جستجوی مقالات مرتبط با کلیدواژه « powdery mildew » در نشریات گروه « گیاهپزشکی »

Within the framework of the Mycology research laboratory's program at the University of Guilan focusing on the identification and DNA barcoding of powdery mildew fungi (Erysiphaceae, Ascomycota) from Iran, a powdery mildew specimen on Helichrysum was collected from Zanjan-Tarom road and subjected for morphological and molecular identification. Although this species morphologically resembles Leveillula helichrysi, and some other closely related species such as L. taurica complex, the ITS sequence differentiates this fungus from the sequences of L. helichrysi and L. taurica available in GenBank. We suggest this collection may represent a new species or new haplotype within L. helichrysi. Therefore, until we obtain more samples and sequence the type material, we report this fungus as Leveillula cf. helichrysi from Iran.

Powdery mildew of wheat caused by Blumeria graminis f.sp. tritici, is one of the most important and common wheat disease in humid, semi-humid and semi-arid regions of the world, including Iran. At present, one of the important aspects of the management of this disease is its chemical control. In this study, the efficacy of the Pilartep (Tebuconazole +Pyraclostrobin) SC 30% was evaluated in controlling the powdery mildew of wheat in three regions of Qarakheil and Bayekola (Mazandaran) and Kohnekand (North Khorasan province) regions based on randomized complete block design with six treatments and four replications. Experimental treatments included Pilartep (SC 30%) 0.4, 0.5, 0.6 and 0.7 l/h, Tilt (EC 25%) 1 l/h, Folicur (EW 25%) 1 l/h and control. Spraying operation was performed in the growing stage of stem emergence with the emergence of flag leaves. The plots were evaluated for disease incidence and severity percentage using double digit scale and at the end of the season, wheat yields were recorded for each plot. In evaluating the effect of fungicides on incidence, disease severity percentage and crop yield, Pilartep fungicide at the rate of 0.6 and 0.7 l/h was placed in the first statistical group (the highest group). In general, according to the results obtained in order to use the fungicide optimally, Pilartep (SC 30%) at the rate of 0.6 l/h is recommended in the control of powdery mildew of wheat.

Powdery mildew and Leaf stripe diseases are the most important of barley fungus diseases in Iran. Identification of new genetic resources and breeding for resistance is one of the most economical and adaptive methods for controlling these diseases. Therefore, the aim of this study was an identification effective molecular marker for detection Rdg1a and mlo resistance alleles for Marker Assisted Selection against two diseases Leaf stripe and powdery mildew.

This study was conducted on F2 population derived from crosses the RIL-27 that has Rdg1a, mlo-11 resistance alleles and Yousef which has susceptible alleles (rdg1a, MLO). The RIL27 line is one of the lines of the recombinant inbred line population that derived from a cross between the VADA cultivar and the L94 Ethiopian line. 60 samples of F2 population were divided into two populations of 30 for genotyping and phenotyping against two diseases. We used HVCSG and mlo-6 and mlo-10 markers for the presence detection Rdg1a and mlo-11 respectively. Also Manchuria cultivar, which is susceptible to powdery mildew was used to produce inoculum powdery mildew. Genomic DNA of the plants was extracted from non-infected leaves in a two-leaf stage by using the CTAB method. Then, the quantity and quality of extracting DNA were studied by using (Thermoscientific (USA)) and Agarose gel (1%). The HVCSG, mlo-6 and mlo-10 markers amplified fragments 705, 440 and 380 base pairs respectively. Phenotyping evaluation against P. graminea was performed by using the sandwich method and for phenotyping evaluation against B. graminis was done using Aghnoum and et al method. And then the percentage of infect plants were counted.

