Sensitivity of Mycosphaerella graminicola (anamorph: Septoria tritici) to DMI fungicides across Europe and impact on field performance

Since the occurrence and spread of resistance to quinone outside inhibitors (QoI) in Mycosphaerella graminicola in the early 2000s in Europe, demethylation inhibitors (DMIs) form the backbone for control of Septoria leaf blotch. European monitoring studies, carried out by various research institutes and DMI manufacturers, have shown a shift of the European M. graminicola population towards increased ED₅₀ values for DMI fungicides. Populations of M. graminicola consist of very heterogeneous isolates within a region, and even within a field, in terms of DMI sensitivity. Sensitivity to DMIs is influenced by the haplotype of CYP51, the target of DMIs. New CYP51‐haplotypes have emerged and the frequency of less sensitive haplotypes in Europe has increased in recent years. Studies with efflux transporter inhibitors showed that not only CYP51, but also enhanced efflux, may play a role in the DMI sensitivity response. Sensitivity studies with 5 DMIs registered for Septoria leaf blotch control indicated that sensitivity of isolates to the 5 DMIs is heterogeneous and the overall correlation of sensitivity to the different DMIs is poor. A key requirement for sustainable control and resistance management of Septoria leaf blotch is therefore the continued availability of different DMIs.     

Resistance of wheat pathogen Zymoseptoria tritici to DMI and QoI fungicides in the Nordic-Baltic region - a status

Septoria tritici blotch (STB) caused by the ascomycete Zymoseptoria tritici (Z. tritici) is currently the most prevalent foliar disease in wheat in the Nordic-Baltic region. Fungicide availability in this region differs greatly and is generally more limited than in other European regions. Monitoring of fungicide sensitivity is an essential tool to survey changes in fungal populations in order to react and be able to adapt recommendations for fungicide use. In this study the authors give an overview of the current situation of 14α-demethylation inhibitor (DMI) and quinone outside inhibitor (QoI) sensitivity of Z. tritici from Scandinavia and the Baltic countries. A total of 985 isolates from the Nordic-Baltic region were investigated for EC₅₀ of DMI epoxiconazole and prothioconazole. Fungicide sensitivity remains at a high level with values ranging from 0.07 to 0.48 mg L^?1 for epoxiconazole and 1.17 to 9.47 mg L^?1 for prothioconazole. Point mutation I381V in the DMI target gene CYP51 was dominant throughout the region, but mutations D134G, V136A/C and S524T were also detected in the population in 2014. Screening for inserts in the CYP51 promoter region revealed that a ~ 1000 bp insert is predominant in the entire region. Only a single isolate was found in Denmark, harbouring the 120 bp insert, known to reduce fungicide sensitivity. Two Danish isolates which had elevated resistance levels were associated with an enhanced efflux. Significant differences were found across the area for the presence of G143A, conferring QoI resistance. As there is only limited access to results from this area, these findings can serve as reference for future fungicide sensitivity investigations and for evaluation of changes in the Northern European Z. tritici population.     

Mutations in the CYP51 gene correlated with changes in sensitivity to sterol 14 alpha-demethylation inhibitors in field isolates of Mycosphaerella graminicola

In France, as in many other European countries, Mycosphaerella graminicola (Fuckel) Schr?ter in Cohn (anamorph Septoria tritici), the causal agent of wheat leaf blotch, is controlled by foliar applications of fungicides. With the recent generalization of resistance to strobilurins (QoIs), reliable control is mainly dependent upon inhibitors of sterol 14 alpha-demethylation (DMIs). To date, strains with reduced sensitivity to DMIs are widespread, but disease control using members of this class of sterol biosynthesis inhibitors has not been compromised. In this study, sensitivity assays based on in vitro effects of fungicides towards germ-tube elongation allowed the characterization of seven DMI-resistant phenotypes. In four of them, cross-resistance was not observed between all tested DMIs; this characteristic concerned prochloraz, triflumizole, fluquinconazole and tebuconazole. Moreover, the highest resistant factors to most DMIs were found only in recent isolates; according to their response towards prochloraz, they were classified into two categories. Molecular studies showed that DMI resistance was associated with mutations in the CYP51 gene encoding the sterol 14 alpha-demethylase. Alterations at codons 459, 460 and 461 were related to low resistance levels, whereas, at position 381, a valine instead of an isoleucine, in combination with the previous changes, determined the highest resistance levels to all DMIs except prochloraz. Mutations in codons 316 and 317 were also found in some isolates exhibiting low resistance factors towards most DMIs.     

