Plant Pathology Science

Wheat is one of the most important cereals grown as human and animal food in the world, including Iran. This crop is infected by various pathogens such as fungi. Graminicolous fungi are important pathogens which cause root and crown rot, leaf blight and black spot on wheat. Some methods, with high efficiency and safety for human and environment, have been employed for controlling these diseases. Since the activity of these fungi depends on some factors such as soil temperature, pH, moisture and nutrients, the proper agricultural practices before planting and suitable irrigation and good fertilization would be effective in pathogen control. Various species of Trichoderma, arbuscular endomycorrhizal fungi and some bacterial species may control the disease through some mechanisms such as biofilm production, plant growth promotion and enzyme production. Generally, integrated management with the aid of simultaneous application of several control measures would give the best results.

Geminiviruses (Geminiviridae family) with small circular ssDNA genome are encoding just four to seven proteins on virion and complementary-sense strands of their genomes. To have a progressive infection, they are dependent mostly on host cellular machineries and interact with wide range of different host plants factors and processes. Geminiviruses alter the cell cycle in infected plants and they can support replication of viral DNA. They change host gene expression patterns, inhibit cell death pathways, alter macromolecule trafficking and interfere with protein modification to redirect or suppress host defenses and hormones signaling. Geminiviruses encode gene silencing suppressors to interfere with post-transcriptional gene silencing and alter plant DNA methylation and microRNA (miRNA) pathways, often causing developmental abnormalities. Here, the geminiviruses are discussed as one of the most destructive plant viruses and their proteins interactions with host cell factors and pathways are described.

Ash tree is an important symbol of the urban green space in the world, which is also used in the construction of home and sport equipment. Ash dieback disease caused by Hymenoscyphus fraxineus is widespread in the most forests and green areas of the European countries. The disease was first observed in Poland and Lithuania in the early 1990s. The geographical spread of the pathogen has increased in the last two decades and so it is now is considered as a serious threat to the Ash trees. Initial infection is caused by ascospores released from apothecia formed on the previous year's leaves dropped. Disease management can be achieved by prevention and quarantine methods, sanitation, identification and cultivation of resistant cultivars and the use of chemical fungicides. The disease has not been reported from Iran so far, however, the possibility of entering the disease in the future is unclear. Therefore in this article we discuss the various aspects related to this disease including symptoms, pathologic biology, and management methods.

Iranian Pistachio is one of the most important horticultural product in export market. Crown and root rot caused by Phytophthora species is the most serious disease of plant, which annually destroys a considerable number of mature and young trees. This disease has been reported from all provinces of Iran. The pathogen is soil-borne and is distributed by sporangia or the released zoospores and infects the healthy trees. In the most Pistachio orchards, the key factors of disease development are the sensitivity of pistachio crown to Phytophthora and the flooding method of irrigation. The symptoms of the disease are include blight in early spring, drying of the green leaves during the growing season, gum exudation from the crown of tree  and the root rot. Gummosis can be successfully controlled by integrated disease management including orchard constructing in non-infected areas, using resistant or tolerant cultivars, using healthy rootstocks, improving the irrigation methods and avoiding the direct contact of water with tree crown, isolating the contaminated parts of the orchard from the healthy parts, using suitable fungicide, and biological control based on Trichoderma and Bacillus species.

 Introduction: Black cumin, an annual flowering plant in the family Ranunculaceae, is a medicinal herb with many pharmacological properties. Crown and root rot disease of this plant has been reported in most countries worldwide. This study was conducted to investigate the occurrence of this disease and identifying the causal agent in southwest of Iran. Materials and Methods: Black cumin farms were visited in Kohgiluyeh and Boyer-Ahmad province and southwest of Iran. Plants with crown and root rot were sampled. Pieces of infected root and crown were washed with tap water, dry blotted and plated on CMA-PARP. In total, 17 isolates of two different fungus-like species were isolated from rotted root and crown. Species identification was done based on morphological characteristics and temperature requirement. Pathogenicity test of the isolates were done on 3-week-old seedlings of Baft cultivar under greenhouse condition. Results: Eleven isolates were identified as Pythium aphanidermatum and six isolates as Phytophthora drechsleri. Both of these fungus-like species were pathogenic on the tested black cumin variety. Conclusion: Crown and root rot disease is present in the farms of black cumin in the southwest of Iran. The causal agents of this disease were identified as Pythium aphanidermatum and Phytophthora drechsleri. The black cumin cultivar Baft is susceptible to these pathogens.