In this study at first, HVCSG marker was used to distinguish Rdg1a resistance allele in parents and F2 population. This marker amplified the 705 base pair band that the result obtained was corresponding to what Biselli and et al showed in 2010. Biselli et al. Developed the HVCSG molecular marker to identify the Rdg1a resistance allele in the RIL population from the VADA × L94 crosses by rice EST sequence and they said, this marker amplifies the region from 4500 to 5025 sequences encoding the Shalcone synthase gene. But in this study, the results of using this marker in the F2 population are completely inconsistent with what Biselli and et al have stated. The results show that the HVCSG marker has a low efficiency. Second to check and confirm the presence of mlo-11 allele of mlo-6 and mlo-10 markers were used. The size of amplified regions (440 of the mlo-11 gene and 380 base pairs of the MLO gene) was corresponding to the results of Reinstadlr and et al. showed that these markers amplified 380 and 440 base pair fragments. After of inoculation test and the appearance of the symptoms of the diseases the percentage of infect plant for phenotyping against leaf stripe disease was counted. The Yousef cultivar, which was infected with P. graminea as a susceptible parent, showed success in the inoculation test. In other samples, 24 days after planting, symptoms of leaf stripe disease appeared in the five leaf stage. First, on the infected leaves, a yellow strip appeared, and most of the leaves that were later formed showed signs of the disease. Then the yellow strips on the leaves infected joined each other and caused the death of the leaf. Two resistant parents, RIL27 and VADA showed very low symptoms of leaf stripe disease. The results of inoculation test in this study was corresponding with studies from Arru and et al (2002) and Biselli and et al (2010). Arru et al showed that VADA was showing very little about 7% of the symptoms disease due to the presence of the resistance gene. Biselli and et al (2010) also reported that the percentage of infections in VADA parent is 2%. For phenotyping evaluation against powdery mildew disease after infecting the seedlings with B. graminis fungus, in the Yousef parent, symptoms were observed as white fluffy dots on the leaf surface. In the VADA variety, there were necrotic points. L94 and RIL-27, which had mlo-11 resistance gene, did not show any symptoms of the disease. L94 is a native Ethiopian cultivar that allele carries mlo resistance, so it is resistant to powdery mildew. The F2 population showed different signs based on the presence and absence of allele resistance. The samples with resistance allele, there were appeared mildew cholestasis and necrosis symptoms, and those that did not have resistance alleles were appeared necrotic and fluffy symptoms. In mlo-11 resistance alleles, the necrotic symptoms can be due to the presence of the Ml (La) resistance gene and also the pleiotropy effects of the molecular gene. Xintian et al reported that the mlo genes were not without pleiotropic effects, and necrotic symptoms on leaves of plants with mlo-11 resistance gene could be due to the effect Overlapping of the mlo gene with other QTLs. Conventional plant breeding methods are based on phenotypic selection of superior genotypes in segregation generation. Phenotyping methods are often costly and time-consuming for specific traits, but Marker Assisted Selection (MAS) is one of the methods developed to prevent of common problems in conventional plant breeding techniques. In some studies, the researchers pointed to use of molecular markers for facilitating of plant breeding programs.

Molecular markers are used as a new tool for increasing the efficiency of breeding programs to identify genetic resources. In addition, shortening the duration of breeding programs and the selection of recessive alleles, the molecular markers helps to facilitate the pyramiding of resistance genes to provide a broad and durable resistance. In general, the development of efficient molecular markers and the identification of different genetic resources against plant diseases and the pyramiding of resistance resources are preventing of the increasing use of chemical pesticides and fertilizers to control the pathogen.

