Nine Dictyuchus isolates were obtained from floating and decaying twigs and leaves in Anzali lagoon, Anzali County, Guilan province, Iran. They are interestingly distinguished from current Dictyuchus species by the presence of dictyoid and achlyoid type of zoospore discharge, abundant fusiform and spherical gemma, and the absence of any sexual apparatus. In addition, phylogenetic analyses of the internal transcribed spacer (ITS) region of the nuclear rDNA and cytochrome c oxidase subunit I (cox1) gene sequences using Maximum likelihood method indicate its novelty. We preferred not to introduce the isolates as new species due to low number of and sometimes unreliable sequences and lack of type species and suggested to verify Dictyuchus sterilis which has been excluded before. We discussed about taxonomy of the genus in details and provided a revised key to the species. In addition, it was shown that sterility in vitro might be common in this genus.

Pythium and Phytophthora are among the most well-known plant pathogens around the world that cause rotting of seeds, root, and crown, seedling death, and soft rot of fruits in contact with the soil. In this research, 347 isolates of these two genera and their close genus, Phytopythium were isolated from the cucurbits fields in Kermanshah province, Iran and examined in terms of morphological and physiolo-gical characteristics. ITS-rDNA region and the partial cytochrome oxidase II (cox II) gene from the selected isolates were amplified and sequenced to confirm the morphological identification. Based on the morpholo-gical, morphometrical, physiological, and phylogen-etic examinations, nine species of Pythium including P. aphanidermatum, P. dissotocum, P. catenulatum, P. kashmirense, P. middletonii, P. nodosum, P. oligandrum, P. torulosum, and P. ultimum; two species of Phytopythium including Pp. mercuriale and Pp. litorale, and three species of Phytophthora including Ph. melonis, Ph. nicotianae, and Ph. parasitica were detected. Among the species identified in this study, Pp. mercuriale was a new record for mycobiota of Iran and two species, P. aphanidermatum and P. ultimum were isolated more frequently.

Pythium irregulare oomycetes adapts with environmental changes including crude oil concentration by changing the composition of lipids in the cytoplasmic membrane and providing the required characteristics for adaptation in improper and stressful environmental situations. It was found that cultivation of Pythium irregulare LX oomycetes in the nutrient media with different concentrations of crude oil with 1.0, 2.0, 3.0, 5.0 and 10.0 (%), incubated for 5 days at 26-28oC on a rotary shaker (200 rpm) in aerobic conditions and deep culturing caused an increase in the lipid content and the unsaturation degree of fatty acids, confirming the correspondence between the increase of polar lipid/free sterol in the composition of membrane lipids’ ratio and that of polar lipids in general lipid fractions. Represented data shows that the process of adaptation of oomycetes to a stressful situation created with crude oil motivated the increase of the rate of membrane phospholipids with a high quantity of unsaturated fatty acids.

The formation of chlamydospores of Phytophthora parsiana, a newly described high temperature tolerant pathogen of woody plants, were investigated in culture media and in infected roots of susceptible host plants. Different solid agar media and cleared V-8 juice broth were inoculated with different isolates of P. parsiana and incubated for four days at room temperature before they were transferred to 4oC in the dark. Chlamydospore formation was monitored during twelve months. Infected almond and pistachio roots inoculated with the pathogen under greenhouse conditions were removed from soil, washed thoroughly and incubated within moist sterilized sand in plastic bags at 4oC for twelve months and examined monthly using light microscope. Chlamydospores were observed only on carrot agar two weeks after incubation and after four months in infected pistachio and almond roots. No chlamydospores were produced on other solid media and in CV8 juice during 12 months incubation. The average diameter of chlamydospore in culture and in roots were 29.7 and 32.47mmm with wall thickness 1.7 and 2.07 mm, respectively. Frozen culture medium and root containing chlamydospores at - 20oC for 72 hours resumed growth after thawing on Phytophthora selective medium. Sterilized non inoculated root segments colonized internally by the pathogen did not resume growth after freezing. The isolates did not produce oospores in single or dual cultures with P. capsici mating types. It is concluded that under natural conditions chlamydospore is a survival propagule of the pathogen.

