نشریه دانش بیماری شناسی گیاهی
سال دهم شماره 1 (پیاپی 19، پاییز و زمستان 1399)

Powdery mildew caused by Podosphaera pannosa is one of the most important diseases of peaches and nectarines worldwide, including Iran. The aim of this research was to investigate the response of peaches and nectarines under cultivation in Iran to the disease.

Reaction of ten peach cultivars vs. Robin, Early Red, Red Top, Shasta, Amesdn, Velvet, Anjiri, Paeizeh, Dixi Red, and Sun Crest, and ten nectarine cultivars vs. Independence, Stargold, Sangold, Sanking, Giuta, Shabrang Karaj, Vega, Orion, Jiova and Veinberger were evaluated for disease in natural and artificial infection conditions in two experiments in a randomized complete block design with three replications over two years at the Meshgin Shahr Agricultural and Natural Resources Research Station.

Analysis of variance of experimental data showed that there was a significant difference between cultivars of each plant at a probability level of 1%. Peach cultivars Anjiri and Red top were very resistant, Velvet, Shasta and Early red ‎were resistant; Amesdn, Dixi red and Robin were moderately resistant; Sun ‎crest was susceptible and Paeizeh was in very susceptible. Weinberger nectarine cultivars were resistant and Independence, Stargold, Sanking, Giuta, Shabrang Karaj, Vega, Orion and Jiova cultivars were semi-resistant and Sangold was very susceptible to disease.  

Eighty percent of the studied peach cultivars are very resistant to semi-resistant and 20% sensitive and very sensitive, 90% of the studied nectarine cultivars are resistant to semi-resistant and 10% susceptible to powdery mildew. Findings of this research should be considered in the management of peach and nectarine powdery mildew.

Antibacterial, antifungal and antioxidant activity of methanolic extracts of Colocynth (Citrullus colocynthis) seeds, Camelthorn  (Alhagi maurorum) fruit and Chinaberry (Melia azedarach) leaves on eight bacteria and three fungi, which usually cause damage to agricultural products examined in this research.

Antimicrobial activity of selected plants in six concentrations on 11 microorganisms including, three gram-positive bacteria vs. Bacillus subtilis, Staphylococcus aureus, and Rathayibacter toxicus, and five gram-negative bacteria vs. Escherichia coli, Pseudomonas aeruginosa, Pseudomonas syringae subsp. syringae, Pseudomonas viridiflava, and Xanthomonas campestris pv. campestris, as well as three fungi vs. Pyricularia oryzae, Fusarium oxysporum and Botrytis cinerea was measured using the disk diffusion method. Also, the antioxidant activity of the extracts of these  plants was evaluated by measuring the enzymes of catalase and guaiacol peroxidase and evaluating the ability to trap DPPH radicals. In addition, the amount of total phenols and flavonoids in these plants extracts were measured.

Methanolic extract of Colocynth seeds had the highest antibacterial activity, the highest activity of catalase and guaiacol peroxidase enzymes and the highest percentage of DPPH radical inhibition. Methanolic extracts of these plants had no effect on fungal colony growth.

Methanolic extract of Colocynth seeds can be considered as potential sources of bactericides in agriculture.

Root-knot nematodes are one of the most important groups of plant parasitic nematodes in terms of economic damage to agricultural products. Biological control is one of the most environmentally friendly methods for management of nematodes.

The effects of aqueous extracts of jimsonweed (Datura stramonium), metel (Datura metel) and henbane (Hyoscyamus niger) was evaluated against Meloidogyne javanica on cucumber, under greenhouse condition, in this study. Cucumber plants were inoculated with suspension of eggs and second stage juveniles of nematode. After a week, 1.66% concentration of each plant extract were irrigated in the pots. Plants were harvested after 45 days and some plant growth parameters and nematode reproductive parameters were recorded.

The extract of any of the plants did not affect the number of knots on the roots and per gram of the roots. However, number of egg- masses per root and gram of root, treatments including nematodes and extracts had fewer masses compared to treatments without plant extracts. Final population and reproductive factor had also lower values in treatments with plant extract compared to treatments without it. In addition, the plant extracts had no negative effect on the growth factors of the cucumber in the greenhouse.