The purpose of this study was to evaluate the efficacy of Cyflufenamid 3.4% + Triflumizole 15% Pancho® TF (WG 18.4%) fungicide in controlling of peach powdery mildew. The field trials were undertaken on Esfahan, Markazi and Kohkiloyeh va Boyerahmad provinces. Three commercial orchards of susceptible cultivar (Alberta) which had a background of contamination to the disease in previous years and the trees were almost at the same age, base and growing conditions, were selected. The experiment was carried out in a randomized completely block design pattern with six treatments and four replicates. The fungicides included: Pancho® TF (WG 18.4%), 0.5/1000, 0.75/1000, 1/1000, Kresoxim-methyl 100g/l + Boscalid 200g/l (Collis® SC 30%), 0.5/1000 and control with water spraying and control with no spraying. Fungicides were used at swelling flower buds stage, the end of flowering time and three weeks later. The sampling was carried out of leaves and fruits, three weeks after the end of spraying the parameters of severity disease percent and incidence disease percent were assessed based on available scales considered and the data were analyzed using SAS software. The results showed that there was significant difference between treatments (fungicides) and controls at 1% probability level.  Mean comparison of the treatments with Duncan Multiple Test at 5% probability level showed that, all fungicides caused a significant decrease in the severity and incidence of disease infection percent compared to controls. The results of data analysis in three regions showed that Pancho® TF, 0.75/1000 with 69%, 67% and 71% on leaves disease severity and with 69%, 58% and 74% effect on leaves disease incidence in Esfahan, Markazi and Kohkiloyeh va Boyerahmad provinces respectively, had the best effect in controlling peach powdery mildew. Beside, Pancho® TF 0.75/1000 with 67% and 78% effect on fruits disease severity, 74% and 76% on fruits disease incidence had the best effect in Markazi and Kohkiloyeh va Boyerahmad provinces respectively. So Pancho® TF, 0.75/1000 is recommended to be used in peach powdery mildew management.

Efficacy of difenoconazole+cyflufenamid (Cidely-Top® DC 14%) in control of cucumber powdery mildew, caused by Golovinomyces cichoracearum was evaluated using RCBD with 6 treatments and 4 replications in Alborz, Tehran and Khuzestan provinces. Treatments included 0.8, 0.9 and 1 ml L-1 of Cidely-Top®, tetraconazol (Domark® EC 10%) 0.4 ml L-1, bicarbonate potassium (Kaliban® SL 85%) 5 g L-1 along with no spraying control. Foliar sprayings started once early symptoms appeared and followed up at 5-10 days intervals. The data noted before each spraying and 14 days after the last spraying as the DSI by using Horsfall and Barrat scale from 1-7. Mid-point was using for each plant. AUDPC was calculated for each plot, too. Data were analyzed by SAS software and means were compared using DMRT (P=5%). Comparison of the efficacy of treatments based on the AUDPC which displays cumulative percentage of disease during a 36 days period revealed that Cidely-Top®  0.8, 0.9 and 1 ml L-1 have reduced the AUDPC by 74.9%, 81.2%, and 85.2% respectively in comparison with the control. Meanwhile, the Domark® at the rate of 0.4 ml L-1 resulted in the efficacy of 82.7% and Kaliban® also showed the least amount of efficacy (59.8%) compared with the control. Based on the results obtained from this research, the fungicide Cidely-Top® may be recommended to be used at 0.8 ml L-1 for 5 to 7 days intervals, at 0.9 ml L-1 for 7 to 10 days intervals and at 1 ml L-1 for up to 14-days intervals.

Barley is one of the most important cereals in the world after corn, wheat and rice. Powdery mildew is one of the important fungal parasites of the plants which cover their above ground parts with the formation of a white fungal vegetative organs causing yellowing, drying and reducing the quantitative and qualitative traits of the field crops, fruit trees and ornamental plants. In order to locating the powdery mildew resistance QTLs in the F3 generation derived from the cross Badia and Kavir cultivars, a population consisted of 104 families was cultivated in 2017 at Gonbad-e-Kavos University. To provide a genetic map, several groups of markers including of 28 SSR, 9 ISSR, 3 IRAP and 5 iPBS (93 alleles) that were related to barley chromosomes used. Genetic maps were covered 617.5 cM and the mean gap between flanking markers was 5.41 cM. Four QTLs were detected on chromosomes 3, 4 and 6 to powdery mildew resistance. The results of this study led to a new QTL trace for the desired trait. The QTL qSPM-4b with LOD=3.26 that was between the two ISSR13-1 and ISSR16-4 markers, controlled 13/.6 of the phenotypic variations of the respective attribute with an incremental decrease of 0.12. The QTLs detected could be used in breeding programs to increase the resistant sources against the disease and to increase the yield of the new produced cultivars. The results of the current research can be used in breeding programs after determining the validity of markers.

