نشریه تحقیقات بیماری های گیاهی
سال پنجم شماره 2 (پاییز و زمستان 1396)

The casual agent of tobacco black shank disease, Phytophthora nicotianae Breda de Haan (=P. parasitica Dasture), is one of the most important pathogen in tobacco fields. Disease can occur at all stages of plant growth and damage can occasionally reach up to 100% in some fields. In order to determine the status of the disease in tobacco fields of Golestan province, 45 tobacco fields were selected in five different village of Gorgan regions (Taghartappeh, Jafarabad, Ghorogh, Nodehmalek and Valeshabad) and in four different village of Aliabad regions (Pichakmahaleh, Baraftan, Fazelabad and Elazman) during 2014 growth season. The disease amount on aerial parts of tobacco plants was recorded during the infection period according to weekly surveys in the selected fields started when the primary symptoms become apparent. Statistical analysis was performed using the Stat Graphics Centurion XV software. The disease incidence was similar in different regions but there was significant difference (P

Wheat leaf septoriosis caused by Mycosphaerella graminicola is one of the most important and destructive diseases of wheat. Since the resistant cultivars are not durable, disease control is mainly based on using fungicides where the yield loss is considerable. But using one fungicide may cause resistance. In this study, the impact of falcon® fungicide on disease control of wheat septoriosis has been studied. The experiment is carried out by randomized complete block design with 4 replications at Khuzestan agricultural and natural resources research center. No fungicide treatment and Tilt® used as controls. Results of this study showed that Falcon® treatment had lower AUDPC, higher yield and thousands of kernel weight compared to control and Tilt®. Disease severity progress was similar in both Tilt® and Falcon® treatments. Based on the results of current study, Falcon® fungicide is a suitable alternative of Tilt® in periodic applications of fungicides to combat leaf septoriosis

With consideration to environmental risks and appearance of resistance in pathogens due to use of chemical pesticides, application of other managing measures such as cultural methods can be useful in controlling Rhizoctonia rot. This experiment was conducted to investigate the effects of potassium, silicon and vermicompost on controlling of Rhizoctonia rot (Rhizoctonia solani) of pinto bean. A factorial pot experiment with four replication was conducted in 2014 based on completely randomized design with three factors including potassium (0, 50 and 100 kg ha-1), calcium silicate (0, 400 and 800 kg ha-1) and vermicompost (0 and 5 % V/V). The results showed that main factors increased vegetative growth parameters of pinto bean and reduced the level of Rhizoctonia rot. So that, application of 100 kg ha-1 of potassium or 400-800 kg ha-1 of calcium silicate and vermicompost significantly increased vegetative growth (root and shoot) fresh and dry weight. The treatments also significantly improved biochemical characteristics such as the amount of gaiacol peroxidase. In general, our results showed that plant nutrient greatly improved plant vegetative parameters and plant resistance to biotic stress. Accordingly, we found that the use of calcium silicate (400 and 800 kg. ha-1) and 100 kg.ha-1 of potassium had highest effect on controlling Rhizoctonia rot and improving plant vegetative growth.

Fusarium wilt disease of Iranian chickpea caused by Fusarium oxysporum f.sp. ciceri fungus is one of the most important chickpea diseases in Iran. In order to study the genetic diversity of this pathogen, 47 isolates were collected from infected areas in Ilam province. After extracting DNA, the genetic diversity of these isolates was analyzed using ISSR molecular markers. Based on the results at the level of 64% similarity coefficient, isolates were clustered into 24 groups. This result demonstrates the high genetic diversity among the isolates in Ilam province. Based on information obtained from ISSR primers were among six studied populations, the highest genetic distance was found to be 0.054 between Sarableh and Sirvan populations and the lowest genetic distance as 0.010 between Asemanabad and Shabab populations. Gene flow and genetic differentiation using Pop GEN software showed that gene flow is related to ISSR5 with its amount as 18.27 and the lowest value was related to ISSR7 with its amount as 1.65 and the mean gene flow was calculated as 4.60. In this research, the mean flow was 0.098. The calculated genetic variance was 6% between the populations and as well as to be 94% in populations. High genetic variation between and among populations shows the potential different aggressiveness of isolates. This shows the importance of the dominant pathotype(s) identification in the region as well as using them in the process of introduction new resistant cultivars.

Sclerotinia sclerotiorum is an important phytopathogen causing tobacco collar rot which distributed worldwide and can impose high yield losses in tobacco growing countries. The disease management is possible by use of fungicides, resistant cultivars, biological control and use of plant extracts and essential oils. Crude extracts of catmint (Nepeta cataria), tobacco (Nicotiana tabaccum) and thyme (Thymus pubescens) were prepared by water, acetone, hexane, ethanol and methanol with concentrations of 1000 and 2000 ppm. The effect of those extracts against the fungus was examined in vitro in a factorial experiment based on completely randomized design with three replications. Minimal inhibitory concentration of extracts was determined by agar diffusion method. Crude extracts of tobacco, catmint and thyme had remarkable antifungal activity. Hexane, ethanol and methanol were the best solvents to extract antifungal compounds. Minimal inhibitory concentration of hexane, ethanol and methanol extracts of catmint, tobacco and thyme were 1 mg/ml as tested on the fungus. The most important components of extracts of catmint were menthanol, menthol, sailen, thymol, pipertenone, nonenal, carvacrol, camphor and limonene; in extracts of tobacco, globulol, phytol, nicotine, sailen, imidazole, limonene and thunbergol; and in extracts of thyme, thymol, anethole trans, sailen, carvacrol, imidazole and nonenal. Therefore, extracts of catmint, tobacco and thyme can be considered as natural fungicides for control of causal agent of tobacco collar rot.

Prune dwarf virus (PDV) belongs to the genus Ilarvirus, Family Bromoviridae. This virus is one of the most important pathogens of stone fruit trees worldwide. To detect and determine the distribution of Prune dwarf virus in the orchards of stone fruit trees in Fars Province, 679 leaf samples showing symptoms of deformation, twisting and mosaic were collected from peach, plum, apricot and almond trees during two crop years, 2014 and 2015. The samples were tested by DAS-ELISA for the presence of PDV. The results of ELISA test showed that nearly all of the orchards are infected (213 out of 679 samples). According to the results, infection percentages were 19.1%, 45.92%, 10%, 38.57%, 21.05%, 9.23% and 10.71% in Shiraz, Kavar, Jahrom, Zarghan, Sepidan, Neyriz and Sarvestan, respectively. Also, infection percentages among symptomatic samples were 46.07, 14.52, 38.75, 9.84 and 5.45% in peach, nectarine, plum, almond and apricot, respectively. This is the first report of Prune dwarf virus from Fars province and nectarine as host from Iran.