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Basal stem rot (BSR), caused by Sclerotinia sclerotiorum and Sclerotinia minor, is one of the most devastating diseases of sunflower worldwide. The use of resistant cultivars is the most economical strategy to manage BSR. However, development of cultivars with effective resistance requires adequate information on the interactions of host genotypes with pathogen isolates. To this aim, the present study was conducted to assess the reactions of 100 oilseed sunflower genotypes of diverse origin to three isolates of each of S. sclerotiorum and S. minor at the seedling stage in growth room conditions. Sunflower genotypes exhibited isolate-specific resistance (differential interactions) to both Sclerotinia species. Among interactions (n = 600), 24 isolate-specific resistances were found to S. sclerotiorum and six to S. minor in 24 genotypes. None of the genotypes was resistant to all fungal isolates. Among the resistant genotypes, “H543R/H543R” and “110” were resistant to two isolates of S. sclerotiorum, whereas others were resistant to one isolate of each of the pathogens. Furthermore, 21 genotypes were specifically resistant to only isolates of S. sclerotiorum or only isolates of S. minor, while, “8A*/LC1064C,” “H156A/H543R,” and “110” showed resistance to one or two isolates of both fungal species. Comparison of mean disease severity scores revealed that sunflower genotype “110” had the greatest general resistance to S. sclerotiorum and genotype “ENSAT 699” to S. minor. Cluster analysis effectively identified the existence of genetic variability among sunflower genotypes and classified them into three or four separate classes based on disease severity scores after infection by S. sclerotiorum and S. minor, respectively. The expression level of pathogenesis-related 5 (PR5) protein was investigated in a resistant (8A*/LC1064C) and a susceptible genotype (SDR19) inoculated with S. sclerotiorum isolates. Mean comparison revealed that the expression of PR5 in 8A*/LC1064C was fivefold higher than SDR19 at 3 h after inoculation indicating the possible involvement of this protein in resistance. The resistance sources identified in the present study have the potential for use in breeding programs to develop sunflower hybrids with BSR resistance.

Phytopythium is a globally distributed genus, species of which occur in various ecological niches. Despite their importance as plant pathogens, information on species diversity and their distributi...

In this study, sensitivities of 156 Sclerotinia sclerotiorum isolates collected from sunflower fields of West Azarbaijan province, Iran, were assessed to carbendazim and iprodione, and the baseline sensitivities were established for azoxystrobin and tebuconazole. Resistance to carbendazim and iprodione was observed in 53.85% and 4.49% of the isolates, respectively. The 50% effective concentration (EC₅₀) values of azoxystrobin for the isolates ranged from 0.017 to 3.515 μg/ml with a mean of 0.330 μg/ml, and 8.97% of the strains showed low levels of resistance to the fungicide. However, in the presence of salicylhydroxamic acid, all isolates were sensitive to azoxystrobin and EC₅₀ values ranged from 0.015 to 0.263 μg/ml with a mean of 0.086 μg/ml. All isolates were found to be sensitive to tebuconazole, and EC₅₀ values ranged from 0.003 to 0.177 μg/ml with a mean of 0.036 μg/ml. Among the multiple‐resistant isolates, the strains exhibiting resistance to both carbendazim and iprodione were detected in the highest frequency (4.49%). No correlation was observed between mycelial growth and aggressiveness with fungicide sensitivity of the isolates suggesting the absence of fitness cost associated with resistance to the studied fungicides. The results indicated that iprodione, azoxystrobin and tebuconazole could be effectively used in rotation or mixture in spray programmes to manage S. sclerotiorum in the region. The baselines established for azoxystrobin and tebuconazole would be useful in monitoring the fungal populations in the province to assess possible shifts in fungicide sensitivity of S. sclerotiorum isolates in the future.

