Wheat Leaf Blotch Research Articles

Virulence variation and pathotypes of Zymoseptoria tritici isolates causing wheat leaf blotch in Oromia, Ethiopia

Leaf blotch, caused by Zymoseptoria tritici, is a fungal disease that poses a severe threat to wheat production worldwide. Knowledge of virulence variability is crucial in choosing effective control measures. However, there have only been a few studies of the pathogenic variability and pathotypes within Ethiopian isolates. Hence, the objective of this study was to assess the virulence spectrum and variability of Z. tritici isolates. Forty-three isolates were tested for their virulence and pathotype against 7 wheat differential lines that have different resistance genes. A pathogenicity assay detected 41 differential line-specific virulent isolates among 301 interactions between a host and pathogen based on the percentage coverage of the leaf area by pycnidia. Some isolates were virulent against 50 %–60 % of the resistant genes, but most of them were virulent against some differential lines. Isolates such as EtA-11, EtSh-1, EtSh-2, EtSh-4, and EtA-19 expressed broad-spectrum virulence, highlighting that such isolates are useful for germplasm screening. The isolates were classified into 25 pathotypes, defined by their differential virulence responses. They were also assigned to two clusters according to their mean pycnidia percent. Pathotypes and principal component analysis detected 58.1 % and 62.2 % pathogenic diversity in Ethiopian isolates, respectively. The current findings provide information that breeders can use to identify and select more resistant varieties for farmers.

Protective potential of selected microbial and non-microbial biostimulants against Zymoseptoria tritici leaf blotch in winter wheat as affected by the form of N supply.

The production of high-quality food for the growing world population on the one hand and the reduction of chemical-synthetic pesticides on the other hand represents a major challenge for agriculture worldwide. The effectiveness of a combination of microbial and non-microbial biostimulants (BSs) with various nitrogen (N) forms in pathogen defense is discussed as a promising, but still poorly understood bio-based alternative for crop protection. For this reason, nitrate and stabilized ammonium fertilizer both combined with a consortium of Pseudomonas brassicacearum, Bacillus amyloliquefaciens, and Trichoderma harzianum as soil treatment or with a mixture of seaweed extract (Ascophyllum nodosum) together with chitosan-amended micronutrient fertilizer as foliar spray application were compared under controlled greenhouse conditions. Furthermore, a combination of microbial and different non-microbial BSs (seaweed extracts + chitosan) and micronutrients with nitrate or with stabilized ammonium fertilizer was tested under field conditions to improve nutrient availability, promote plant growth, and suppress Zymoseptoria tritici (Zt) in winter wheat. While plant-protective effects against Zt by the microbial consortium application could be observed particularly under ammonium fertilization, the application of seaweed extract-chitosan mixture expressed plant defense against Zt more strongly under nitrate fertilization. In the field trial, the combination of microbial consortium with the seaweed extract-chitosan mixture together with micronutrients zinc (Zn) and manganese (Mn) showed positive effects against Zt under ammonium fertilization, associated with increased levels of defense metabolites. Furthermore, the additional input of Zn and copper (Cu) from the chitosan application improved the micronutrient status by minimizing the risk of Zn and Cu deficiency under controlled and field conditions. The use of BSs and the inoculation of Zt did not show any effects on plant growth and yield neither under controlled greenhouse conditions nor in the field. Summarized, microbial and non-microbial BSs separately applied or even combined together as one treatment did not influence plant growth or yield but made a positive contribution to an N form-dependent promotion of pathogen defense.

Bioactivity of Trichoderma harzianum A peptaibols against Zymoseptoria tritici causal agent of septoria leaf blotch of wheat

Bioactivity of Trichoderma harzianum A peptaibols against Zymoseptoria tritici causal agent of septoria leaf blotch of wheat

Screening of <i>Stb</i> leaf blotch resistance genes of the common wheat varieties