The extracts of Datura stramonium, Datura metel and Hyoscyamus niger reduced the reproduction of nematodes respectively, therefore they can be considered as potential agents in biological control of root-knot nematodes.

Poaceous plants such as corn, wheat, barley, sorghum, oats and millet are an important part of agricultural ecosystems. Smuts are one of the most important fungal diseases of these plants, which often cause economic damage and the destruction of part or all of their yields.

Poaceous smut infected plants in farms and pastures of Markazi and Lorestan provinces were sampled. Morphological characteristics of these fungi and their germination type of teliospores were studied with bright field and fluorescent microscopes and identified using valid keys. The phylogenetic relationship of these fungi with other smuts was also investigated based on ITS-rDNA region sequencing.

According to the type of host, morphological characteristics and mode of teliospores germination 12 species vs. U. maydis, U. hordei, U. turcomanica, U. avenae, U.nuda, U. bromivora, U. cynodontis, U. tritici, Tilletia laevis, Tilletia controversa Sporisorium reilianum and S. cruentum were diagnosed. The morphological characteristics and phylogenetic relationship of these fungi with other smuts are described.

The smuts of poaceous plants in Markazi and Lorestan provinces include eight species of the genus Ustilago, two species of the genus Sporisorium and two species of the genus Tilletia.

Canola is one of the most important oilseeds in the world. Fusarium species can causes of canola root and crown rot.

In order to identify Fusarium species associated with rapeseed, some samples of the roots and crown of infected and suspicious plants were taken from rapeseed fields in the counties of Lorestan Province during the 2018 growing season. The samples were transferred to the laboratory and pathogenic fungi isolated and purified using specific and public media and then identified with valid keys.

A total of 88 isolates were obtained from the collected samples, which due to the morphological characteristics as F. acuminatum, F. culmorum, F. diversisporum, F. oxysporum, F. sambucinum, and F. solani. F. culmorum with 21 isolates (23.86%) and F. solani with 7 isolates (7.95%) had the highest and lowest frequency percentage, respectively.

Canola is reported for the first time as a new host for F. diversisporum and F. sambucinum in Iran.

Changes in the resistance to bacterial soft rot in potatoes can be linked to the expression of pathogenesis-related (PR) genes. The aim of this study was to investigate the relationship between the accumulation of PR genes and the induction of resistance through infection of potato tuber cells with pathogenic bacteria at different temperatures in order to effectively combat bacterial soft rot disease in potatoes.

Pectobacterium carotovorum 2A, Pectobacterium atrosepticum 36A, and Dickeya dadantii ENA49 were used in this study. For bacterial infection, the potato cultivars semi-resistant cultivar Scarab  and susceptible cultivar Vesnianka, were used. The factorial experiment with three replications was carried out according to a completely randomized design. The relative level of mRNA copies of PR genes was determined by RT-PCR using primers of these genes. The mean values were compared according to the LSD test.

The experiments demonstrated the induction of PR-3, PR-5t and PR-10 in potato tuber cells in response to infection with  P. carotovorum 2A, P. atrosepticum 36A  and D. dadantii ENA49. It has been shown that the degree of induction of resistance genes depends on the temperature and the potato cultivar.

It can be concluded that significant changes in potato resistance to bacterial soft rot at temperatures of 28 and 33 ° C are associated with the expression of these PR genes.

Tomato is one of the most important and most widely consumed vegetable in the world. Tomato also is one of the most important products in West Azerbaijan Province of Iran, which plays an important role in the province's agricultural economy. Accurate bacterial disease diagnosis is the first and most important step in designation methods of disease management.

Tomato farms in the suburbs of the province cities were visited and diseased plants were sampled. Bacteria were isolated and purified from patient tissues and identified based on phenotypic and molecular characteristics. The bacterial pathogenicity test was performed according to Koch principles.

Tomato bacterial pathogens in this province include Clavibacter michiganensis subsp. michiganensis, Xanthomonas vesicatoria, Pseudomonas syringae pv. tomato, P. syringae pv. syringae and Dickya chrysanthemi, agents of bacterial canker,  bacterial spot, bacterial speck,  syringe leaf spot and soft stem rot. Disease symptoms, phenotypic and molecular properties of pathogenic bacteria, previous reports on these bacteria from Iran and their distribution in different regions of West Azerbaijan Province are presented.

