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

Sheath blight (ShB) caused by the soil-borne fungus Rhizoctonia solani AG1-IA is one of the most important diseases of rice in the world, which is also common in some areas of rice cultivation in Iran. The pathogen usually overwinters as sclerotia in soil and plant debries and mycelium in plant debris and seeds. Sclerotia can survive inactive in soil, and rice debris for several years. After transplanting susceptible rice cultivars, the sclerotia germinate, produce mycelium, and infect the lower sheaths of the rice plant. The characteristic symptoms of ShB are green-gray water-soaked lesions, spherical to oval, or irregularly discolored on rice sheath. The lesions are connected, and the center of the lesions becomes gray to light brown with a dark brown-to-red border, by passing time. Factors such as the rice variety, plant density, and growth stage, initial inoculum population of the pathogen, environmental conditions, and plant nutrition affect the disease severity and epidemic. The disease management is difficult, because of the wide host range of the pathogen, its ability to survive for a long time in the soil, and the low level of resistance of rice cultivars to it. Proper management such as avoiding cultivation of dwarf and high tillering cultivars in fields with a history of pathogen presence, seed disinfection, proper plant densities, and optimal use of nitrogen fertilizer, field sanitation, and chemical control can prevent the epidemy and damage of the disease.

Turf grass is the most important grown plant in urban green space, which functions such as temperature adjustment, increase in relative humidity, air softness and dust absorption. Fungal and fungal-like diseases are the most common lawn diseases in Iran, affecting this plant at all stages of growth, causing its decline. Pythium, Fusarium, Microdochium, Rhizoctonia, Bipolaris, Pyricularia and Colletotrichum species are known as damping-off, root and crown rot, leaf spot and anthracnose pathogens of lawns in Iran. The symptoms of these diseases, the morphological characteristics of pathogens and the methods for their management are described.

Damping-off caused by Rhizoctonia solani J. G. Kühn is a very important plant disease among soil-borne diseases that make severe damages on a wide range of plants in the world. Biological control of this disease with Trichoderma, Gliocladium, Bacillus, Pseudomonas and Rhizobium species has been reported as a successful management method. The results of some researches on this area and the mechanisms of the effect of these antagonistic fungi and bacteria are described here.

Rhizoctonia root rot which is caused by Rhizoctonia solani Kühn, seriously reduces the yield of bean. To prevent the widespread distribution of the disease in the main bean growing regions, it requires accurate identification of the effecting factors on disease occurrence and prevalence. Due to the lack of resistant cultivars and ineffectiveness of the chemical measures in the soil, the cultural practices play an important role in disease control. According to the findings, increasing the organic matter, improving the activity of nodule-forming rhizobia on root, avoiding of bean cultivation in sandy soils, maintaining the neutral pH level of soil, irrigation at 7-9 days interval in growing season, planting with a standard density of 30 plants per square meter, seeding at depth of 5 cm in the warm and dry climatic conditions, sprinkler irrigation, kidney beans growing in the infected fields, appropriate rotation program, applying maximum 50 kg urea /ha, weed control, seeder machine adjustment, soil application of fungicides and seed treatment with proper systemic fungicides should be considered in an integrated management program. Proper application of rhizobacteria can effectively reduce the use of chemical fertilizers as a complementary control measure.

During a survey in the years 1384-1386 from olive orchards in Khuzestan province, a sample of olive trees showing symptoms viz wilting, dieback and in some cases decline was collected. After washing and surface sterilization, the suspected samples were cultured on PDA medium and incubated at 25 ° C. In total, 124 fungal isolates from root and crown of olive were identified including a species from Verticillium (V. dahliae with 35 isolates), three species of Fusarium (F. solani with 23 isolates),) F. equiseti with 20 isolates), (F. semitectum with 4 isolates), three species of Cylindrocarpon (C. destructans with 20 isolates), (C. didymum with 8 isolates), (C. obtosisporum with 9 isolates), and R. solani with 5 isolates that were multinucleate and belonged to anastomosis group AG-4. The pathogenicity test of V. dahliae, F. solani, F. equiseti and C. destructans isolates were performed on olive seedlings 12 months by dipping the roots of seedlings in spore suspensions while R. solani isolates pathogenicity test was performed on a 12 -month-old olive trees and wheat. Results of pathogenicity tests showed that the isolates obtained from three species including F. solani, V. dahliae and C. destructans were as strongpathogens, F. equiseti as moderate pathogenic and R. solani as weak pathogen on olive. This is the first report of species F. equiseti and C. destructans on olive in Iran and species F. semitectum, C. didymum and C. obtosisporum as the olive pathogens.

Mungbean (Vigna radiate (Wilczek)) because of having high protein content, short geowing period and good tolerance to high temperature is one of the most important pulse crops in tropical and sub tropical regions. Mungbean is widely planted in Khuzetan province and the area under its cultivation in Khuzestan is significantly more than any other provinces in Iran. Fungal diseases of root and crown of this plant are among its important diseases worldwide. In this investigation, distribution and identification of the causal agents were studied. During summer and fall of 2010 and 2011, 78 samples were collected from Mollasani, Dezful, Shushtar, Abbid, Gotvand, Ramhormoz and Susangerd which are the main Mungbean cultivation areas in Khuzestan. Macrophomina phaseolina, Rhizoctonia solani and Fusariun solani were recovered from these samples. The collected data illustrated that M. phaseolina with the occurrence frequency of 70.51% was the main cause of the disease. R. solani with 17.95 and F. solani with 11.54% occurrence frequency belonged to a statistically separate group. Moreover, the reaction of the M. phaseolina isolates to potassium chlorate was studied. According to the results, the Macrophomina isolates were divided in two groups, chlorate sensitive to 77.3% and chlorate resistant to 22.7%. Among the chlorate sensitive isolates, two phenotypes - feathery and restricted growth- were identified while the phenotype of chlorate resistant isolates was dense growth. Statistically investigation into pathogenicity of different phenotypes of Macrophomina isolates showed that chlorate resistant isolates with dense growth intensively made infection and sensitive isolates with feathery phenotype ranked second, and sensitive isolates with restricted phenotype had the least pathogencity.

Rhizoctonia canker, also known as stem canker and black scurf of potato, Rhizoctonia solani Kuhn, causing serious economic losses by canker on under ground stem, roots, stolens, blanding of tubers and black scurf on potato surfacee in Isfahan. In this manscript, the effects of green chitting and or disinfection of potato seed tubers and soil were considered on this disease in the fields. The laboratory trails on R. solani isolates indicated that, almost all the sclerotinia are pathogenic. The seed tubers of four potato cultivars were selected and kept under room temperature along with normal light and high humidity for two months. Then, they were sown in the highly infested soil to the disease. The results indicated that the green chittings reduced Rhizoctonia stem canker severity effectively. In comparison to the above experiments, the fungicide screening, Rovral in the form of seed, soil and simultaneous seed and soil applications were carried out in the same fields. The results showed that the stem canker severity was reduced effectively compared to chittings and that of control. Increased growth response was observed in only green chitted potato seed tubers compared to other treatments.