Currently, leaf blotch is one of the main problems in wheat production around the world. The use of DNA markers for screening a large amount of breeding material makes it possible to identify wheat leaf blotch resistance genes quickly and accurately. In this regard, the Federal Agricultural Research Center of the North-East named after N. V. Rudnitsky conducted a search for DNA markers linked to Z. tritici resistance in the genotypes of the collection material of common wheat. There were studied 75 spring and 12 winter bread wheat varieties for the presence of the Stb2, Stb11, Stb12 and Stb13 genes. As a result, Stb leaf blotch resistance genes were found only in 8.0 % of varieties. In the genotype of the spring wheat variety ‘Irmenka 1’, there was determined the presence of three loci of resistance Stb2, Stb11 and Stb13, which were responsible for age-related and juvenile resistance to the disease. The genes of juvenile leaf blotch resistance Stb11 and Stb13 were found in the genotype of the spring common wheat variety ‘Tertsiya’. The Stb2 gene controlling age-related leaf blotch resistance was found in the genotypes of spring wheat varieties ‘Dariya’, ‘Egisar 29’ and ‘Epos’. In the genotypes of winter varieties ‘Gene’ and ‘Ble-seigle’, there were found one gene Stb11 and Stb13, respectively. The Stb12 leaf blotch resistance gene was not identified in the studied wheat varieties. All spring and winter common wheat varieties with Stb-genes can be recommended as sources of leaf blotch resistance in breeding with highly productive varieties adapted to local conditions.

Fungicide sensitivity levels in the Lithuanian Zymoseptoria tritici population in 2021.

Zymoseptoria tritici causes the disease known as septoria leaf blotch in winter wheat and is a major factor in yield loss worldwide. Farmers are inclined to use fungicides to protect their crops; however, the efficacy of these measures is rapidly decreasing due to the natural mechanisms of mutation emergence in pathogen populations. Increasing fungicide resistance is being recorded worldwide, therefore, screening of the current situation in Lithuania is essential to determine the subsequent steps of crop protection strategies. In this study, in vitro fungicide sensitivity tests, mutation detection, and field experiments were carried out. The mean EC50 values for prothioconazole-desthio and mefentrifluconazole were 0.14 and 0.28 mg/l, respectively. Increased frequency of the mutation S524T, linked to DMIs resistance, was observed. Results revealed that the dominant point mutation in the gene CYP51 was I381V, and the most frequent CYP51 haplotype was D13 (V136C, I381V, Y461H, S524T). The mutation G143A, linked to QoI resistance, was detected in ¾ of the population. Mutations conferring resistance to SDHIs were not detected in single pycnidium isolates. Two-year field experiments likewise showed no decline in field efficacy of SDHI fungicide in Lithuania. Moreover, the baseline sensitivity of the Lithuanian Z. tritici population to QiI fungicide fenpicoxamid was established. The findings of this study provide an update on the current status of fungicide resistance in the Lithuanian Z. tritici population.

The Septoria leaf blotch of wheat in Central Kazakhstan: prognosis, evaluation and monitoring with remotely sensed data

Fungal diseases represent a widely spread natural phenomenon affecting many wild and domesticated plants. In nature, all plant species form plant communities of a mixed character, and the spatial pattern of dominant species is usually irregular and spotted. Some species are impregnable to a certain infection, which provides a kind of natural barrier to the infection spreading within the natural community. Under the agricultural environment, when a single plant species may occupy a huge area, the species-specific parasite takes a great advantage to develop focal outbreaks and fast spreading of the infection within the area. The concentration of vulnerable plants and the absence of natural barriers within the agricultural areas provoke outbreaks of fungal diseases that may have highly harmful consequences and result in significant yield losses. One of the purposes of the satellite optical data is an operative, cost-effective diagnostic tool and, in combination with climatic datasets and crop rotation information, a prognosis of fungal disease appearance and severity. This paper describes the system of prognostic and monitoring measures to control the fungal diseases of wheat in Central Kazakhstan, with particular attention to Septoria leaf blotch. The prognostic procedure provides a map of the probability of septoria leaf blotch appearance. The prognosis considers the combination of three main variables: the model of ecological niche for Septoria, the presence of wheat residue, and the vegetation condition index counted for the late spring (May) of the current year. The novel spectral-based approach introduced in this paper is the core component of monitoring activity. The SLBS-equation appears to have high sensitivity to Septoria leaf blotch severity in the middle to late (stages 8–11, accordingly, Feekes growth stages) periods of wheat development. Several other spectral indices (RETA, VSDI, and vegetation indices) may help provide information on the spatial unevenness of wheat crops that may indicate the presence of fungal infection.