Cucumber is one of the economically important vegetables in Iran which is extensively attacked by powdery mildew. Identification and application of disease resistant genotypes is an efficient method to escape the disease epidemic. A number of 23 greenhouse and field cucumber cultivars were evaluated and screened for powdery mildew resistance and putative resistant cultivars were identified based on percent Disease Index (PDI) measurement. In addition, leaf chlorophyll fluorescence was measured and analyzed in 5 cultivars selected from resistant, semi-resistant and sensitive groups. Based on the results of PDI measurements, a considerable variation between the cultivars was observed so that the cultivars classified to four groups including resistant, semi-resistant, semi susceptible and susceptible. Two greenhouse cultivars i.e. CLE and Green Magic with the PDIs of 7.78 and 8.33 were the most resistant and the two field cultivars Beit Alpha and SuperN3 with the PDIs of 31.11 and 31.67 were the most susceptible cultivars. Based on the ANOVA of chlorophyll florescence parameters, a significant infection effect on minimal florescence (Fo), variable florescence (Fv) and vitality index (Fv/Fm) and a significant genotype effect on Fo parameters was observed (P

Plant disease can cause quality and quantity reduction of agriculture crops. In some countries farmers spend considerable time to consult with plant pathologists, whereas time is an important factor to control disease, so it seems to offer a fast, cheap and accurate method to detect plant diseases. Since the fungal disease named ‘Powdery Mildew’ and ‘Anthracnose’ cause the greatest amount of damage in cucumber produced in greenhouses, thus in this research the mentioned two fungal disease detection and classification were studied using image processing and neural networks technique. Image processing steps includes four main steps: 1) Image acquisition 2) preprocessing 3) extraction of the best color parameters of HSV and L*a*b* color spaces in order to classify and extract defected area of the leaf and 4) extraction of textural properties of defected area of cucumber leaf using co-occurrence matrix. Since, two factors of accuracy and time are important in detection and classification of plant disease, thus artificial neural networks (ANN) with back propagation algorithm (BP) and Levenberg-Marquardt (LM) training function was selected as the best model that was able to successfully detect and classify mentioned plant diseases in 6 seconds with 99.96% accuracy.

Powdery mildew disease caused by Erysiphe necatoris one of the most important diseases of vine that cause quality and quantity damage in many parts of Iran every year. In the present study, the efficacy of new fungicide, imonoctadin (Belkute® WP 40%) was compared with common fungicides including penconazole (Topas EW® 20%), sulfur (Kumulus-S® WP 80%), and sulfur powder for the control of Powdery mildew disease on grape. The experiment was carried out in Semnan (Shahrood), Kohkiloye and Boveirahmad (Yasuj) and Qazvin provinces in a Randomized Complete Block Design (RCBD) with 8 treatments and 4 replications. Treatments included Belkute at 0.5, 0.75 and 1 g/l, Topas 0.125 g/l, Kumulus –S 3 g/l, sulfur powder 60 – 90 kg per/ha. (According to the first, second and third stages of spraying) and controls (without any spraying and with water spraying). Treatments were applied at three stages (the first spraying time was before swelling buds, second one was after petal fall and the third one was 2-3 weeks after the second spraying, which coincided with the appearance of sour grapes). Percent disease incidence and Percent disease severity were measured and analyzed using SAS software in three provinces. Mean comparison of disease severity and disease incidence percentages were done by Duncan's multiple range test (α =5%). Results show significant differences between all the fungicide treatments and the controls. Belkute at 1and 0.75 g/l alone or in alternation with Topas 0.125 g/l had better controlling affects than the other treatments. Percent disease severity (PDS) in vines treated with Belkute 1and 0.75 g/l were 6.95 and 6.72% on leaves and 29.99 and 33.33% on fruits in Semnan Province, 10.40 and 2.45% on leaves and 3.30% on fruits in both treatments in Kohkiloye and Boveirahmad Province, 9.56 and 29.56% on leaves in Qazvin Province respectively. Also, percent disease incidence (PDI), were 30.50 and 37.50% on leaves and 70.00% on fruits in both treatments in Semnan Province, 7.75 and 10.50% on leaves and 10.00% on fruits in both treatments in Kohkiloye and Boveirahmad Province, 42.75 and 50.86% on leaves and 85.00 and 70.00% on fruits in Qazvin Province respectively.

