جستجوی مقالات مرتبط با کلیدواژه « blight » در نشریات گروه « گیاهپزشکی »

The Caspian boxwood (Buxus sempervirens subsp. hyrcana) trees are endangered, evergreen and endemic species in the Hyrcanian forests areas of northern Iran growing in Guilan, Mazandaran and Golestan provinces. This protected evergreen trees species is considered a unique and genetically valuable forest resource for Iran. The habitats of this valuable species, which is located in the lowlands, like other similar trees, always faced with overharvesting problems. But in addition to excessive harvesting, box tree moth Cydalima perspectalis and boxwood blight disease caused by the pathogen Calonectria pseudonaviculata (also known as box blight or buxus blight), as growing problems, are additional causes of boxwood habitats degradation. the outbreak of caspian buxus die-back due to boxwood blight disease was first reported in the summer of 2012 in the buxus forests located in the north of Iran and quickly infected more than 70% of the boxwood forests in the northern part of the country. Since then, there was intense concern that this disease might be the end of boxwood plants, and due to the importance of the subject, various research projects were implemented in research centers and universities in Iran, like other countries in the world. Currently, processes related to biodiversity protection of Hyrcanian boxwood are performed by Natural Resources and Watershed Management Organization as the best protection strategies, in which there are two protection strategies (in situ/ex situ) with different techniques. As the current approach to disease management in the world largely depends on the use of tolerant cultivars, research into boxwood blight resistance continues, so new resistant cultivars continue to be introduced worldwide. However, despite the importance of Caspian boxwood trees, there are no such studies in Iran. The objective of this study was to fill this knowledge gap by evaluating possible hyrcanian buxus accessions resistant to boxwood blight as a further step in improving the effectiveness and efficiency of this species protection management in the conditions of re-facing with the disease. Results of this study will enable growers and landscapers to better manage box blight disease.

In order to investigate the resistance of boxwood accessions from hyrcanian Forest areas of northern Iran to blight disease, infected boxwood habitats were visited in Golestan, Mazandaran and Gilan provinces, and to find boxwood plants with natural resistance, healthy buxux seedlings were collected from these habitats. Because in these types of studies, the process of resistance assessment begins by searching in natural forests for trees that remain healthy relative to their counterparts after exposure to an interest pathogen. In order to ensure buxus seedlings health, the seedlings that were collected from 12 boxwood forest habitats were kept for six months in the Alborz Research Complex (affiliated to the Research Institute of Forests and Rangelands of Iran) and their health was monitored. Finally, from the seedlings of each habitat, the freshest and most equal-sized seedlings were selected and used for greenhouse evaluations. In order to prepare the inoculum from the disease-causing fungus, the combination of four isolates of C. pseudonaviculata species, which had appropriate genetic diversity based on previous studies, was used. Seedlings were inoculated through foliar spraying of fungal spores (1× 105 spores/ml). Three weeks after inoculation, the average number of spots created on the stem and leaves of each boxwood plant as well as the average diameter of the largest leaf spot for each boxwood accession were recorded and analyzed.

The results of inoculation of blight pathogen on boxwood accessions showed that there were similar results in measuring the diameter of the leaf spot with the number of blight spots in each accession, so that, in plants with a higher number of blight spots, there was also a larger diameter of the leaf spot. Also, the results showed that although no accession is completely resistant to this disease and the disease appeared with different degrees in all accession; but a number of accessions are less sensitive to boxwood blight and the disease occurred in them with a lower severity. These results suggest to breeders to find natural resistance or create resistance in boxwood plants against blight disease through breeding programs.

In this study, for the first time, the resistance of different accessions of Buxus sempervirens subsp. hyrcana from boxwood habitats in the north of the country (as the only native and endangered boxwood species of Iran) to blight disease was evaluated. Based on the obtained results, it was determined that some degrees of disease tolerance can be found among different Hyrkani boxwood accessions. These results show that there is potential for plant breeders to select and recommend less susceptible boxwoods or to develop cultivars with improved resistance to boxwood blight.

The outbreak of boxwood blight disease caused by Calonectria pseudonaviculata in the Hyrcanian forests has led to efforts to find effective methods to control the disease. Biological control of the disease by beneficial microorganisms is one of these measures. In this regard, the present study was carried out in a completely randomized design with four replications at both laboratory and greenhouse levels. First, the antagonistic activity of 15 Bacillus isolates against the fungal pathogen was investigated using the dual–culture test, and the superior isolates (FRBP2, FRBS9, FRBS10, and FRBS15) were identified using standard biochemical tests at the species level. Tebuconazole and Serenade® were used as chemical and biological controls, respectively, according to their relevant instructions. The effect of the superior isolates’ suspension (108 CFU/ml) on the severity percentage of boxwood blight disease was evaluated under greenhouse conditions. Among the isolates, the highest (76.4%) and the lowest (26.5%) inhibition of the fungal colony growth was related to B. subtilis FRBS9 and B. pumilus FRBP2, respectively. In greenhouse conditions, B. subtilis FRBS9 and B. subtilis FRBS10 caused the lowest disease severity and showed no statistically significant difference with Serenade® (P<0.05). Thus, isolates belonging to the same or different species of Bacillus showed different levels of antagonistic activity against the target fungal pathogen. These isolates were able to control the fungal agent of boxwood blight through antibiosis and the production of a range of antibiotics. But more studies are needed to find their other antagonistic mechanisms and prepare their appropriate formulations.