A Secondary Metabolite Secreted by Penicillium citrinum Is Able to Enhance Parastagonospora nodorum Sensitivity to Tebuconazole and Azoxystrobin.

Parastagonospora nodorum causes glume and leaf blotch of wheat, a harmful disease resulting in serious losses in grain yield. In many countries including Russia, fungicidal formulations based on triazoles and on triazoles combined with strobilurins are used to control this fungus. However, their prolonged application may promote the selection of fungicide-resistant strains of P. nodorum leading to significant attenuation or even loss of fungicidal effect. Chemosensitization of plant pathogenic fungi with natural compounds represents a promising strategy for mitigating fungicide resistance and other negative impacts of fungicides. In this work, we applied a chemosensitization approach towards P. nodorum strains non-resistant or resistant to tebuconazole or azoxystrobin using 6-demethylmevinolin (6-DMM), a metabolite of Penicillium citrinum. The resistant strains were obtained by the mutagenesis and subsequent culturing on agar media incorporated with increasing doses of Folicur® EC 250 (i.e., tebuconazole) or Quadris® SC 250 (i.e., azoxystrobin). Test strains m8-4 and kd-18, most resistant to tebuconazole and azoxystrobin, respectively, were selected for sensitization experiments. These experiments demonstrated that combining 6-DMM with Folicur® enhanced fungicidal effectiveness in vitro and in vivo in addition to attenuating the resistance of P. nodorum to tebuconazole in vitro. 6-DMM was also found to augment Quadris® efficacy towards kd-18 when applied on detached wheat leaves inoculated with this strain. Experiments on P. nodorum sensitization under greenhouse conditions included preventive (applying test compounds simultaneously with inoculation) or post-inoculation spraying of wheat seedlings with 6-DMM together with Folicur® at dose rates (DR) amounting to 10% and 20% of DR recommended for field application (RDR). Combined treatments were run in parallel with using the same DR of the fungicide and sensitizer, alone. A synergistic effect was observed in both preventive and post-inoculation treatments, when the sensitizer was co-applied with the fungicide at 10% of the RDR. In this case, disease reduction significantly exceeded the protective effect of Folicur® at 10% or 20% of the RDR, alone, and also a calculated additive effect. Collectively, our findings suggest that 6-DMM is promising as a putative component for formulations with triazole and strobilurin fungicides. Such new formulations would improve fungicide efficacy and, potentially, lower rates of fungicides needed for plant pathogen control.

Effects of Crop Rotation on Spring Wheat Yield and Pest Occurrence in Different Tillage Systems: A Multi-Year Experiment in Finnish Growing Conditions

Crop rotation and soil tillage are among key factors impacting cropping system productivity, pest management and soil health. To assess their role in northern cropping systems, we quantified the effects of crop rotation on spring wheat yield in different tillage systems based on a long-term (2005–2017) field experiment in southwestern Finland. In addition, effects of crop rotation on weeds, plant pathogens, and pest insects were assessed. Three types of crop rotation were compared: monoculture (spring wheat), 2-year rotation (spring wheat—turnip rape—spring wheat—barley) and 4-year rotation (spring wheat—turnip rape—barley—pea) under no-tillage and plowing. A diversified crop rotation improved spring wheat yield by up to 30% in no-tillage and by 13% under plowing compared with monoculture. Overall, the yield quantity and quality differences between crop rotations were higher in no-tillage plots than in plowed plots. The occurrence of weed species in spring wheat before herbicide control was highest in the four-year crop rotation and lowest in the wheat monoculture. For plant diseases, wheat leaf blotch disease severity, mainly caused by Pyrenophora tritici-repentis, was lowest in the most diverse crop rotation. On average, wheat leaf blotch disease severity was 20% less when wheat was grown every fourth year compared with wheat monoculture. The effect of crop rotation on stem and root diseases became apparent after 6 years of rotation and the disease index was lowest in the most diverse crop rotation. Neither rotation nor tillage affected the control need of wheat midge (Sitodiplosis mosellana). Based on our results, diverse crop rotations including cereals, oilseed crops, and legumes increase yield and reduce plant disease severity of spring wheat in Finland, with the magnitude being larger in no-tillage systems.