In this study, 224 wheat genotypes which had good agronomic characteristics were selected between 1700 collection of Cereal Research Department, Seed and Plant Improvement Institute, to evaluating against diseases FHB, leaf rust and powdery mildew resistance in field condition in Golestan province. After land preparation, seed of each genotype were planted on a line with length 1.5 meters below mist irrigation systems. Spikes at 50% flowering (stage 65 of the Zadoks) were inoculated with spore suspension of fungi isolates of Fusarium head blight (Fusarium graminearum, F. culmorum) within three days of one another in two stages. To evaluate genotypes resistant to leaf rust, in stem elongation (stage 35 of the Zadoks), were sprayed with a mixture of spores of the pathogen. Genotypes were evaluated to powdery mildew with naturally infected area. Notes the reaction of genotypes diseases mentioned above, the standard method of assessment for all diseases. The results showed that, 60 percent of genotype in disease incidence of Fusarium head blight were moderately susceptible and 30% were susceptible reaction and the rest were moderately resistant and resistant, but in disease severity FHB, 30% of moderately susceptible reaction, 37% susceptible and the rest were placed in resistant and moderately resistant groups. In the disease index FHB of genotypes showed that 20 percent moderately susceptible, 22% susceptible, 34% moderately resistant and 24 percent showed good relative strength. Results evaluated genotypes reaction to leaf rust races in the region showed that 43% resistant, 47% susceptible and others 10 percent were moderately resistant or moderately susceptible. In this study, 17% of genotypes were resistant, 25% moderately resistant, 27% moderately susceptible and 31% were quite susceptible. After analysis of the data, 20 genotypes were favorable partial resistance to any of the diseases studied, were introduced as sources of resistance and molecular genetics of resistance to genetic unit Cereal Research Department, Seed and Plant Improvement Institute.

In order to identify the species and host range of Erysiphaceae fungi in Ardabil province, infected plant specimens belonged to 47 plant species were collected during 2012-2013 and the species identified according to the new treatment available in taxonomy of this family. Totally, 32 species and 9 genera belonged to Erysiphaceae were identified and described. Among taxa, two species Erysiphe howeana and Neoerysiphe galeopsidis on Oenothera sp. and Ballota nigra were reported for the first time in Iran, respectively. Two species Golovinomyces cf. orontii and Golovinomyces macrocarpus were introduced as powdery mildew agent on Viola tricolor and Tanacetum balsamita in Iran, respectively. Previously these species were reported as Oidium violae and Erysiphe cichoracearum, respectively. Also, 19 species are new for Ardabil province mycoflora. Among 32 identified species in this study, 10 fungal species had infected more than one host plant that Blumeria graminis had the widest range with five host plant species.

