نشریه دانش بیماری شناسی گیاهی
سال هشتم شماره 2 (پیاپی 16، بهار و تابستان 1398)

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.

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.

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.

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.

Cereal cyst nematodes (CCN), Heterodera species, are important parasitic nematodes of cereal. Potato cyst nematodes (PCN), Globodera species, are also serious pests of potato world-wide. Continuous monitoring of these nematodes is necessary to prevent their damage to their host plants. This study was conducted to determine the distribution and density of these nematodes in Ardabil province, northwest of Iran, where potatoes are planted in rotation with cereals.

One hundred and two soil samples were collected from potato fields in the suburbs of Ardebil, Nair and Namin cities in the first year, and 116 soil samples were collected from the wheat fields that were cultivated in the rotation with potato in the second year. The samples were transferred to the laboratory and examined for cyst nematodes. After isolating the cysts, identification of the species was performed based on morphological and morphometrical characteristics of the cysts and the second stage larvae.

Examination of the collected samples in both of two years indicated the presence of CCN in some soil samples, but PCN were not observed in none of the soil samples. The morphological and morphometrical data of isolated cereal cysts and comparison with valid identification keys led to the identification of Heterodera filipjevi. Mean numbers of the cysts with eggs and larvae in those samples that were collected in the first and second year were respectively 0.76 and 0.11 in 100 g of the soil. Wheat fields of Ardebil had the highest and fields of Nair had the least number of cyst nematode.  

The results of this study showed that some of the wheat fields in the province were infected with H. filipjevi and potato fields were not infected with any cyst nematode.

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.

During recent years, the newly emerging disease, citrus sudden decline (CSD) has destroyed many of citrus trees grafted onto bael rootstock in the south of Kerman Province. The disease is caused by Candidatus Liberibacter asiaticus and its simultaneous infection to soil born pathogens or Ca. Phytoplasma aurantifolia, or heat and drought stresses can increase the disease severity and appearance of the decline symptoms. Using the healthy and certified rootstock, using the Sour Orange or Volkamer Lemon as rootstock, control of the sucking insects at the time of flushing, optimum irrigation with appropriate distribution especially during the summer season, control of soil born fungi and nematodes, avoiding stress to plant and appropriate pruning are recommended for prevention and management of CSD disease in the south of Kerman Province.

Bacterial canker disease is one of the most destructive diseases of walnut trees that causes die back and plant decline and also great damages to quality and quantity of fruits. The disease can be observed in two forms, at depth and the surface of the bark which cause by two bacteria, Brenneria nigrifluens and B. rubrifaciens, respectively. The most important way of the pathogen penetration is the wounds in the trunk and branches which are occurred due to human ‎activities or mechanical harvesting equipment. The disease becomes severe with the deep irrigation and when the nutrition is insufficient and ‎temperature and humidity are high.‎ Current paper explains history, importance, symptoms, biology, host range, sampling and isolation method also differential characteristics of bacteria and methods of disease management.

Blight disease caused by Mycosphaerella rabiei is the major constraint for chickpea production worldwide. Pathogenicity of pathogen and the analysis of its genetic diversity in pathogen population are necessary for management of the disease. Different strategies such as seed treatment, application of resistant cultivars, adjustment sowing date and integration of resistant genotype with post-infection application of fungicides have been recommended to reduce the losses caused by the disease. The use of resistant cultivars is the best management strategy to minimize yield losses due to blight. But because of the considerable variation in pathogenicity of the fungal population and partial resistance in germplasm of chickpea the effectiveness of resistant cultivars is limited. Different aspects of the biology, pathogenic and genetic diversity, resistance inheritance and the management options are discussed in this paper.

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.

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.

DNA sequencing is used by virtually all branches of biological research. Among the first advanced sequencing technologies, scientists were able to elucidate genetic information from any particular biological system using the Sanger sequencing method. Although Sanger sequencing generates high quality sequencing data, its limitations such as scalability, speed and resolution often preclude scientists from obtaining the essential information. To overcome these barriers, next generation sequencing technique (NGS) was introduced at the beginning of the 21st century. This technique provided a highly efficient, rapid, and low cost DNA sequencing platform beyond the reach of the standard and traditional DNA sequencing technologies that developed in late 1970s. In 2009, NGS technologies began to be applied to several areas of plant virology including virus/viroid genome sequencing, discovery and detection, ecology, epidemiology and replication. It is expected that NGS plays very significant roles in many plant virology researches.

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.

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.

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.

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.

Nano-chitosan can be used as a bio-fungicide to replace chlorothalonil as a chemical fungicide for disease management.

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.

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.

Eighteen fungi from eight genera vs. Aspergillus, Penicillium, Alternaria, Ulocladium, Stemphylium, Paecilomyces, Rhizopus and Fusarium were identified in this study.

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.