The septoria leaf blotch of wheat in Central Kazakhstan: prognosis, evaluation and monitoring with remotely sensed data

Fungal diseases represent a widely spread natural phenomenon affecting many of wild and domesticated plants. In nature, all plant species forms plant communities of a mixed character, and the spatial pattern of dominant species is usually irregular and spotted. Some species are impregnable to a certain infection, which provides a kind of natural barrier to the infection spread within the natural community. Under the agricultural environment, when the single plant species may occupy a huge area, the species-specific parasite takes a great advantage to develop focal outbreaks and fast spreading of the infection within the area. The concentration of vulnerable plants and the absence of natural barriers within the agricultural areas provokes outbreaks of fungal diseases, that may have highly harmful consequences and result in significant yield losses. One of the purposes of the satellite optical data is an operative, cost-effective diagnostic and, in combination with climatic datasets and crop rotation information, a prognosis of fungal disease appearance and severity. In this paper, we describe the system of prognostic and monitoring measures to control the fungal diseases of wheat in Central Kazakhstan with special attention to septoria leaf blotch. The prognostic procedure provides a map of the probability of septoria leaf blotch appearance. The prognosis takes into consideration the combination of three main variables: the model of ecological niche for Septoria, the presence of wheat residue, and Vegetation Condition Index counted for the late spring (May) of the current year. The new spectral index, introduced in this paper, is the core component of monitoring activity. The index is sensitive to septoria leaf blotch severity at middle to late (stages 8-11, accordingly Feekes growth stages) periods of wheat development. Several other indices (RETA, VSDI, vegetation indices) may be of help in providing information on the spatial unevenness of wheat crops that may indicate the presence of fungal infection.

Florylpicoxamid, a new picolinamide fungicide with broad spectrum activity.

Following the introduction of fenpicoxamid, a natural product-based fungicide targeting the Qi site of mitochondrial cytochrome bc1 complex, a second generation fully synthetic picolinamide, florylpicoxamid, was discovered and its biological activity and attributes were characterized. In vitro fungal growth inhibition assays and in planta glasshouse biological activity evaluations showed florylpicoxamid was active against 21 different plant pathogenic fungi within the phyla Ascomycota and Basidiomycota. Among the pathogens evaluated, florylpicoxamid was most potent against Zymoseptoria tritici, the causal organism of wheat leaf blotch, providing 80% growth inhibition in vitro at 0.0046 mg L-1 and 80% disease control in planta at 0.03 mg L-1 when applied as a preventative treatment. Florylpicoxamid was more efficacious than epoxiconazole, fluxapyroxad, and benzovindiflupyr versus a Z. tritici wild-type isolate when applied as curative and preventative treatments, with superior 10-day curative reachback activity. Analytical studies and in planta tests demonstrated that florylpicoxamid partitioned into plants quickly and showed good systemicity and translaminar activity on both monocot and dicot plants. No cross-resistance was observed between florylpicoxamid and strobilurin or azole fungicides. Florylpicoxamid exerts its preventative effect by preventing spore germination on the leaf surface and curative activity by arresting mycelial growth and pycnidia development in leaf tissue. With strong broad spectrum fungicidal activity, florylpicoxamid delivers an innovative solution for growers to sustain high productivity and quality of many crops, and also provides a new option for developing effective strategies for fungicide resistance management. © 2021 Society of Chemical Industry.

Hidden in plain sight: a molecular field survey of three wheat leaf blotch fungal diseases in North-Western Europe shows co-infection is widespread

Wheat (Triticum aestivum L.) yields are commonly affected by foliar infection by fungal pathogens. Of these, three wheat leaf blotch fungal diseases, septoria nodorum blotch (SNB), tan spot (TS) and septoria tritici blotch (STB), caused by Parastagonospora nodorum (Pn), Pyrenophora tritici-repentis (Ptr) and Zymoseptoria tritici (Zt), respectively, induce major yield losses. Infection results in necrotic areas on the leaf, and it is often difficult to determine the underlying causative pathogen from visible symptoms alone, especially in mixed infections. Here, a regional survey of 330 wheat samples collected across three seasons (years 2015–2017) from four north-west European countries was undertaken. Using quantitative polymerase chain reaction (qPCR) assays specific for each pathogen, as well as disease assessment of leaf materials, distinct regional differences were identified. Two-thirds (65%) of all samples harbored at least two of the three pathogens. Norway had high SNB abundance, but also showed mixed infections of SNB, TS and STB. In Germany, TS was prevalent, with STB also common. Danish samples commonly possessed all three pathogens, with STB prevalent, followed by TS and SNB. The UK had a major prevalence of STB with minimal occurrence of TS and SNB. Across all samples, qPCR identified Zt, Pn and Ptr in 90%, 54% and 57% of samples, respectively. For each pathogen, average disease levels via visual assessment showed modest positive correlation with fungal DNA concentrations (R2 = 0.13–0.32). Overall, our study highlights that the occurrence of mixed infection is common and widespread, with important implications for wheat disease management and breeding strategies.