Introduction: The Fungi which are able to grow at the temperatures above 40 degrees Celsius are known as thermophilic fungi. So far, no study has been carried out on fungi in desert areas of Iran so the present study was aimed to isolate and identify the fungi in desert areas of Yazd province. Materials and Methods: Four desert regions of Yazd province were visited and samples were taken from soil and plant roots. The fungi were isolated by soil dilution method and were cultured on potato-agar extract medium. Genus and species of fungi were identified by valid identification keys. Results: Eighteen fungi from eight genera vs. Aspergillus, Penicillium, Alternaria, Ulocladium, Stemphylium, Paecilomyces, Rhizopus and Fusarium were identified in this study. Conclusion: The species of Penicillium and Aspergillus were the most abundant species in desert soils of this province. All fungi identified in this study are reported for the first time from Iranian desert soils.

Introduction: Early blight caused by Alternaria species is one of the most important tomato diseases in the world. The disease has been reported from most areas in Iran with up to 90% infection. This study was conducted to investigate the effect of nano-chitosan on the severity of the ‎disease and its use as a replacement‎ of the chemical fungicide, chlorothalonil. Materials and Methods: Diseased tomato plants of fields and greenhouses of Fars province in southern Iran were sampled. Pathogens were isolated from diseased tissues, purified and identified by studying their morphological characteristics. The effect of nano-chitosan at three concentrations of three, five and seven grams per liter and the fungicide chlorothalonil were tested before and after inoculation of two pathogens. The disease severity indexes were measures in Sunseed and 16 cultivars of tomato under greenhouse conditions using a factorial experimental in completely randomized design with four replications. The data were analyzed with comparing the means. Results: The isolated pathogens were identified as A. solani and A. alternata. Results of the greenhouse experiment showed that A. solani was more aggressive than A. alternata and the cultivar 16 was more resistant to the disease. Nano-chitosan at 5 and 7 mg/ l significantly reduced disease severity indexes when use before pathogen inoculation, and at 7 mg/l when use after pathogen inoculation. Conclusion: Nano-chitosan can be used as a bio-fungicide to replace chlorothalonil as a chemical fungicide for disease management.

Introduction: Citrus bacterial canker caused by Xanthomonas citri subsp. citri is an economically important disease in many tropical and subtropical countries. Several pathotypes of this pathogen have been described which, in addition to certain genotypic features, are distinguished above all by their geographical origin and their host range. Citrus bacterial canker disease is wide spread in Iran and a major threat to the production of Mexican lime (Citrus aurantifolia). Therefore, management of citrus canker is inevitable in citrus growing areas where citrus canker has been established. Application of copper-based bactericides is a standard control measure for management of citrus canker worldwide. Therefore, their long-term use leads to the development of resistant isolates. Plant extracts and essential oils with an antimicrobial effect have become particularly important as an environmentally friendly method for the treatment of plant diseases. Many researchers have recently focused on studying plant extracts and essential oils that contain antimicrobial compounds. Material and Methods: The present study was carried out on the antibacterial effect of ‌Common yarrow (Achillea millefolium), Ginger (Zingiber offcinale), Golden marguerite (Anthemis tinctoria), Fennel (Foeniculum vulgare), Common sage (Salvia officinalis), Gum tragacanth (Astaragalus gossypinus), Summer savory (Satureja hortensis) and True cardamom (Elettaria cardamomum) against two pathotype of Xanthomonas citri subsp. citri under laboratory and greenhouse conditions. Results: All essential oils have an inhibitory effect on multiplication of Xanthomonas citri subsp. citri. The antibacterial test results showed that the essential oils of Ginger and True cardamom strongly inhibited the growth of Xanthomonas citri subsp. citri pathotype, especially the pathotype A*, whereas other essential oils showed moderate to weak activities. Conclusion: The essential oils of these eight plants, especially ginger and cardamom, have good potential for the management of citrus bacterial canker.

