflets without extract. P. filicifolia extract had a repellent effect on female moths in laboratory conditions as well. Only single mines were observed on leaves treated with P. filicifolia extract, five times less than on control leaves. The data indicate that P. filicifolia extract can be used as a repellent for C. ohridella in springtime when the overwintering generation emerges from pupae.
We explored changes in growth, phenology, net CO₂ assimilation rate, water use efficiency, secondary defense compounds, substrate and foliage nutrient concentration of a degraded urban horse chestnut (Aesculus hippocastanum L.) site restored for three years using mulching (tree branches including foliage) and fertilization (primarily nitrogen addition). Prior to restoration, this site was characterized by high pH (ca. 8), low foliage and substrate N, and high Na and Cl concentration. Our data indicated that in untreated plots NaCl used for road deicing is the decisive factors that may be responsible for the decrease of foliar N concentration (via a reduction in NO₃⁻ uptake), for the decrease in photosynthesis (through high concentrations of Na and Cl in the leaves) and for increased senescence of the leaves. After three years of treatment, total nitrogen concentration in substrate increased by 3- to 4-fold and calcium concentration decreased by more than 50% in relation to pretreatment levels. Treatment significantly increased seed production (from less than 12 to more than 100 seeds per tree), individual leaf mass (from 1.8 to 3.3 g/leaf), CO₂ assimilation rate (by 21 to 30 %), improved leaf C:N ratio, and increased foliage life span by as much as six weeks. The beginning of leaf fall in untreated control trees started in midJuly and those of mulched and fertilized trees in late October. Applied treatment also eliminated visible symptoms of leaf damage due to high sodium and chlorine levels, indicating the possible role of other factors in the development of necroses. After three years of treatment, pH of most degraded plots declined from 8.2 to 7.8. That decline was accompanied by an increase in foliar Zn, Cu, and Pb concentration in the mulched and fertilized plants. In addition, treatment lowered foliage phenolics making these plants potentially more vulnerable to insect herbivory. Our study indicates that stable carbon isotope discrimination is of little value as an indicator of cumulative salinity and urban environment stress in A. hippocastanum due to pronounced differences in leaf phenology and ontogeny. The results of our study show that street tree recovery can take as little as two to three years after application of fertilization and mulching.
The horse chestnut leaf miner, Cameraria ohridella Deschka & Dimic (Lepidoptera: Gracillariidae), is a new invasive pest that has spread all over the Europe over the last 25 years. This paper presents research aimed to: 1) compare the effectiveness of sticky pheromone traps of various types (sizes and colors), 2) determine the effect of a trap location on moth catches. Studies were conducted in Warsaw and Falenty near Warsaw. No trap color preference by male moths was found in tests of white, blue and green barrier traps. Barrier traps had the largest sticky area (32 dm2) in comparison to PL-2 (5.625 dm2) and delta PL-1 (3.4 dm2) traps, thus they caught the highest total number of males, however PL-2 traps were the most effective (268-381 moths/dm2). The results of the studies suggest that to make traps with the C. ohridella pheromone be more effective they should: a) be located on a stem below a tree crown or in its lower part for the first C. ohridella generation, and in crowns for the second and later insect generations, b) be placed in some distance from a tree stem, if located in crowns.
The survey on spreading of Erysiphe flexuosa (Peck) U. Braun & Takamatsu (syn. Uncinula flexuosa Peck) was performed on horse chestnuts in different locations in Wielkopolska and Kujawsko-Pomorskie provinces. It was stated that powdery mildew occurred commonly on trees. In comparison to 2008 more infected by E. flexuosa chestnuts were found in 2009. The percentage of white chestnuts (Aesculus hippocastanum) with the disease increased from 1.1% in 2008 to 19.4% in 2009. The infection level of pink chestnuts (A. xcarnea) was similar in both years (69.2 and 66.1%).
In the light of contemporary issues of urban development and the natural environment deterioration, a research concerning taxonomic diversity and the state of dendroflora preservation are the basis for any further activities in the fields of shaping and preservation of urban green areas.
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