The growing importance of forest plantations increases the demand for phytopathogen resistant forest trees. This study describes an effective method for early detection and identification of the main fungal phytopathogens in planting material of silver birch (Betula pendula) and downy birch (B. pubescens), based on the estimation of the size of the internal transcribed spacers (ITS1 and ITS2) in the 18S-5.8S-28S rDNA gene cluster, which are species-specific for most micromycetes. The electrophoretic assay of the ITS1 and ITS2 loci has allowed us to identify predominant phytopathogenic fungal species in downy and silver birch in planta. This new molecular genetic method can be used to screen birch and other forest trees for different fungal pathogens to evaluate disease resistance. This information can be useful in breeding new genotypes of forest trees, including transgenic clones with modified wood composition.
Different pines species are heavily infected with fungal pathogens all over the world, some of them are alien species for European region. The potential invasion of alien species into forests, forest nurseries, urban greeneries causes great concern among Belarusian phytopathologists. In this regard, in recent years local scientists have been monitoring the phytosanitary state of natural and managed plantations to identify alien species. The aim of this investigation was to monitor the phytosanitary state of conifers in botanical and dendrological gardens, urban plantations and tree nurseries in the Republic of Belarus, and assessment of the incidence of alien pathogens of pines. There were used light microscopy and molecular genetic techniques. As a result of our research the brown spot needle blight fungus, Mycosphaerella dearnessii was for the first time noted in the region of the Republic of Belarus in a consignment of imported plants of pines Pinus mugo, Pinus nigra, Pinus ponderosa. The disease was revealed both on young and adult plants in botanical gardens and nurseries. In the forests, urban greeneries Mycosphaerella dearnessii is currently not identified. The fungus affects not only the old, but also young needles, strongly inhibiting the growth of trees. Based on the investigation results we suppose that this disease can be dangerous for pinetums in our country.
Curly birch [Betula pendula var. carelica (Merckl.) Hämet-Ahti] is a relatively rare variety of silver birch (B. pendula Roth) that occurs mainly in Northern Europe and northwest part of Russia (Karelia). It is famous for the beautiful decorative texture of wood. Abnormal xylogenesis underlying this trait is heritable, but its genetic mechanism has not yet been fully understood. The high number of potentially informative genetic markers can be identified through sequencing nuclear and organelle genomes. Here, the de novo assembly, complete nucleotide sequence, and annotation of the chloroplast genome (plastome) of curly birch are presented for the first time. The complete plastome length is 160,523 bp. It contains 82 genes encoding structural and enzymatic proteins, 37 transfer RNAs (tRNAs), and eight ribosomal RNAs (rRNAs). The chloroplast DNA (cpDNA) is AT-rich containing 31.5% of A and 32.5% of T nucleotides. The GC-rich regions represent inverted repeats IR1 and IR2 containing genes of rRNAs (5S, 4.5S, 23S, and 16S) and tRNAs (trnV, trnI, and trnA). A high content of GC was found in rRNA (55.2%) and tRNA (53.2%) genes, but only 37.0% in protein-coding genes. In total, 384 microsatellite or simple sequence repeat (SSR) loci were found, mostly with mononucleotide motifs (92% of all loci) and predominantly A or T motifs (94% of all mononucleotide motifs). Comparative analysis of cpDNA in different plant species revealed high structural and functional conservatism in organization of the angiosperm plastomes, while the level of differences depends on the phylogenetic relationship. The structural and functional organization of plastome in curly birch was similar to cpDNA in other species of woody plants. Finally, the identified cpDNA sequence variation will allow to develop useful genetic markers.
A system for vector control of current in the circuit of a polyphase electric machine has been developed. For this, on the basis of the analysis of electromagnetic processes in a multiphase semiconductor converter of electrical energy, its discrete mathematical model was created, which takes into account the redistribution of electromagnetic energy by individual spatial harmonic components depending on the number of phases. Using this mathematical model and the scheme of injection of higher current harmonics, which provides a polyharmonic mode of operation of a semiconductor converter, a method for independent control of the spatial harmonic components of the input current of the converter has been developed. The formation in each of the phases of polyharmonic currents, conjugated in shape and phase with the voltage supplying the converter, is carried out by means of control actions in the form of voltage vectors of a semiconductor switch, the implementation of which is carried out by the method of multiphase space-vector modulation. To check the developed provisions, a simulation model of a nine-phase semiconductor converter of electrical energy with a vector control system was created. The results of the study of the model confirmed the adequacy of the developed technical solutions, the use of which will ensure the most complete realization of the own advantages of a multiphase electric machine in order to generally improve the weight, size and energy indicators of the autonomous power supply system.
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