In this study different characters of powdery mildew of alfalfa were investigated in natural resources around Boroujerd in Lourestan province. The fungi species, disease severity, ascospore as primary inoculums, percent of germination of conidia, chemical analysis of non-infected and infected plants, overwintering manner of fungi and correlation of plant phonologic period with fungi growth organs were studied. The fungi were identified as Leveillula taurica (Lev.) Arnaud. The mean of the disease severity on upper and lower leave surfaces was 12.13± 2.4 and 39.32± 3.81 percent, respectively. Between disease severity on upper and lower surface of leaves there was a positive and significant correlation (r= 46.4) & (p<0.01). Liberation of ascospore increased from bigining of liberation until infection time. It was determined that ascospore was the primary infection source. Also, the best temperature and time for germination of conidia was 100.C and 72 hour and there was not any statistically significant difference between 3 temperatures of 10, 15 and 200.C (p<0.01). Between dried mater and ether extract of non-infected and infected plants there was not any statistical significant differences, but between the crude protein, crude fiber and ash of non-infected and infected plant there was a significant difference (p<0.05). The growth of fungi on plant began 5 days after June. The mean height of plants was 55.25 cm and at green stage of plant and the sexual stages, the growth of fungi completed 6 days after the September when the seeds of plant fell on the ground.

Endomycorrhizal fungus Piriformospora indica protects host plants against biotic and abiotic stresses via induced systemic resistance. In the present study, the ability of this fungus to induce resistance in wheat against powdery mildew fungus (Blumeria graminis f. sp. Tritici, Bgt)was evaluated. Forty Iranian wheat genotypes were screened for sensitivity to wheat powdery mildew and Falat cultivar was selected as the most susceptible genotype. To investigate the expression patterns of PR1, PR2, PR5 and PAL defense genes, Falat genotype was colonized by P. indica and then exposed to Bgt together with non-colonized plants. Results showed peak expression of the resistance genes have at 24 hours after inoculation in both treated and control plants. The expression rate of the evaluated genes increased slowly in control plants but elevated earlier and higher in P. indica colonized plantsafter inoculation with Bgt. These results indicate that P. indica causes early and faster induction of plant defense genes and their elevation causes induced systemic resistance in plants. At 48 hours after inoculatin, transcript levels of early induced genes started to dampen in both groups of experimental plants, indicating effective suppression of defense-associated genes upon haustorium development.

In order to study the reaction of 23 different advanced wheat cultivars and lines against major foliar diseases in Golestan province، including powdery mildew، brown rust and tan spot، an experiment was conducted in a randomized complete block design with three replications during winter of 2009. Infection was created naturally in the field by planting susceptible rows between the treatments. Evaluation of the treatments was done based on the intensity of different diseases (disease incidence، disease severity، area under disease progress curve (AUDPC) and standardized AUDPC، total seed weight and thousand kernel weight (TKW). Analysis of variance showed that treatments were statistically different (P≤0. 01) based on all recorded data. Results of multiple range test (LSD) showed that the highest and lowest severity of powdery mildew were observed in line 17 (72. 74%) and Gaspard (0%)، respectively. The highest and lowest severity of brown rust was observed in Bolani and Morocco (11. 11%) and Gaspard (0. 12%)، respectively. The highest and lowest severity of tan spot disease was recorded in Morvarid (94. 56%) and Morocco (0%)، respectively. The highest grain yields were recorded in line 11 (4340. 97g) and Morvarid (4013. 19g)، and lowest grain yields recorded in Bolani (184. 03g) and Morocco (250g). The highest and lowest TKW were observed in Cultivars Shiroudi (36. 33g) and Morocco (13. 53g)، respectively