Introduction: Ganoderma lucidum, medicinal mushroom, is one of the most effective traditional medicine in East Asia. The mycelium, the spore and the basidiocarp contain about 400 different bioactive compounds with polysaccharides, peptidoglycans and triterpenes as active ingredient groups of medical value. Underwater cultivation is one of the most reliable technologies to produce the industrial biomass of this mushroom, which contains anti-tumor and anti-cancer polysaccharides. Regarding the growth of fungal mycelium, it is related to various environmental factors such as pH, temperature and available nutrients. The aim of this study was to determine the influence of pH, temperature and different concentrations of the carbon and nitrogen sources on the growth rate of fungal biomass in sugar cane molasses. Materials and Methods: The first part of the study dealt with the morpHological and molecular identification of an Iranian isolate from G. lucidum.  Then the effects of carbon sources of arabinose, maltose, cellulose and xylose at concentrations of 0.1, 0.2 and 0.3%, and nitrogen sources of yeast extract, MgSo₄.7H2O, peptone and K₂Hpo₄ at concentrations of 0.2, 0.3 and 0.4%, pH 4, 4.5, 5 and 5.5, and a temperature of 25° C, 28° C, 32 ° C and the number of 2, 3, and 4 inoculum particles of 5 mm² for the production of mycelium biomass of G. lucidum, in sugarcane molasses was studied, in completely randomized design experiments with four replicates for each treatment in vitro. Results: A comparison of the mean dry weight mycelium of G. lucidum produced with different treatments showed the significant differences between the treatments with a probability of 5%. The highest yield of G. lucidum was obtained in peptone with concentration of 0.3%, maltose with concentration of 0.2%, pH=5, 3 inoculum particles with 5mm² diameter, at 28°C. Conclusion: Sugar cane molasses can be used as a cheap and inexpensive medium for the biomass production of G. lucidum. For the first time this study showed that by adding peptone with concentration of 0.3%, maltose with concentration of 0.2%, to sugarcane molasses, with 3 particles of inoculum with 5mm² diameter, in pH=5, and 28°C, the highest biomass of this medicinal mushroom could be produced.

Introduction: Gray mold caused by Botrytis cinerea is the most important disease after strawberry fruit harvest. The use of chemical fungicides can have a negative effect on the health of consumers, so the use of plant essential oils for disease management has been considered. The effect of six plant essential oils on the pathogen and the contamination of strawberry fruits was investigated in this research to identify suitable essential oil to control the disease. Materials and Methods: The pathogen was isolated from infected strawberry fruits in northeastern Iran. The inhibitory effect of different concentrations of peppermint, savory, caraway, cumin, eucalyptus and thyme essential oils on mycelial growth and germination of the pathogen spores was tested by mixing them with culture medium. Then, the effect of these essential oils in liquid and vapor phases on the contamination of strawberry fruits was tested. After normalization, the data of these experiments were analyzed by analysis of variance with MSTAT-C software and the means were compared with Duncan test. Results: Essential oils of caraway and eucalyptus had the greatest effect in inhibiting the growth of pathogen mycelium. Essential oils of caraway, cumin, savory, thyme and peppermint had the greatest effect in inhibiting the germination of pathogen spores. The essential oils of caraway, cumin, savory, thyme and peppermint in the vapor phase, the essential oils of caraway and eucalyptus in the liquid phase, prevented further contamination of the fruit. Conclusion: The findings of this study show that all of these plant essential oils can significantly prevent the growth of mycelium and germination of pathogen spores and contamination of strawberry fruits, but the effect of caraway essential oil in most cases is better than others. Thus, it can be used as an alternative to fungicides on strawberry fruit.

Betasatellites, as begomovirus-dependent small circular single-stranded DNAs, are multifunctional agents that trigger disease symptoms, suppress gene silencing pathways and also interact with various cellular pathways and factors. These subviral elements have a conserved genome organization that encodes only a functional open reading frame on the complementary sense strand βC1. The encoded beta satellite protein affects only the helper begomovirus cycle factor. The small size with a strong promoter sequence and the ability to replace βC1 with foreign genes made beta satellites suspected tools for the investigation of functional genes. As we expand our knowledge of begomovirus / beta satellite complexes and their interactions with host plants, we develop management approaches for the expansion of begomoviral destructive diseases.