Sclerotinia sclerotiorum is one of the most destructive fungal pathogens infecting a wide array of plant species worldwide. Management of this pathogen relies on the coordinated use of fungicides and resistant host cultivars with other control measures, but the effectiveness of these methods requires knowledge of the genetic variability and structure of the fungal populations. To provide insight into the genetic diversity and structure of this pathogen in West Azarbaijan province of Iran, a total of 136 isolates were collected from symptomatic sunflower and cabbage plants within fields in three regions and analysed using inter-simple sequence repeat (ISSR) markers and intergenic spacer (IGS) region of the rRNA gene sequences. A total of 83 ISSR multilocus genotypes (MLGs) were identified, some of which were shared among at least two regional or host populations but in a low frequency. High genotypic diversity, low levels of clonal fraction, and random association of ISSR loci in a region indicated a low level of clonal reproduction, and possibly a high level of sexually recombining life cycle for the pathogen in the province. Marker analyses revealed that the pathogen was spatially homogeneous among fields, and thus similar control measures, such as the choice of resistant cultivars and fungicides, may effectively manage S. sclerotiorum within the region. Four IGS haplotypes (IGS1–IGS4) were detected within populations with IGS3 being the most prevalent haplotype. The low IGS haplotype diversity, the absence of spatial structure, and shared MLGs among populations may suggest a single introduction and subsequent dispersal of S. sclerotiorum within West Azarbaijan province.

Two new species of Pythium Pringsheim isolated from soils of northwestern regions in Iran, are described: P. monoclinum Abrinbana, Abdollahz. & Badali, sp. nov., and P. iranense, sp. nov. Both species are morphologically distinct from all known species. Pythium monoclinum Abrinbana, Abdollahz. & Badali, sp. nov., is morphologically characterized by the presence of a swollen element in oogonial stalks below terminal oogonia, mostly monoclinous antheridia originating at various distances from the oogonia that occasionally arising from inflated part of oogonial stalk and, rarely production of peanut-shaped and double oospores. Pythium iranense, sp. nov., is distinguished from other species of the genus by the production of smooth-walled oogonia that occasionally have 1-3 papillae, globose to rarely elongated oogonia, 1-2(-5) antheridia per oogonium or crowd of antheridia around oogonia, 1-2 rarely 3-4 oospores per oogonium, rarely peanut-shaped oospores and immature oospores provided with 1-6 projections. Phylogenetic relationships of the isolates belonging to these new species with other related species were investigated using internal transcribed spacers of rRNA genes and partial cytochrome c oxidase subunit I sequence data. The phylogenetic analyses separated the two species from closely related species and placed P. iranense, sp. nov., in clade J1 but the clade of P. monoclinum Abrinbana, Abdollahz. & Badali, sp. nov., was unknown.

Basal stem rot (BSR), caused by Sclerotinia sclerotiorum and S. minor, is one of the most important fungal diseases of sunflower (Helianthus annuus L.) causing significant yield losses worldwide. Using resistant cultivars is the most effective method to manage BSR in the field. Therefore, identification of resistant genotypes and genomic regions related to the disease resistance is necessary for employment in the field and for development of resistant cultivars. In this study, the reaction of 100 oilseed sunflower lines was investigated against three isolates from each of the S. sclerotiorum and S. minor species in controlled conditions and association analysis of resistance traits was performed using retrotransposon-based DNA markers. The sunflower germplasm exhibited various reactions against the fungal isolates as the mean necrosis percentage in basal stem of the lines ranged from 30.67 to 100. The genotypes H156A/H543R, 110 and 8A×/LC1064C were resistant to the isolates of both species. Population structure analysis subdivided the genotypes into two subpopulations. Association analysis using general and mixed linear models identified 15 and 14 loci, respectively, which were significantly (P ≤ 0.01) associated with resistant traits. Phenotypic variance explained by QTLs (R2) ranged from 1 to 23%. The markers UF1, LTR1064-A13, LTR1061-UBC818 and LTR1064–65 were commonly associated with the traits conferring resistance to more than one fungal isolate. This was the first study on QTL mapping of genomic regions responsible for resistance to S. sclerotiorum and S. minor using retrotransposon-based DNA markers in and provided an evidence for effectiveness of these markers in association analysis of sunflower. The QTLs and the markers associated with the resistance traits can be useful in marker-aided programs to develop sunflower cultivars with effective resistance to BSR caused by the two Sclerotinia species.