Assessment of fungicide resistance and pathogen diversity in Erysiphe necator using quantitative real-time PCR assays

BACKGROUND: Management of grapevine powdery mildew Erysiphe necator Schw. requires fungicide treatments such as sterol demethylation inhibitors (DMIs) or mitochondrial inhibitors (QoIs). Recently, reduction in the efficacy of DMIs or QoIs was reported in Europe and the United States. The aim of the present study was to develop real‐time qPCR tools to detect and quantify several CYP51 gene variants of E. necator: (i) A versus B groups (G37A) and (ii) sensitive versus resistant to sterol demethylase inhibitor fungicides (Y136F). RESULTS: The efficacy of the qPCR tools developed was better than the CAPS method, with a limit of 2 pg for E necator DNA, 0.06 ng for genetic group A and 1.4 ng for the DMI‐resistant allele. The detection limits of qPCR protocols (LOD) ranged from 0.72 to 0.85%, and the quantification limits (LOQ) ranged from 2.4 to 2.85% for the two alleles G47A and Y136F respectively. The application of qPCR to field isolates from French vineyards showed the presence of DMI‐resistant and/or QoI‐resistant alleles in French pathogen populations, linked to genetic group B. CONCLUSION: The real‐time PCR assay developed in this study provides a potentially useful tool for efficient quantification of different alleles of interest for fungicide monitoring and for population structure of E. necator. Copyright © 2010 Society of Chemical Industry     

Decreasing azole sensitivity of Z. tritici in Europe contributes to reduced and varying field efficacy

Journal of Plant Diseases and Protection - Septoria tritici blotch (STB; Zymoseptoria tritici) is the most important leaf disease of wheat in Northern and Western Europe. The problem of fungicide...     

Sensitivity of Podosphaera aphanis isolates to DMI fungicides: distribution and reduced cross‐sensitivity

BACKGROUND: Management of strawberry powdery mildew, Podopshaera aphanis (Wallr.), requires numerous fungicide treatments. Limiting epidemics is heavily dependent on sterol demethylation inhibitors (DMIs) such as myclobutanil or penconazole. Recently, a noticeable reduction in the efficacy of these triazole fungicides was reported by strawberry growers in France. The goal of this study was to investigate the state of DMI sensitivity of French P. aphanis and provide tools for improved pest management. RESULTS: Using leaf disc sporulation assays, sensitivity to myclobutanil and penconazole of 23 isolates of P. aphanis was monitored. Myclobutanil EC₅₀ ranged from less than 0.1 to 14.67 mg L^?1 and for penconazole from 0.04 to 4.2 mg L^?1. A cross‐analysis and a Venn diagram showed that there was reduced sensitivity and a positive correlation between the less sensitive myclobutanil and penconazole isolates; 73.9% of isolates were less sensitive to a DMI and 47.8% exhibited less sensitivity to both fungicides. CONCLUSION: The results show that sensitivity to myclobutanil and, to a lesser extent, penconazole has become less efficient in strawberry powdery mildew in France. Therefore, urgent action is required in order to document its appearance and optimise methods of control. Copyright © 2009 Society of Chemical Industry     

Influence of storage approaches on instability of propiconazole resistance in Monilinia fructicola

