Chemotactic behavior of Chlamydomonas reinhardtii is altered during the sexual life cycle. Unlike vegetative cells and noncompetent pregametes, mature gametes did not show chemotaxis to ammonium. Loss of chemotaxis to ammonium in mating-competent cells is controlled by gamete-specific genes that are common for both mating-type gametes. Change of chemotaxis mode requires the sequential action of the two environmental signals: removal of ammonium from the medium and light. The mutants lrg1, lrg3, and lrg4 affected in the light-dependent step of sexual differentiation exhibited the loss of chemotaxis to ammonium in the absence of light. These data indicate that there are common components in the signaling pathways that control change of chemotactic behavior and forming of mating competence in gametes.

Aim: Create a method for highly sensitive, selective, rapid and easy-to-use detection and identification of economically significant potato pathogens, including viruses, bacteria and oomycetes, be it single pathogen, or a range of various pathogens occurring simultaneously. Methods and Results: Test-systems for real-time PCR, operating in the unified amplification regime, have been developed for Phytophthora infestans, Pectobacterium atrosepticum, Dickeya dianthicola, Dickeya solani, Ralstonia solanacearum, Pectobacterium carotovorum, Clavibacter michiganensis subsp. sepedonicus, potato viruses Y (ordinary and necrotic forms as well as indiscriminative test system, detecting all forms), A, X, S, M, potato leaf roll virus, potato mop top virus and potato spindle tuber viroid. The test-systems (including polymerase and revertase) were immobilized and lyophilized in miniature microreactors (1Á2 ll) on silicon DNA/RNA microarrays (micromatrices) to be used with a mobile AriaDNA â amplifier. Conclusions: Preloaded 30-reaction micromatrices having shelf life of 3 and 6 months (for RNA-and DNA-based pathogens, respectively) at room temperature with no special conditions were successfully tested on both reference and field samples in comparison with traditional ELISA and microbiological methods, showing perfect performance and sensitivity (1 pg). Significance and Impact of the Study: The accurate, rapid and user-friendly diagnostic system in a micromatrix format may significantly contribute to pathogen screening and phytopathological studies.

Viral and bacterial diseases of potato cause significant yield loss worldwide. The current data on the occurrence of these diseases in Russia do not provide comprehensive understanding of the phytosanitary situation. Diagnostic systems based on disposable stationary open qPCR micromatrices intended for the detection of eight viral and seven bacterial/oomycetal potato diseases have been used for wide-scale screening of target pathogens to estimate their occurrence in 11 regions of Russia and to assess suitability of the technology for high-throughput diagnostics under conditions of field laboratories. Analysis of 1025 leaf and 725 tuber samples confirmed the earlier reported data on the dominance of potato viruses Y, S, and M in most regions of European Russia, as well as relatively high incidences of Clavibacter michiganensis subsp. sepedonicus, Pectobacterium atrosepticum, and P. carotovorum subsp. carotovorum, and provided detailed information on the phytosanitary status of selected regions and geographical spread of individual pathogens. Information on the occurrence of mixed infections, including their composition, was the first data set of this kind for Russia. The study is the first large-scale screening of a wide range of potato pathogens conducted in network mode using unified methodology and standardized qPCR micromatrices. The data represent valuable information for plant pathologists and potato producers and indicate the high potential of the combined use of matrix PCR technology and network approaches to data collection and analysis with the view to rapidly and accurately assess the prevalence of certain pathogens, as well as the phytosanitary state of large territories.

Fungal diseases of plants are of great economic importance causing 70–80% of crop losses associated with microbial plant pathogens. Advanced on-site disease diagnostics is very important to maximize crop productivity. In this study, diagnostic systems have been developed for simultaneous detection and identification of six fungal pathogens using 48-well microarrays (micromatrices) for qPCR. All oligonucleotide sets were tested for their specificity using 59 strains of target and non-target species. Detection limit of the developed test systems varied from 0.6 to 43.5 pg of DNA depending on target species with reproducibility within 0.3−0.7% (standard deviation). Diagnostic efficiency of test systems with stabilized and freeze-dried PCR master-mixes did not significantly differ from that of freshly prepared microarrays, though detection limit increased. Validation of test systems on 30 field samples of potato plants showed perfect correspondence with the results of morphological identification of pathogens. Due to the simplicity of the analysis and the automated data interpretation, the developed microarrays have good potential for on-site use by technician-level personnel, as well as for high-throughput monitoring of fungal potato pathogens.

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