Septoria tritici blotch (STB), caused by Zymoseptoria tritici has been considered one of the important diseases of wheat in Europe and elsewhere including Iran. The most economical strategy to control the disease is the use of genetic resistance. To this aim, this study was conducted to identify new sources of resistance to STB and to investigate the effectiveness of known Stb genes against six Iranian isolates of Z. tritici. Genetic variability analysis using random amplified polymorphic DNA (RAPD) markers revealed high polymorphic banding patterns indicating that a high genetic variability existed among the isolates. Inoculation assays identified 116 isolate-specific resistances among all interactions (n = 420). Of 52 genotypes, 26 wheat genotypes showed no isolate-specific responses and were susceptible to all isolates, which may explain increasing epidemics of Z. tritici occurring in major wheat-growing regions in Iran. Five genotypes were highly resistant to all isolates. Effectiveness determination of Stb genes revealed that Iranian isolates have a broad virulence spectrum against most of the known Stb genes. Among all Stb genes, Stb15 and Stb16/Stb17 in cultivars Arina, Riband and M3 were the most effective resistance genes and conferred resistance to all isolates tested. Hence, these genes should be effective in breeding programs in Iran to control the disease.

Three new species of Pythium: P. ershadii, P. pyrioosporum, and P. urmianum from soils of various regions in Iran are described and illustrated. These species are morphologically distinct from all other known species. Pythium ershadii is morphologically characterized by pyriform ornamented oogonia and rarely production of pyriform oospores. Pythium pyrioosporum differs from other species of the genus by the production of pyriform oospores and smooth walled oogonia, oospores with a tapering elongation toward a hypogynous antheridium and intercalary hypogynous antheridia. Pythium urmianum is distinguished by the presence of intercalary hypogynous antheridia, smooth walled oogonia formed laterally on hyphae or on short side branches and peanut-shaped oospores. Phylogenetic relationships of these new taxa with other Pythium species were investigated using internal transcribed spacers rDNA and partial coxI sequence data. The three species reside in clade E1 and are separated from closely related species.

Septoria tritici blotch (STB), caused by Mycosphaerella graminicola has recently become one of the devastating diseases in Iran causing significant yield losses on most commercial bread and durum wheat cultivars. Iran is located in the Fertile Crescent, a region where wheat was historically domesticated; and, thus, landraces derived from this region are of considerable global interest for identification of new sources of resistance to various stresses. Here, we report on the resistance responses of 45 tetraploid wheat landraces collected from different provinces of Iran to eight M. graminicola isolates. In total 138 isolate-specific resistances were found among all interactions (n = 360). The highest number of specific resistances (30 out of 32 interactions) was found in wheat landraces collected from West Azarbaijan. In contrast, all landraces from Kordestan were highly susceptible to M. graminicola isolates and only one isolate-specific resistance was identified among 106 isolate-wheat interactions. Kermanshah landraces showed the highest resistance variation against different isolates. About 57 isolate-specific resistances were identified among 104 interactions. Ilam landraces were highly resistant to STB as 28 specific resistances were observed among 32 interactions. Markazi (n = 2) and Sistan-Baluchestan (n = 1) were susceptible to all isolates tested. Landraces from Lorestan were generally susceptible to isolates tested as 26 susceptible responses were observed out of 32 interactions. Our results indicate that landraces collected from the Fertile Crescent region may possess diverse effective resistance genes or valuable broad spectrum resistance genes, and that their identification is of interest and can be exploited in breeding programs.