BACKGROUND: The long‐term preservation of interesting phenotypes in plant pathogenic fungi allows for follow‐up studies in the future. Twelve storage approaches were investigated to determine their effects on instability of propiconazole resistance for three demethylation inhibitor (DMI) fungicide‐resistant and two DMI‐sensitive isolates of Monilinia fructicola. They included mycelium in PDA slants under mineral oil, in PDA plugs under 10% glycerol, on dried filter paper and conidia on silica gel, each stored for 36 weeks at 4, ? 20, and ? 80 °C. RESULTS: None of the storage approaches prevented the rapid decline of EC₅₀ values for propiconazole in the three resistant isolates, and no significant differences were found among storage approaches (P = 0.787) or between storage approaches and consecutive transfers (P = 0.053). Most of the decline in resistance occurred during the first 4 weeks of storage. The DMI resistance‐associated genetic element Mona, located in the immediate upstream region of the MfCYP51 gene, was still present in the three resistant isolates after 36 weeks of storage and weekly transfers. Furthermore, the Mona element and a portion of the MfCYP51 gene, which encodes the target enzyme for DMIs, did not reveal signs of DNA methylation. Resistance to propiconazole was partially regained in resistant isolates after two growth cycles on fresh peach fruit. CONCLUSIONS: Obtained data indicate that the decline of DMI resistance in M. fructicola cannot be prevented using commonly employed storage methods at various temperatures. The number of consecutive transfers and the storage duration prior to fungicide sensitivity tests in M. fructicola should be indicated in scientific papers. Copyright © 2011 Society of Chemical Industry     

The benefits of combining elemental sulfur with a DMI fungicide to control Monilinia fructicola isolates resistant to propiconazole

BACKGROUND: Management of demethylation inhibitor (DMI) fungicide resistance in Monilinia fructicola (G. Winter) Honey is a priority in peach orchards of the southeastern United States, but DMI fungicides are still an important component of antiresistance strategies in view of the few effective alternatives. The goal of this study was to investigate potential benefits of a sulfur/propiconazole mixture for the control of propiconazole-resistant isolates.RESULTS: The mixture provided the best control for propiconazole-resistant isolates, regardless of protective or curative application timings, or the presence or absence of fruit injury. Propiconazole-resistant isolates developed disease on detached fruit after protective or curative applications of propiconazole or its mixture with sulfur, but protective applications of the mixture significantly reduced (P = 0.05) disease symptoms compared with the individual compounds. Additive to slightly synergistic effects were observed for the mixture in protective treatments of peaches inoculated with propiconazole-resistant isolates.CONCLUSION: The results suggest that the addition of elemental sulfur to a DMI fungicide is likely to be a relatively inexpensive means to improve brown rot control in peach production areas where reduced sensitivity to DMI fungicides is suspected but has not led to noticeable control failure.     

The effects of various plant protection methods on the development of Zymoseptoria tritici and Cephalosporium gramineum,grain yield and protein profile

Septoria leaf blotch progresses rapidly, leading to the development of Zymoseptoria titici forms resistant to fungicides. Cephalosporium stripe is caused by Cephalosporium gramineum. The aim of this study was to evaluate the effectiveness of selected pesticides in limiting the symptoms of both diseases on winter wheat leaves, and to determine their influence on grain yield and the content and composition of protein fractions in wheat kernels. Propiconazoles were most effective in inhibiting the development of Septoria leaf blotch (symptoms were reduced from 54.7% to 78.6%). Strobilurins were less effective due to the presence of isolates with the G143A mutation. Symptoms of Cephalosporium stripe were rarely observed, and protective treatments did not reduce their severity. The highest content of grain protein (14.81%) was found in plants most intensely protected with the fungicides containing fenpropimorph, pyraclostrobin and epoxiconazole. The principal component analysis revealed that the plant protection method influenced the grain protein profile. The accumulation of HMW glutenins and α/β gliadins was mutually interrelated and higher in high-input treatments; control grain was characterized by close relationships between ω-gliadins, LMW glutenins, albumins and globulins, whereas low-input treatments influenced mostly γ-gliadins.     