Investigation of the expression pattern of Ribonuclease, Cysteine protease, and Glutathione peroxidase genes in response to septoria leaf blotch in bread wheat

One of the most important diseases of wheat is septoria leaf blotch caused by Zymoseptoria tritici. Pathogen-related proteins cause disease resistance in plants. To identify the onset time of wheat defence response against the pathogen, two wheat cultivars of susceptible (Tajan) and resistant (Nogal), were inoculated with spores of Z. tritici in the two-leaf stage. Sampling was performed and expression pattern of Ribonuclease, Cysteineprotease and Glutathione peroxidase-1 genes were analyzed by Real-Time PCR method. The results showed that these genes are good candidates for wheat defense and their expression patterns were different in both susceptible and resistant cultivars.

Large-scale study validates that regional fungicide applications are major determinants of resistance evolution in the wheat pathogen Zymoseptoria tritici in France.

In modern cropping systems, the near-universal use of plant protection products selects for resistance in pest populations. The emergence and evolution of this adaptive trait threaten treatment efficacy. We identified determinants of fungicide resistance evolution and quantified their effects at a large spatiotemporal scale. We focused on Zymoseptoria tritici, which causes leaf blotch in wheat. Phenotypes of qualitative or quantitative resistance to various fungicides were monitored annually, from 2004 to 2017, at about 70 sites throughout 22 regions of France (territorial units of 25000km2 on average). We modelled changes in resistance frequency with regional anti-Septoria fungicide use, yield losses due to the disease and the regional area under organic wheat. The major driver of resistance dynamics was fungicide use at the regional scale. We estimated its effect on the increase in resistance and relative apparent fitness of each resistance phenotype. The predictions of the model replicated the spatiotemporal patterns of resistance observed in field populations (R2 from 0.56 to 0.82). The evolution of fungicide resistance is mainly determined at the regional scale. This study therefore showed that collective management at the regional scale could effectively complete local actions.

Study of the species composition and population structure of winter wheat leaf blotch pathogens in the central chernozem region of the Russian Federation

For the period of 2020, the species composition of winter wheat leaf blotch pathogens on the territory of the Central Chernozem region was studied. It is shown that the Zymoseptoria tritici species dominates in the pathogenic complex during all phases of wheat vegetation. Under the conditions of the year, the other two species - the pathogen of the disease: Parastagonospora nodorum and Parastagonospora avenae f. sp. triticea had no economic significance. The populations of the species Zymoseptoria tritici, formed on winter and spring wheat cultivats according to morphological, physiological and pathogenic properties, were studied. It is shown that black corrugated colonies with an average growth rate and high sporulation predominate. Using monogenic lines, virulence phenotypes were determined in isolates taken from infectious wheat material. Seven virulence phenotypes were identified. All isolates hit the test lines from 2 to 4 points, therefore they were characterized by wide virulence and high aggressiveness. The information obtained is necessary for the development of a methodology for resistance breeding.

