Plant Pathology Science

Introduction: 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. Materials and Methods: 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. Results: 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.  Conclusions: 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.

 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.

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.

 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.

Rahimi F, Rahmanpour S, Rezaei S, Larijani K (2020). Identification of growth inhibitor of Sclerotinia sclerotiorum in Indian mustard leaf. Plant Pathology Science
9(2):28-36.       DOI: 10.2982/PPS.9.2.28.

Introduction: Sclerotinia sclerotiorum is the causal agent of white rot in aerial parts of a wide range of plants. The aim of this study was to compare the reaction of living tissue of Indian mustard leaves on the growth of this fungus under open and closed leaf stomata conditions. Materials and Methods: The pure isolate of the fungus was prepared by the hyphal-tip method on water-agar medium. An experiment was conducted in a fully randomized design with four treatments. The formation of fungal growth inhibiting compounds in the leaf tissue of all treatments was examined using GC-MS.
Results: Analysis of variance of the experimental data showed that the diameter of the fungal colony was significantly smaller in the treatment with open leaf stomata than in the other treatments. Gas chromatography data analysis showed that 1-propene-3-isothiocyanate as a volatile compound inhibits fungal growth in this treatment. Conclusion: The production of the volatile allyl isothiocyanate compound in Indian mustard leaf inhibits the growth of S. sclerotiorum.
 

Introduction: Lysine motif receptor-like kinases (LysM-RLKs) play an important role in the defense reaction of plants to diseases and environmental stresses. This study was conducted to investigate the effect of chitin as a stimulus for the expression of genes that encode LysM-RLKs. Materials and Methods: The expression levels of three genes PGSC0003DMP400010799, PGSC0003DMP400010800 and PGSC0003DMP400061331, which encoded LysM-RLKs due to chitin treatment (150 μg / ml) in young seven-week potato leaves of Jely cultivar, were examined in treated and control leaves. Results: Analysis of the gene expression data showed that the expression of all three genes increased significantly due to the use of chitin compared to the control. Conclusion: Increasing the expression of genes encoding LysM-RLKs using chitin can be effective to induce systemic resistance to plant diseases and environmental stresses.

Introduction: Root-knot nematode Meloidogyne javanica is the most economically important plant-parasitic nematode worldwide. Because of the environmental hazards of chemical nematicides used to control this nematode, there is an urgent need to replace these nematicides with alternative compounds that are environmentally friendly. Material and methods: An experiment was conducted to control M. javanica infestation on tomato plants (cv. Early-Urbana) using wood vinegar at the rates of 0.3, 0.6 and 0.9 percent (v/v), Effective Microorganisms (EM^®) at the rates of 5, 10 and 15 percent (v/v), humic acid at the rates of 0.2, 0.4 and 0.6 percent (v/v) and tervigo (positive control) at the rate of 0.4 percent (v/v), in greenhouse. Results: EM^® at the highest concentration (15%) was the most effective organic compound which reduced the nematode indices. Shoot length, shoot fresh weight and shoot dry weight increased by 41, 28 and 36%, respectively. The number of eggs, galls, egg masses per root system and reproduction factor were decreased by 58, 48, 49 and 57% in treated tomato with EM^® at the rate of 15%, compared to control (non-treated) plants, respectively. Conclusion: The organic compounds used in the present study are effective to control M. javanica on tomato under greenhouse conditions.

Introduction: 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. Materials and Methods: 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. Results: 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. Conclusion: 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.

Introduction: 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. Material and Methods: 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. Results: 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. Conclusion: Methanolic extract of Colocynth seeds can be considered as potential sources of bactericides in agriculture.

Introduction: 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. Material and Methods: 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. Results: 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. Conclusion: 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.