Many powdery mildew fungi occur as anamorphic state on different host plants in Guilan province، Iran. The species have usually been identified as Oidium spp. In order to identify teleomorphic species using anamorphic characteristics and host range، several infected plant specimens were collected from around Guilan province during 2004-2011. Based upon the results of the study 25 species were collected and identified. The identified species are as follows: Erysiphe cf. alphitoides on Quercus sp.، Erysiphe australiana on Lagerstroemia indica، Erysiphe begoniicola on Begonia multiflora، Erysiphe betae on Dysphania ambrosioides، Erysiphe convolvuli on Convolvolus sp.، Erysiphe euonymicola on Euonymus japonicus، Erysiphe heraclei on Petroselinum hortense، Erysiphe polygoni on Polygonum persicaria، Erysiphe platani on Platanus orientalis، Erysiphe quericicola on Quercus sp.، Erysiphe sesbaniae on Sesbania punicea، Golovinomyces ambrosiae on Zinnia sp. and Dahlia sp.، Golovinomyces artemisiae on Artemisia annua، Golovinomyces biocellatus on Mentha sp.، Golovinomyces montagnei on Silybum marianum، Golovinomyces depressus on Arctium lappa، Golovinomyces orontii on Nicotiana tabacum، Golovinomycescf. orontii on Fraxinus sp.، Golovinomyces sonchicola on Sonchus sp.، Podosphaera aphanis on Agrimonia eupatoria، Podosphaera euphorbiae-hirtae on Pedilianthus sp.، Podosphaera fugax on Geranium dissectum، Podosphaera xanthiis. l. on Dichrocephala sp.، Gerbera sp.، Physalis alkekengi and Vigna unguiculata، Podosphaera pannosa on Rosa sp.، Sawadaea bicornis on Acer sp. Among The identified species Erysiphe australiana and Podosphaera euphorbiae-hirtaeare recorded for the first time from Iran. Moreover، Erysiphe alphitoides on Castanea sativa، Erysiphe betae on Dysphania ambrosioides، Erysiphe heraclei on Petroselinum hortense، Podosphaera xanthiis. lat. on Dichrocephala sp.، Gerbera sp.، Physalis alkekengi and Vigna unguiculata، Golovinomyces ambrosiae on Zinnia sp. and Dahlia sp.، Erysiphe heraclei on Petroselinum hortense، Golovinomyces cf. orontii on Fraxinus sp. are newly reported on these host plants from Iran. In addition، Golovinomyces montagnei، Erysiphe begoniicola and Erysiphe euonymicola are accepted as correct nomenclature for causal agents of powdery mildew on Silybum marianum، Begonia and Euonymus respectively.

Powdery mildew fungi are important obligate parasites of plants. They produce white cover on aerial parts of host plants, which then turn to yellow. The diseased plant becomes yellow and then wilted result in reducing quality as well as quantity of products in field and vegetable crops and also fruit trees. Among all of the control measures against powdery mildew, the most common method is application of the chemical fungicides, after disease incidence. Regarding to the hazards of agrochemicals and also considering the probability of incidence of resistant races of the pathogen, the biological control is considered as a safe and useful method for controlling the disease. The fungi Ampelomyces quisqualis, Pseudozyma flocculosa and Lecanicillium longisporum; the bacterium Bacillus subtilis; the mite Tydeus lambi and twenty-spotted lady beetle Psyllobora vigintimaculata, have been used effectively against the powdery mildew of cucumber, squash, tomato, pepper, grape and rose. Some of these biological agents have been introduced to the market, commercially.

Thirty seven isolates of Erysiphe necator were collected from different vineyards from three regions and nine cities of Khorasan Razavi province within two time periods i. e. May to June and August to September 2009. Their resistance to azoxystrobin + difenconazole (Ortiva®) fungicide as well as cross resistance to penconazole and hexaconazole fungicides registered in Iran for the control of powdery mildew was investigated. A leaf disk bioassay was carried out to determine the resistance of powdery mildew isolates on the basis of EC50 values derived from log-logistic dose-response curves. These subcultures were analyzed for resistance to azoxystrobin + difenconazole. The mean EC50 values of azoxystrobin + difenconazole on E. necator subcultures from vineyards was 0. 279 mg L-1. The highest and the lowest EC50 values were found in Mashhad (0. 622 mg L-1) and Khalilabad (0. 143 mg L-1)، respectively. Frequency distributions were skewed most toward higher resistance to azoxystrobin + difenconazole. The present study demonstrated a steady and significant increase in EC50 values for azoxystrobin + difenconazole during the growing season after multiple applications. Also، there was no cross resistance (P> 0. 05) among fungicides.