A Study on Petal Morphological and Physiological Characteristics of Styrax japonicus during the Flowering Period

Styrax japonicus is a small ornamental tree with medicinal values, although its flowering period is short. To date, information about the morphological and physiological characteristics of the petals during the flowering period is limited. In this study, we observed the structure of the petals at the full flowering stage with a scanning electron microscope and detected the contents of nutrients, minerals, and endogenous hormones and the activities of enzymes at different flowering stages. The results showed that the content of soluble sugar exhibited an ‘increase-decrease’ trend, whereas the contents of soluble protein, nitrogen (N), phosphorus (P), and abscisic acid (ABA) showed a ‘decrease-increase’ pattern. The content of starch descended continuously, but the contents of potassium (K), gibberellic acid (GA3), indoleacetic acid (IAA), and malondialdehyde (MDA) ascended continuously. The activities of peroxidase (POD) and superoxide dismutase (SOD) first rose and then declined during the flowering period. Higher contents of soluble sugar, N, K, and IAA promoted S. japonicus flowering; meanwhile, lower contents of starch, soluble protein, P, and GA3 in addition to the lower activity of SOD might be some of the causes of the short flowering period. This work will serve as the foundation for a scientific technique to utilize the flowers and extend the flowering period in S. japonicus.

Chloroplast phylogenomics and divergence times of Lagerstroemia (Lythraceae)

Background Crape myrtles, belonging to the genus Lagerstroemia L., have beautiful paniculate inflorescences and are cultivated as important ornamental tree species for landscaping and gardening. However, the phylogenetic relationships within Lagerstroemia have remained unresolved likely caused by limited sampling and the insufficient number of informative sites used in previous studies. Results In this study, we sequenced 20 Lagerstroemia chloroplast genomes and combined with 15 existing chloroplast genomes from the genus to investigate the phylogenetic relationships and divergence times within Lagerstroemia. The phylogenetic results indicated that this genus is a monophyletic group containing four clades. Our dating analysis suggested that Lagerstroemia originated in the late Paleocene (~ 60 Ma) and started to diversify in the middle Miocene. The diversification of most species occurred during the Pleistocene. Four variable loci, trnD-trnY-trnE, rrn16-trnI, ndhF-rpl32-trnL and ycf1, were discovered in the Lagerstroemia chloroplast genomes. Conclusions The chloroplast genome information was successfully utilized for molecular characterization of diverse crape myrtle samples. Our results are valuable for the global genetic diversity assessment, conservation and utilization of Lagerstroemia.

Is the double-spined bark beetle Ips duplicatus a new threat to Picea omorika in urban habitats?

The double-spined bark beetle Ips duplicatus (Coleoptera: Curculionidae, Scolytinae) is an invasive forest pest having a broad range of coniferous hosts within Europe. We found this species to be also developing in the Serbian spruce Picea omorika. Ips duplicatus infested 14 (52%) of 27 P. omorika mature trees in an arboretum garden in northern Slovakia in Central Europe during the summer of 2019. Logs from the upper part of stems of P. omorika trees placed in eclectors in the laboratory, yielded a total of 179 individuals of three scolytine species, with prevalence of I. duplicatus. Our results show that I. duplicatus also colonized less likely host such as the Serbian spruce, causing threat to this ornamental tree and contributing to its mortality in urban habitats during hot and dry summer weather.

Botryosphaeria Dothidea and Neofusicoccum Yunnanense Causing Canker and Die-Back of Sequoiadendron Giganteum in Croatia