Biological Rationale for the Protein Growth Stimulant Application to Increase Wheat Yield and Assessment of Grain Quality Using Microfocus X-ray and Optical Imaging Techniques

A new plant growth stimulant was developed according to the technology engineered by the scientists of ITMO and SPBGAU Universities. The biological effectiveness of the preparation was assessed by measuring 20 wheat productivity parameters and 16 parameters of various types of pathogenesis formed during the progress of root rot caused by Helminthosporium, different types of rust, powdery mildew, and wheat leaf blotch. Application of the stimulant promoted a potential yield increase in 64% of samples (statistically significant at P < 0.05 in 28% of samples). Among the essential parameters of the yield formula, the preparation exerted the most remarkable action on spike length, the number of spikelets per spike, number of grains per spike, and weight of grains in one spike. Foliar spraying of plants with the protein growth stimulant promoted an increase in total nitrogen content of wheat leaves by an average of 84.6% in 92% of samples. Wheat grains exhibited better characteristics with the application of the protein stimulant compared to the control according to the results of microfocus X-ray radiography and optical analysis. The use of the protein growth stimulant delayed the progress rate of Helminthosporium root rot by an average of 60%, powdery mildew by 5% (based on the number of spots and their area by 36 and 52%, respectively), brown rust by 2.9% (based on the number of pustules per leaf by 76.8% and pustule area by 79.7%), and wheat leaf blotch by 15.9% compared with the control. The stimulant effectiveness has been found to depend strongly on wheat variety. Thus, the prospects of using the new, effective plant-growth stimulant to increase wheat productivity and protect against diseases have been shown experimentally. Further research is necessary due to the heterogeneity of outcomes in experiment variations.

Contribution of Parastagonospora nodorum to the leaf and glume blotch of durum wheat in Bulgaria

Abstract. Parastagonospora nodorum is an important necrotrophic fungal pathogen causing leaf and glume blotch of wheat worldwide. The disease can result in significant losses in grain yield and quality. The purpose of the current investigation was to estimate the occurrence of P. nodorum as a foliar and ear pathogen of durum wheat and disease severity on a set of cultivars under natural infection. Field experiments were performed at two locations (Sofia and Chirpan) in the period 2010-2017. Twelve winter cultivars of durum wheat were involved in the study. P. nodorum was not found at both locations in 2010 and 2011. Thereafter the pathogen was recorded on the leaves of durum wheat in Sofia every year except 2013. Symptoms included chlorosis and necrosis of the leaf tissue. The strongest manifestation of the disease was observed in 2016 and especially in 2017. In Chirpan leaf blotch was noticed only in 2 out of 8 growing seasons. The ear infection led to development of dark brown patches on the glumes, which later became purple-brown. These symptoms were noted in Sofia in 2014, 2016 and 2017. In Chirpan, glume blotch of studied cultivars was recorded in 2017 but in the previous year the symptoms were widely observed on some genotypes among the initial breeding material of durum wheat. In the present investigation P. nodorum caused leaf and glume blotch only. Symptoms on stems, nodes and leaf sheaths were not noted at both locations. The 12 cultivars under study differed in their susceptibility to leaf and glume blotch. The leaf symptoms caused by P. nodorum were recorded on all cultivars, but were more pronounced on Zvezditsa, Deyana and GK Bétadur. The glume blotch was more noticeable on Vazhod. The results of this multiyear research showed that although P. nodorum did not appear every year, the pathogen could contribute to the leaf and glume blotch of durum wheat under conditions favourable for disease development. The evaluation of cultivars demonstrated encouraging preliminary results. Several cultivars showed lower disease severity on flag leaf and no or little infection on the ear. They deserve further studies on resistance to P. nodorum.

Assessment of yield losses caused by Stagonospora leaf and glume blotch (SLGB) of wheat; its status and distribution in Himachal Pradesh

Stagonospora leaf and glume blotch (SLGB) of wheat caused by Parastagonospora nodorum is one of the emerging diseases in Himachal Pradesh. In the present study, survey was conducted in major wheat growing areas and the severity on earheads was observed during 2013–2014, 2014–2015 and 2015–2016 cropping seasons. Out of seven districts surveyed, Kangra, Kullu and Mandi faced higher severity of SLGB and based on survey data, Malan was considered as the disease hot spot. Disease severity was considerably higher during 2014–2015 (45.0%) than 2013–2014 (30.0%) and 2015–2016 (13.0%) respectively due to congenial climatic conditions i.e. lower temperatures (14.10–17.74 °C), higher humidity (50.81–55.79%) and rainfall (35.85–154.95mm) and more number of rainy days (3.7–6.2). The sites located in valley areas, near water bodies and rivers recorded higher disease severity due to favourable microclimate. The yield losses estimated in susceptible variety HPW 249 were 12.4 and 14.7% during 2013–2014 and 2014–2015 respectively. Two sprays of propiconazole (0.1%) at 15 days interval were quite effective giving 89.6 and 85.9% control of the disease during 2013–2014 and 2014–2015 correspondingly.