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.

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.

The symptoms of bacterial leaf spot and blight on onion (Allium cepa L.) plants were observed in Fars (Eghlid) and Kermanshah (Bistoun) provinces with the rate of occurrence varying from 90 to 100% of the plants. In order to isolation and identification of the causal agent, suspicious samples were collected from infected fields. By culturing the samples on nutrient agar medium, 30 bacterial isolates were obtained. Pathogenicity test of the isolates on Allium spp. was performed and their pathogenicity was proved on onion, spring onion and leek. The isolates showed an identical total cell soluble protein pattern in SDS-PAGE. The isolates were similar to Pseudomonas syringae pv. porri based on phenotypic characteristics such as production of fluorescent pigment in KB medium, LOPAT tests, and utilization of different carbon sources. Genomic profiles generated with BOX-PCR placed the isolates into one groups. The results of the amplification and sequencing of the 16S rRNA, gyrB, and rpoD genes showed that the isolates belong to P. syringae pv. porri. This is the first report of the presence of the P. syringae pv. porri in Kermanshah province. Management of the disease seems to be necessary to prevent the disease epidemy.

Hyrcanian boxwood which is one of the evergreen shrubs is native of northern forests of Iran. Blight disease caused by Calonectria pseudonaviculata is one of the most important diseases of this plant, which causes severe leaf loss and decline in susceptible cultivars. This disease has been reported from the forests of Gilan and Mazandaran provinces. The history and importance of the disease, geographical distribution, disease symptoms, pathogen characteristics, the disease cycle, and the methods for disease prevention as well as the mechanical and chemical control measures are described.

Blight, caused by Mycosphaerella rabiei is the most important disease of chickpea in Iran. In order to find a method for the biological control of the disease, the inhibitory effect of 36 isolates of three species, Trichoderma harzianum, T. virens and T. atroviride, on a most virulent isolate of the pathogen, in hyperparasitism, dual culture, and production of volatile antibiotic compounds were investigated in vitro. Then the impact of the nine selected isolates of Trichoderma on the disease severity and growth of chickpea were tested in greenhouse. The results showed that the inhibitory ability of mycelium growth of the pathogen by isolates of T. harzianum, up to 52.42%, were greater than the others in plate assay. Also they had greater ability in reducing of disease severity in greenhouse condition. Some isolates of T. harzianum and T. atroviride had ability to promote the growth of chickpea in the presence of the pathogen with no significant difference as compared with the healthy control. It is the first report of the ability of these Trichoderma species in the biological control of this disease on chickpea.

Rice aggregate sheath spot disease is caused by Rhizoctonia oryzae-sativae (Sawada) and occurs more or less at all paddy fields in Guilan province. In this study some aspects of biology of Rhizoctonia oryzae-sativae and optimal growth temperatures were examined. Rice straw colonized with mycelia and sclerotia of Rhizoctonia oryzae-sativae were incubated in different field conditions such as natural field soil surface, 5 cm deep under the soil, flooding condition, on soil surface at the borders of the field. The effects of variable conditions on viability of fungus were studied. Moreover, the effects of different temperatures (5, 0, -5, -10, -15, -20 and -72) on germination and viability of sclerotia were assessed during one month. Optimum growth rate was found to take place at 32 ºC. Results showed that R. oryzae-sativae overwinters as mycelia on the rice straw on the soil surface in the field, soil surface at field margins and as sclerotia in the soil. According to the results 30.4% of sclerotia were able to germinate after one month storage at minus 72 ºC.

Early blight is an important worldwide disease of tomato that farmers must have frequent spray chemicals to control it. One way to reduce the use of pesticides, costs of production and the risk of environmental pollution, spraying based on forecasting of TOMCAST system, which is based on the time of wet leaves and temperature during tomato growing season in each region, predict disease severity, and determine suitable time of spraying. Application this system, in some countries considerably reduced pesticides usage on tomato. This system predict time of spraying when needed and has maximum effect. By using this forecasting method in Iran, can reduce pesticides usage on this freshly consume fruit, efficiency of using pesticides, and increase yield.

Cultivation of bell-pepper has been developed in Esfahan province, due to its nutritional value and consumption amount. In a survey, fields and greenhouses investigated for foliar diseases of this plant and diseased plants were collected. The collected plant materials were kept in clean plastic bags and transferred to lab. Studying the diseases symptom and isolation, purification, and morphological characterization of pathogens, five common diseases of aerial parts of bell-pepper including downy mildew, powdery mildew, Sclerotinia stem rot, Alternaria blight and gray mold, were identified. Causalfungi were Peronospora tabacina, Levielulla taurica, Sclerotinia sclerotiorum, Alternaria alternate and Botrytis cinerea, respectively. Methods of sampling, isolation and purification of pathogens, diseases symptoms and morphological characteristics of pathogens illustrated.