Silver nanoparticles have antimicrobial activity and are used in various commercially produced products. In this study, the effects of two types of nanosilver formulations, including LS2000 and L2000 on two strains of Streptomyces and three phytopathogenic agents, Pythium aphanidermatum, Pythium ultimum and Fusarium solani were investigated. Streptomyces and phytopathogenic agents were cultured on ISP2 and PDA medium respectively supplemented with 0, 5, 10, 25, 50 and 70ppm of LS2000 and L2000. The influence of LS2000 and L2000 on mycelium of Streptomyces was investigated by atomic force microscopy (AFM). Colony forming unit (cfu) of the bacteria decreased in response to elevated concentrations of L2000. LS2000 completely inhibited growth of both strains at a concentration of 5ppm. The inhibitory effects of LS2000 on the phytopathogenic agents were more than L2000. P. aphanidermatum showed the highest tolerance to L2000 and only at 75ppm of the nanoparticles, the diameter of the colonies was decreased. High susceptibility of F. solani to L2000 caused a decrease in fungal colony diameter in lowest concentration of the nanoparticles. The growth of all phytopathogenic agents was decreased by LS2000 and completely stopped in a concentration of 50ppm. The results showed that LS2000 destroyed mycelial networks of the both bacteria in all tested concentrations. Vesicles appeared on the surface of the mycelium branches, subsequent to treatment with L2000. Based on the results, the inhibitory effects of silver nanoparticles on the beneficial soil bacteria were more than on the phytopathogenic agents. Therefore, more caution should be taken in using silver nanoparticles as a fungicide in agriculture.

The pathogen, Pythium aphanidermatum is one of the causal agents of sugar beet root rot in Iran. In order to evaluate the reaction of cultivars to the pathogen, at first, the screening method of evaluation was optimized. Then, a number of 24 cultivars that are commonly cultivated in Iran were evaluated against the pathogen. Three different evaluation methods in the greenhouse including grass leaf suspension, oospore suspension, and grass leaf suspension using through making wounds on the roots were compared with each other. A number of 12 cultivars were inoculated with these three inoculation methods. The results showed that positive and significant correlation of the three methods with each other. Then, 24 commercial sugar beet cultivars were evaluated with grass leaf suspension method under the greenhouse conditions. Based on the results of the evaluation of the 24 commercial cultivars of sugar beet and the comparison of the disease index of Pythium root rot based on Duncan's multi-range test, Ivano, Boomrang, Flores and Tous had the lowest rot index among the cultivars with the average index of 2.58, 2.65, 2.72 and 2.75 respectively and were introduced as resistant cultivars to the disease. Cultivars Jolgeh, Rasool, Shirin and Jam were categorized as susceptible.

Plant diseases, particularly diseases caused by fungi and oomycetes pose significant challenges in modern agriculture worldwide. Pathogen associated molecular pattern (PAMP) like chitin found in the cell walls of fungi and oomycetes, trigger defence signalling, leading to expression of R-genes and the production of reactive oxygen species (ROS), and accumulation of a wide range of metabolites. Chitin elicitors prompt the expression of defence-related genes such as chitinases, ultimately the resulting in the breakdown of chitin in the pathogen's cell wall. To assess the expression level of certain chitinases in potatoes and the activity of antioxidant enzymes, leaves of a tolerant potato genotype (jelly) was challenged with chitin oligomers in vitro. Result of this study revealed that 48 hours post chitin induction, the expression of different classes of chitinase genes were significantly increased. Class I chitinase (Soltu.DM.10G017450) and class III chitinase (Soltu.DM.11G026160) genes, had respectively the highest (5.5-fold relative to control) and the lowest (1.1-fold relative to control) expression level after 48 hours post chitin inoculation. However, the activities of antioxidant enzymes catalase and ascorbate peroxidase did not change significantly compared to the control. These findings suggest that the application of chitin does not activate the signaling pathways involved in the biosynthesis of antioxidant enzymes 48 hours after chitin treatment. In addition, results of this study may imply that chitinase genes can be cloned by genetic engineering approaches to generate transgenic plants resistant to pathogens.

Understanding the way of introduction and establishment of plant pathogens is essential to prevent new invasions. Most studies carried out in the last decade indicate that biological invasions are the result of the bridge-head effect. In other words, pathogens use a new environment or a new host plant as a primary base from which they can invade and cause epidemics in a proper time. Bridge-head effect has been observed with plant pathogens such as bacteria, fungi, and oomycetes in urban trees. Urban landscapes are usually the first point of contact of exotic novel pathogens with endemic plants, which is often due to the concentration of human activities and the introduction of exotic plants in these areas. Urban trees are a suitable location for the establishment of invasive pathogens which have been accidentally arrived at the area. Bridge-head effect probably plays a significant role in causing long-term damages and cause costly attempts for the management of plant pathogens. In contrast, for early detection of novel or invasive pathogens, one may use urban trees as sentinel plantings and the damages caused by these pathogens could be managed by prediction of the disease occurrence. There are some evidences for the existence of the bridge-head effect for oomycetes in urban trees and ornamental plants in Iran. Moreover, there are some reports indicating the existence of novel pathogens in these areas. The aim of this article is to review the aspects of the bridge-head effect in plant fungal and oomycete pathogens as well as planning to manage the potential threat to Iran’, s natural ecosystems caused by their bridge-head effects.