Co-application of Difenoconazole with Thymol Results in Suppression of a Parastagonospora Nodorum Mutant Strain Resistant to this Triazole

Results of in vitro study of thymol, a natural chemosensitizer, as a potential agent for overcoming of difenoconazole resistance of Parastagonospora nodorum causing glume and leaf blotch of wheat are first reported. The level of difenoconazole resistance of a natural mutant PNm1 strain with low sensitivity to the Dividend fungicide (a.i. difenoconazole) was determined by the cultivation of this isolate on potato dextrose agar in the presence of the fungicide at sub-lethal and lethal (in relation to the initial fungicide-sensitive strain) concentrations. A principal possibility of the thymol use to overcome resistance of P. nodorum to DMI (demethylation inhibitors) fungicides is shown. Co-application of this compound with Dividend SC, 3 % resulted in a significant reduction of resistance of the mutant strain and enhancement of its sensitivity to difenoconazole up to the level corresponding to the initial non-resistant isolate.

Application of PCR based diagnostics in the exploration of Parastagonospora nodorum prevalence in wheat growing regions of Himachal Pradesh

Stagonospora leaf and glume blotch (SLGB) of wheat caused by Parastagonospora nodorum (formerly Stagonospora nodorum) has recently emerged as a major problem in changing climatic conditions of Himachal Pradesh (HP), especially during delayed winter rains. In the present studies symptomatology, morpho-cultural as well as molecular marker based identification showed the prevalence of disease in the state and conclusively proved that leaf and glume blotch of wheat is caused by P. nodorum. The test pathogen showed 100% homology with other reported P. nodorum isolates by rDNA (ribosomal DNA) analysis. In addition, the amplification of rDNA region of 36 P. nodorum isolates representing various agro-ecological areas of HP and one infected wheat leaf sample generated an amplicon of ~ 449-bp with JB433 (5′-ACACTCAGTAGTTTACTACT-3′) and JB434 (5′-TGTGCTGCGCTTCAATA-3′) P. nodorum specific primer pair whereas no amplification was observed with the genomic DNA of Septoria titici, Stemphylium vesicarium and healthy wheat leaf sample. This study on integration of morpho-cultural and microscopic methods along with PCR based technique could form basis for routine diagnosis of the SLGB in wheat samples during early growth stages of crop in the seed production fields.

Determining and modelling the effective period of fungicides against septoria leaf blotch in winter wheat

The aim of this work was to develop a model to predict the effective period of fungicides for control of Zymoseptoria tritici (septoria leaf blotch) in winter wheat. Efficacy and duration of fungicidal effects of three fungicides, namely Bravo 500 (chlorothalonil), Epoxion (epoxiconazole), Imbrex (fluxapyroxad) and a mixture of Epoxion + Imbrex, were examined under field and laboratory conditions. In order to design a simulation model, a method for calculating the effective period of fungicides was developed. Key feature of this method is the comparison of disease progress curves on treated and untreated plants, based on data recorded in field trials. The effective period was considered to end when, after a prior fungicide application, rates of disease progress on treated and untreated plants became equal again. The effective periods of fungicides were calculated by subtracting latency periods of Z. tritici from the time point of recovery of maximum disease progress and lay between 16 and 22 days, depending on the fungicide. These findings were confirmed by fungicide residue analyses at the calculated time of expired fungicide efficacy where 3–44% of the initially applied doses of active substance were detectable. Based on calculations from field trials, a model to predict the fungicide effective periods was developed for field-grown winter wheat. Air temperature, precipitation and, depending on the fungicide, relative humidity were identified to be significant determinants of fungicide efficacy and effective periods. The validation confirmed the reliable prediction of the effective period of fungicides and a corresponding model named OPTIFUNG was developed. OPTIFUNG will be integrated in the wheat disease decision support model SEPTRI in order to optimize the timing and frequency of fungicide applications against septoria leaf blotch by including fungicide effective periods. As the method is based on general epidemiological principles, it may be useful for and is adaptable to yet any other leaf diseases in cereals which require sequential sprays with fungicides.