Sequoiadendron giganteum Lindl. [Buchholz] is a long-lived tree species endemic to the Sierra Nevada Mountains in California. Due to its massive size and beauty, S. giganteum is a popular ornamental tree planted in many parts of the world, including Europe. Since 2017, scattered branch die-back has been observed on S. giganteum trees in Zagreb, Croatia. Other symptoms included resinous branch cankers, reddish-brown discoloration of the sapwood and, in severe cases, crown die-back. Branches showing symptoms of die-back and cankers were collected from six S. giganteum trees in Zagreb and the aim of this study was to identify the causal agent of the disease. The constantly isolated fungi were identified using morphology and phylogenetic analyses based on the internal transcribed spacer (ITS) of the ribosomal DNA (rDNA), and partial sequencing of two housekeeping genes, i.e., translation elongation factor 1-α (TEF 1-α), and β tubulin 2 (TUB2). The fungi were identified as Botryosphaeria dothidea (Moug.) Ces. and De Not. and Neofusicoccum yunnanense G.Q. Li & S.F. Chen. The pathogenicity test was conducted in a plant growth chamber on S. giganteum seedlings and revealed that N. yunnanense was more aggressive compared to B. dothidea. N. yunnanense was able to reproduce symptoms of canker and die-back and kill plants seven weeks after inoculation whereas B. dothidea produced cankers. To the best of our knowledge, this is the first report of B. dothidea and N. yunnanense causing canker and die-back disease of S. giganteum in Croatia. It is also the first record on the identity and pathogenicity of any fungal species associated with S. giganteum in this country. The study expended the known host range of N. yunnanense to include S. giganteum, which is a valuable ornamental tree in Croatian landscapes. Disease management strategies should be developed to mitigate or reduce the impact of the disease.

Hibiscus tiliaceus (coast cottonwood).

H. tiliaceus is a medium-sized tree, normally 8-12 m tall (maximum 20 m) and stem to 50 cm dbh, with a dense crown and spreading branches. The bark is grey, smooth on young trees with brown, horizontally elongated lenticels; hard and thick with black, vertical fissures on larger trees. It has mucilaginous sap. The original natural distribution is obscure, but H. tiliaceus is now widely distributed in the sub-humid and humid tropics. It grows on coastal foreshores on sand or rock, behind mangrove communities that border brackish swamp forest and littoral subtropical rainforest on alluvial flats near the sea. It is infrequent on atolls. The timber is very fine and smooth, easy to work and takes a good polish. The leaves, bark and sap are used medicinally: leaves are wrapped around bone fractures; and fluid from young stems is used as an antiseptic for skin eruptions. The roots, flowers and young leaves are edible. The inner bark is used for its fibre to make twine, cordage for ropes, nets, basketware, fishing line and making skirts for ceremonial occasions. The bushy habit and decorative flowers make this species an attractive shade or ornamental tree for coastal gardens, although it is easily damaged by sea winds. It is a short-lived pioneer species that can become invasive and the extensive root system can become a problem to cultivation. It is thought to be a host for insect vectors of foliar decay disease of coconuts.

Corymbia citriodora (lemon-scented gum).

C. citriodora is a handsome tree of excellent form, with a well-shaped but sparsely foliaged crown. It is widely adaptable, drought tolerant, and capable of reasonable growth rates in both summer and winter rainfall areas. This species is one of the better eucalypts for cultivation at lower latitudes of the subtropics and tropics, but not in equatorial regions (Jacobs, 1981). It produces strong, hard and moderately durable wood suitable for fuelwood, charcoal, posts and poles, household products, tool handles, sawn timber, and general construction materials. C. citriodora is also used as a source of non-wood forest products including honey, essential oil, shade and shelter. It is a fine ornamental tree and is often planted along roadsides or in parks.

Delonix regia (flamboyant).

D. regia, with showy red flowers, is primarily planted as an ornamental tree throughout the tropics.

Cedrela odorata (Spanish cedar).

C. odorata is a large tree up to 40 m tall and 2 m in diameter which produces a light-weight timber. Its natural distribution range is confined to the New World, extending from northern Mexico to Argentina, including the Caribbean. It is widely planted throughout the tropics and its timber is well known for its use in cigar boxes and a broad range of other products, including musical instruments. It is also occasionally planted for shade and used as an ornamental tree on roadsides and in parks. C. odorata has great potential as a plantation species, due to its fast growing and timber producing characteristics. It is also used as an agroforestry species in cocoa and coffee plantations (Lemmens et al., 1995). C. odorata is highly vulnerable to attack by shoot borers (Hypsipyla spp.), whose larvae damage seedlings and saplings. There is some evidence that infestation can be controlled by planting C.odorata with other species, such as Leucaena leucocephala, Neolamarckia cadamba or (under light shade) with Eucalyptus deglupta (Lemmens et al., 1995).