Co-evolution of wheat and its devastating pathogen Mycosphaerella graminicola (anamorph Septoria tritici), the causal agent of septoria tritici blotch, a foliar disease of wheat, is suggested to occur in Fertile Crescent as their center of origin and, thus, interaction between pathogen virulence and host resistance is important subject to be addressed. We have investigated resistance spectra of 54 wheat genotypes including a set of differentials carrying known resistance genes and virulence patterns of 14 M. graminicola isolates at seedling stage under controlled environmental conditions. The isolates were collected in Iran from five provinces. Diversity in virulence and aggressiveness was observed among the isolates from four provinces. Isolates collected from Golestan province were virulent to all wheat genotypes from germplasm of Iran, while specific resistances were identified to the isolates from other provinces. Among wheat genotypes, cvs. Chamran, Morvarid and Hirmand had the greatest number of specific resistances as well as partial resistance. Wheat genotypes of the differential set also differed in their reactions to the isolates. Arina, Flame and TE 9111 were specifically resistant to the greatest number of isolates from different provinces. Most isolates were virulent to the other differentials such as cvs. Shafir, Estanzuela federal and Courtot indicating that extensive adaption of virulence to most of the known resistance genes (Stb) has occurred in these regions. The new sources of resistance to highly virulent isolates from Iran may also be utilized in wheat breeding programs to develop resistant cultivars against pathogen populations in other countries.

To provide insight into the genetic structure of Mycosphaerella graminicola populations in Iran, a total of 221 isolates were collected from naturally infected wheat fields of five major wheat-growing provinces and analysed using AFLP markers and mating-type loci. All populations showed intermediate to high genotypic diversity. In the Golestan and Ardabil populations two mating types were found at near-equal frequencies, whilst all populations were in gametic disequilibrium. Moreover, clonal haplotypes were identified in different sampling sites within a field in both the Khuzestan and Fars provinces, demonstrating that pycnidia are probably the primary source of inoculum. All five populations had low levels of gene diversity and had private bands. Low levels of gene flow and high genetic differentiation were observed among populations and different clustering methods revealed five genetically distinct groups in accordance with the sampling areas. The Golestan and East Azarbaijan populations were more genetically differentiated than the others. Random genetic drift, selection and geographic barriers may account for the differentiation of the populations. The results of this study indicate a population structure of M. graminicola in Iran contrasting to that of most other countries studied.

The cyclic AMP (cAMP) signaling and mitogen-activated protein (MAP) kinase pathways are the most important signal transduction pathways in eukaryotes. In many plant pathogenic fungi they play pivotal roles in virulence and development. Identification and understanding the role of signal transduction pathways in regulation of cellular responses require robust biochemical techniques. Determination of both the phosphorylation status of MAPKs and the intracellular levels of cAMP is required to unravel the function of these pathways during adaptation of fungi to environmental stress conditions or when particular fungal genes are disrupted or silenced. Here we describe protocols to determine the phosphorylation status of three different MAPKs including Fus3, Slt2 and Hog1 as well as a protocol to measure the intracellular levels of cAMP levels. These protocols can be adapted for a wide range of fungi.

The cyclic AMP (cAMP) signaling and mitogen-activated protein (MAP) kinase pathways are the most important signal transduction pathways in eukaryotes. In many plant pathogenic fungi they play pivotal roles in virulence and development. Identifi cation and understanding the role of signal transduction pathways in regulation of cellular responses require robust biochemical techniques. Determination of both the phosphorylation status of MAPKs and the intracellular levels of cAMP is required to unravel the function of these pathways during adaptation of fungi to environmental stress conditions or when particular fungal genes are disrupted or silenced. Here we describe protocols to determine the phosphorylation status of three different MAPKs including Fus3, Slt2 and Hog1 as well as a protocol to measure the intracellular levels of cAMP levels. These protocols can be adapted for a wide range of fungi