These bacteria, with the exception of the tomato bacterial canker agent, are reported for the first time from West Azerbaijan province.

Fusarium root and crown rot is one of the most important wheat diseases in the world, which causes a significant reduction in yield. The disease is also common in many wheat production areas in Iran. F. acuminatum, F. avenaceum, F. culmorum, F. solani, F. semitectum, F. equiseti, F. crookwellense, F. lateritium, F. moniliforme, F. oxysporum, F. pseudograminearum, F. sambucinum, F. subglutinans,F. proliferatum, F. longipes, F. nygamai, F. compactum, F. diversisporum, F. fujikuroi, F. javanicum, F. flocciferum and F. tricinctum have been reported from rotten tissues of wheat root and crown in Iran and F. culmorum and F. pseudograminearum are known as the most important disease agents. Disease management methods including crop rotation, removal of diseased plant debris, setting planting date, biological control, seed disinfection with protective fungicides and cultivation of relatively resistant cultivars are described in this article.

Walnut is one of the most important fruit trees in Iran, which is always exposed to pathogens, especially bacteria. The three most important bacterial diseases of walnut in Iran are bacterial blight (Xanthomonas arboricola pv. juglandis), skin cankers (Brenneria nigrifluens, Brenneria rubrifacians) and crown gall (Agrobacterium tumefaciens). Bacteriological characteristics and pathogenicity of pathogenic bacteria, methods of managing these diseases, along with suggestions for identifying resistant genotypes of walnut trees by molecular methods are described in this article.

Many plant pathogens can spread into irrigation water in farms, gardens or greenhouses and cause disease in various crops. So far, a large number of plant pathogens including 43 fungal-like organisms, 27 fungi, eight bacteria, 26 viruses and 13 nematodes have been isolated and reported from water sources and water transmission systems. In many greenhouses, various pesticides are used to prevent the spread and control of these pathogens, which imposes costs, soil or water pollution, and the possibility of resistance in pathogens. Different methods of water treatment to control aquatic pathogens in the irrigation system using chemicals such as chlorine, chlorine dioxide, copper, silver and ozone, physical methods such as water filtration, heat, ultraviolet rays and the use of biosurfactants such as rhamnolipid and  nitrapyrin, are described in this article.

Today the ecological, ecological and sociological problems of conventional agriculture are of great concern. Accordingly, organic farming should be viewed as an alternative approach that provides safe and healthy nutrition by eliminating synthetic pesticides and fertilizers with the least loss of nutrients and energy and the least negative impact on the environment. Organic farming is guided by the idea that all processes within an agro-ecosystem are interdependent and it aims to achieve efficiency, diversity, self-sufficiency, self-regulation and resilience through natural processes using the ecological possibilities of the agricultural system. Disease management in organic farming is based on maintaining biodiversity and soil health. In this review, a brief description of organic farming is given first. The next other practices used in organic farming to control disease include sanitation, organic soil improvement, long-term crop rotations, reduced tillage, the right harvesting time, the selection of crops and varieties, and the use of catch crops and also, catch crop cultivation. In conclusion, organic farming has the potential to improve the recycling of biomass and optimize the availability of nutrients and ensure favorable soil conditions for plant growth.

Plant viruses cause major losses to agricultural crops worldwide. Plants react to the virus infections via several defense mechanisms, such as ubiquitination. Ubiquitin (Ub) and ubiquitin proteasome system (UPS) play key role in the function modification and degradation of proteins in plants. Ub attachment to the cellular proteins alters the stability, the cellular establishment or activity of the target protein. The key role of UPS has been revealed in defense mechanisms and other plant processes. Viruses as obligate intracellular parasites have evolved mechanisms to interfere UPS. In some cases, it has been shown that viral proteins were targeted by this system. Ubiquitination plays an important role in plant–virus interaction which can lead to plant resistance or pathogenicity in the host plant. Therefore, further understanding of UPS and its role in plant-virus interaction can develop novel methods to increase resistance to viral infections in plants.