Plant diseases play a critical and limiting role in crop production and their control by using pesticides cause serious problems regarding food safety and environmental health and increase the need for other sustainable disease management techniques. Some of plant pathogens may infect the aerial parts of plants, but spent part of their life cycle in the soil and maintained their survival. In such cases, part of the life cycle of the plant pathogen in soil may be very important, even if that microorganism does not infect the roots. Mono culturing and cultivation of crops belonging to the same family increase the potential of disease incidence. Using and applying the suitable and correct cultural practices that limit damage of root diseases is necessary for sustainable management of soil-borne pathogens. Cultural operations, including the use of cover green crops, crop rotation, organic composts, certified seeds and propagative materials, amended organic material to soil, proper tillage systems, soil solarization, resistant cultivars, mycorrhizal fungi, all are reported and confirmed as management options for long time saving soil quality and good sustainable management of soil borne diseases.

Introduction: The Hoplolaimidae family is one of the largest and economically most important families of the order/ infraorder Tylenchida / Tylenchomorpha. The members of this family spread all over the world and can be found under different climatic conditions. Some species in this family are serious plant parasites and significantly reduce crop yields. Materials and Methods: In the forests of Khorramabad city in western Iran 70 samples were collected from the soil around the roots of hawthorn trees in the period of 2017-2019. After recording the properties of each sample, they were transferred to a laboratory and cooled at 4 °C. The nematodes were extracted from the soil using the tray method, then fixed and transferred to pure glycerin, and permanent slides were made. The morphological and morphometric properties of the nematodes were examined using a light microscope equipped with a Dino Capture camera. The nematode species were identified using scientific identification keys. Results: Five species of plant parasitic nematodes belonging to two genera of Hoplolaimidae were identified in this study, including Rotylenchus goodeyi, Helicotylenchus canadensis, H. digonicus, H. vulgaris and H. tunisiensis. Conclusion: R. goodeyi is reporting as a new record for the nematode fauna of Iran. Morphometrical and morphological characteristics of these nemadodes are described here.

Algae are the most important plant growth stimulants due to their high content of minerals, amino acids, vitamins and growth regulators such as auxin, cytokinin and gibberellin. Use of these stimuli in crops can improve rooting, yield, photosynthetic capacity and their resistance to pathogens. Application of algae (mainly seaweeds) against various plant diseases including bacterial, fungal, viral and nematode diseases as well as pests has been proven. Seaweeds are used as a powder or extract mixed with soil, or foliar spray to control of plant diseases. They are usually involved in controlling plant pathogens by inducing plant resistance, antagonistic activity by induced activity of other microorganisms, and enhancing plant growth. In general, seaweeds can be applied as biofertilizers, biostimulators and soil amendments in integrated plant diseases management programs.

 Introduction: Bunch feding is an important injurious disease of date palm. Materials and Methods: This research was carried out to its descsion making system in Abadan-Khoramshhar, Shadegan, Ahwaz, Mahshar and Behbehan regions of Khozestan province by climatic and geoststistical models from 2012 to 2016. Samples were taken randomly from 10 trees located in one date palm orchards of any villages Results:Results showed that the disease damage reached to the peak values in September. Forecasting model of damage factors have been significant at level 1 and 5 percent. Variography of distributions on different sites were calculated that the model nuggets for date palm bunch feding in Abadan - Khoramshhar, Shadegan, Ahwaz, Mahshar and Behbehan regions were 1.6, 1.7, 0.15, 0.51 and 2.5 kilometers respectively. These results show that errors of the damage estimation were low at the distances less than whithin sampling sapace. Effective ranges of variograms were 4.1. 12.9, 4.7, 1.9 and 11.06 respectively which indicated the date palm bunch feding distribution in region. Sill of models were 0.49, 0.76, 0.37, 0.31, and 0.51 respectively that at the distances more than these thresholds, correlations between the injury data were at the lowest level and could be monitored. Conclusion: The results of this study

