Plant Pathology Science

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The importance of plant protection in modern agriculture increases as crop yields and concerns about production quality rise. Plant protection should be sufficiently effective, affordable and considerate of the environment. The integration of biological and chemical control has a potential for success because of a possible synergistic effects. It is necessary to look for organisms suitable for use in biological control, and in order to study the mechanisms of their action and the optimal conditions for incorporating such agents in plant protection and integrated management systems. One of such microorganisms is PythiumoligandrumDrechslerthatbelongs to the phylumOomycetes. This soil-resident saprophytic microorganism can be parasitic and hyperparasitic on many fungi within the same or other classes. The antagonistic activity of P. oligandrumis a multifaceted process which depends on the target species involved. P. oligandrumis nonpathogenic on 12 species of crops that belong to six families. It occurs on the root surface together with plant pathogenic fungi, predominantly in the regions of hypocotyl – taproot without penetrating the plant tissues. The plant growth is reportedly stimulated by this species. P. oligandrum can be utilized for biological control on a wide spectrum of crop plants. Different methods of application have been developed. The most effective activity of this microorganism is the mycelial growth inhibition of the plant pathogenic fungi.

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Trichoderma form-species are among of the important antagonists of plant pathogenic fungi and also induce resistance in field crops. Therefore their isolation and identification could be helpful for applying them in biological control. They isolate by pour soil diluted suspension on Dawet, Peptone – Rose Bengal, or modified Potato- Dextrose-Agar mediums. Species can identify based on colony characteristics, growth characteristics and morphological characteristics of conidiophores, phialids, and conidia. Eighty-five isolates of Trichoderma from 25 soil samples, from 8 regions of the Fars province sugar beet fields, isolated and purified with this method. With studied their characteristics eight form-species of Trichoderma identified with names: T. asperellum, T. atroviride, T. brevicompactum, T. harzianum, T. longibrachiatum, T. spirale, T. tomentosum and T. virens . Methods of isolation, identification and morphological characteristics of these fungi described.

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Regarding to the need of improving the quality and quantity of agricultural products, the science of plant protection has been taken under consideration. Accurate identification and detection of plant pathogens is one of the best ways for successful plant disease management. One of the useful methods is analysis of the volatile organic compounds, which spread from diseased plants. In this method, specificity of the volatile organic compounds and also the factors that affect the identifying of plant diseases and effective methods on these compounds are important. First, these compounds should be collected and then be analyzed. The best method for analysis of these compounds is dynamic sampling followed by gas chromatography and using the proper probes. Although the high costs of the tools make it difficult to apply this method for agricultural purposes, but by using the statistical methods and estimations the costs can be decrease.

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DNA microarrays technology is a method for studying the gene expression in large scale, based on investigations of probes and targets hybridization. This technology can also be used for identification of different organisms. DNA microarrays are a set of probes linked to a solid phase as microscopic spots. After hybridization of targets to probes, hybridization level is calculated by means of different methods such as measuring refulgence of fluorescent dyes to determine gene expression level. A microarray examination has different steps: making DNA chips, preparing targets, performing hybridization, and gathering and analyzing data. DNA microarrays technology can be used in different fields of plant pathology such as identification of different species of fungi, bacteria, nematodes and viruses, and to study plant-pathogen interaction.

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Development of human civilization is closely associated with agricultural crops. The major threat to crops posed by fungal diseases results in the use by growers of enormous amounts of chemicals. Fungicides are compounds, which are toxic to fungi. These materials have been applied for a long time to reduce losses and increase the quality and yield of the agricultural products. Today in addition to improving the quality and quantity of agricultural products and protecting plants by fungicides, the fungicide resistance problem must also be considered. The appearance of resistance has an important factor in limiting the efficacy and useful lifetime of fungicides. In general, systemic fungicides have been associated with resistance problems to a much greater extent than have non-systemic (protectant) fungicides. However, there are some exceptions. This paper discusses the resistance mechanisms to fungicides of some phytopathogenic fungi (e.g. altered target site, reduced uptake of fungicide, removal, detoxification or metabolism of fungicide) at the molecular level and describes methods used in the molecular detection of fungal resistance (e.g. RFLP-PCR, and allele specific real-time PCR) to fungicides.

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Phytoplasmas are some plant pathogens that establish and propagate in plant phloems. They have transmitted by sucking insects. Phytoplasmas have a different lifecycle as compare to bacterial pathogens. They have ability to infect different hosts two different kingdoms, planta and animalia (insects). They systemically infect their hosts. Phytoplasmas have various approaches for adaptation to their hosts. Some of adaptation mechanisms include: changes in the level of gene expression, variation and recombination in extrachromosomal DNA and potential mobile units, production of effectors and suppression of defense signaling pathways. These approaches enable them to establish, propagate and infect various hosts. Recognizing these strategies would be a major step on the effective management of these pathogens.

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Shenavar  O. & Mostowfizadeh-Ghalamfarsa  R. 2015. Computerized interactive keys for identification of fungi. Plant Pathology Science 4(2):41-52

Accurate identification of fungi and fungus-like organisms is one of the most important steps for finding an approach to employ or control them. Nevertheless, this process is usually laborious and slow. Application of interactive keys is one of the ways to save the time and have an accurate identification of the species. An interactive key is a computer program in which the user enters morphological or molecular attributes of the specimen and the program compares them with the data of its database to find a match species with the highest similarity.  Such keys also allocate separate images and other data for any known species. In this paper some of the interactive identification keys and their function is discussed.

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Safaiefarahani B. & Mostowfizadeh-Ghalamfarsa  R. 2017. Phytophthora spp. interspecific hybrids and their danger for agriculture. Plant Pathology Science 6(1): 33-46.

Interspecific hybridization is an important evolutionary process contributing to adaptation and speciation. During the last decade, advances in the molecular taxonomy techniques have led to increasing the number of descriptors interspecific hybrids in the genus Phytophthora. In Phytophthora hybrids, inheriting and recombining genes from both parents may result in increased aggressiveness and broader host range compared with either parent. Some Phytophthora natural hybrids have also been reported in Iran to date. Consequently, identification, pathogenicity and host range tests of these hybrids as well as preventing the formation of new hybrids before experiencing large economic losses are recommended for management of plant diseases caused by this fungal-like organisms.

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Mirtalebi M. & Mostowfizade-Ghalamfarsa R. Integrated management of gray mold disease. Plant Pathology Science 6(2):43-54.
 
Gray mold caused by Botrytis cinerea, is one of the most important postharvest diseases on fresh fruits and vegetables worldwide. The disease may start in the field and remain as a latent infection and then develop after harvest, during transportation, packaging, storage and marketing. Nowadays, application of fungicides is the main strategy to control the gray mold disease in conventional agriculture. The presence of fungicide residues in edible fruits and vegetables is a concern for consumers because pesticides are known to have potential harmful effects. Therefore, the search on finding the safe and effective disease control strategies has been accelerated. Integrated management of the disease by using some methods like optimal method of irrigation and fertilization, biological control, use of bioagents, disinfection of fresh fruits and vegetables after harvesting, storing and shipping in a cool and dry condition with low humidity and suitable ventilation are suggested.

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DOI: 10.2982/PPS.8.1.24.

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Fekrikohan S and MostowfizadehGhalamfarsa R (2019) Integrated management of diseases caused by graminicolous fungi. Plant Pathology Science 8(2):58-69.
DOI: 10.2982/PPS.8.2.58