Introduction: Chickpea blight, caused by Didymella rabiei, is the most limiting factor in chickpea production areas in the world, including the western provinces of Iran. The aim of this study was to investigate the pathogenic diversity of the isolates collected from western provinces of Iran (Ilam, Lorestan and Kermanshah) on differential lines of chickpea, as well as the relationship between pathogenic diversity of the isolates and their geographical origins. Materials and Methods: During the 2017-18 chickpea growing season, samples of infected plants were collected from fields in western provinces and transferred to the laboratory. Then 100 pure isolates of D. rabiei were obtained. Based on the location of collection, the isolates were divided into 20 groups. Based on the morphological characteristics, one isolate from each group was selected as a representative for greenhouse experiments. The pathogenic diversity of theses 20 isolates was assessed on eight differential lines of chickpea. The factorial experiments were performed in a completely randomized block design under greenhouse conditions. Results: The results of analysis of variance showed that there was a significant difference between differential lines and isolates at a probability level of p<0.01. Based on the response of the differential lines, the pathogenic isolates were grouped into three pathogenic groups, including pathogenic group 1 (weakly aggressive), group 2 (aggressive or moderately aggressive), and group 3 (highly aggressive). The isolates from Kermanshah and Lorestan Province were classified into Group 1 and the Ilam isolates into Groups 1, 2 and 3. The greatest severity of the disease was found in three isolates of Ilam province. The variety ILC3996 showed the highest resistance to all isolates. Conclusion: D. rabiei isolates from three western provinces of Iran are divided into three pathogenic groups: 1 (low aggressive), 2 (moderately aggressive), and 3 (highly aggressive). Highly aggressive isolates identified in Ilam province can be used in chickpea breeding programs to produce resistant cultivars to the disease.. The wild variety ILC3996 has resistant genes against these pathogenic groups and showed resistance to all of these isolates.

Introduction: Fusarium root rot with damage reported up to 85% of the crop yield, caused by Fusarium solani f. sp. phaseoli, is one of the most important bean diseases in the world. Biological control is a healthy and environmentally friendly way to manage this soil-borne disease. Materials and Methods: Bean farms in Kohgiluyeh and Boyer-Ahmad Province were visited and the rotten roots of diseased plants were sampled. Two isolates of the pathogen were isolated, purified and identified. The pathogenicity of these two isolates was tested on two bean varieties Drakhshan and Pak under greenhouse conditions. The colony growth inhibition rate of the hypervirulant isolate of the pathogen was assessed by 14 native isolates of Trichoderma harzianum, four isolates of Trichoderma virens, two isolates of Trichoderma atroviridae, and five native isolates of Pseudomonas florescens and P. florescens CHAO with hyperparasitic ability and production of antibiotics in vitro. Finally, the effect of four superior T. harzianum isolates, one T. atroviridae isolate and two P. florescens isolates on disease severity were examined in a completely randomized design in the greenhouse. Results: All isolates of three species of Trichoderma had the ability to hyperparasite and destroy pathogenic hyphae. Four T. harzianum isolates showed a more significant ability to produce non-volatile and volatile antibiotic materials. All treatments significantly reduced the disease severity, but a T. harzianum isolate was more effective in vivo. Conclusion: Fusarium root rot is also found in bean fields in southwestern Iran. Native isolates of T. harzianum, T. virens and T. atroviridae have the hyperparasitic ability on the pathogen. These fungi and isolates of P. florescens have the ability to inhibit the growth of the pathogen colony by producing antibiotic substances. Isolates of Trichoderma harzianum, T. atroviridae and P. florescens CHAO have the ability to reduce the severity of the disease in vivo.

By studying the structure of the nematode community, healthy and unhealthy soils can be identified in terms of biodiversity and nutrient network. This information is useful for managing soil nutrient networks. The study of the nematode population structure as a biological indicator of soil health is based on the assessment of biodiversity indices, nutrition groups, population dynamics, soil nutrient network profile, biomass and metabolic profile. Practical applications for studying the structure of nematode populations in agricultural and natural ecosystems are described.