Detection and Quantification of Resistance of Venturia inaequalis Populations to Sterol Demethylation Inhibitors

ABSTRACT Monoconidial isolates of Venturia inaequalis were collected in 1990 and 1991 from orchards in New York, Michigan, and Nova Scotia that had never or only sporadically been treated with fungicides acting as sterol demethylation inhibitors (DMIs). Sensitivities of isolates to two representative DMIs (fenarimol and myclobutanil) were determined by a sensitivity test based on the relative growth (RG) of mycelial colonies at one discriminatory dose. Mean isolate sensitivities were not significantly different (P > 0.2) for the majority of the populations tested, and all sensitivity data obtained from these sites were combined to provide a baseline distribution of isolate sensitivities for both fenarimol and myclobutanil. The baseline distributions were compared with isolate sensitivities determined for an experimental orchard in Nova Scotia with a documented case of DMI resistance and for a commercial orchard in Michigan with a long history of DMI use and first evidence of practical DMI resistance. For both DMIs tested and in both treated orchards, frequencies of isolates with RG values <80 had decreased or only slightly increased compared to the baseline population. In contrast, frequencies of isolates with RG values >80 had increased more than 20-fold over baseline levels. Thus, isolates with RG values >80 were rated DMI resistant. The validity of a qualitative isolate classification was tested in controlled infection studies. At doses of fenarimol and myclobutanil recommended for commercial control of apple scab, reproduction of a typical sensitive isolate on treated apple leaves was suppressed completely. Lesions caused by a resistant isolate continued to expand and produced abundant conidia. Statistical analysis of orchard sensitivities revealed that the analysis of isolate counts grouped into the categories DMI sensitive or resistant was most indicative in comparisons of orchard sensitivities aimed at detection of practical DMI resistance. A high degree of cross-resistance between fenarimol and myclobutanil indicated that sensitivity tests with one of the DMIs employed as the diagnostic tool in this study can serve as a test for other DMIs.     

Sensitivities to DMI fungicides in populations of Podosphaera fusca in south central Spain

BACKGROUND: Cucurbit powdery mildew elicited by Podosphaera fusca (Fr.) U Braun & N Shishkoff limits crop production in Spain. Disease control is largely dependent on fungicides such as sterol demethylation inhibitors (DMIs). Fungicide resistance is an increasing problem in this pathogen. To overcome such risk, it is necessary to design rational control programmes based upon knowledge of field resistance. The aim of this study was to investigate the state of DMI sensitivity of Spanish P. fusca populations and provide tools for improved disease management. RESULTS: Using a leaf‐disc assay, sensitivity to fenarimol, myclobutanil and triadimenol of 50 isolates of P. fusca was analysed to determine discriminatory concentrations between sensitive and resistant isolates. As no clearly different groups of isolates could be identified, discriminatory concentrations were established on the basis of maximum fungicide field application rate, 100 mg L^?1 for the three fungicides tested. Subsequently, a survey of DMI resistance was carried out in different provinces located in the south central area of Spain during the cucurbit growing seasons in 2002, 2003 and 2004. Examination of a collection of 250 isolates revealed that 23% were resistant to fenarimol and 7% to triadimenol, the provinces of Almería, Badajoz and Murcia being the locations with the highest frequencies of resistance. By contrast, no resistance to myclobutanil was found. CONCLUSION: Results show that fenarimol and, to a lesser extent, triadimenol have become less efficient for controlling cucurbit powdery mildew in Spain. These are important observations that should lead to reconsideration of the current disease management programmes. Copyright © 2010 Society of Chemical Industry     

Are azole fungicides losing ground against Septoria wheat disease? Resistance mechanisms in Mycosphaerella graminicola

There has been a recent rapid decline in the efficacy of some, but not all, azole fungicides in controlling the Septoria leaf blotch pathogen of wheat, Mycosphaerella graminicola. Hans J. Cools and Bart A. Fraaije ask the question: can widespread resistance to all azoles develop in this pathogen? Copyright © 2008 Society of Chemical Industry     

Occurrence, Distribution, and Polymerase Chain Reaction-Based Detection of Resistance to Sterol Demethylation Inhibitor Fungicides in Populations of Blumeriella jaapii in Michigan

ABSTRACT The intensive use of site-specific fungicides in agricultural production provides a potent selective mechanism for increasing the frequency of fungicide-resistant isolates in pathogen populations. Practical resistance occurs when the frequency and levels of resistance are great enough to limit the effectiveness of disease control in the field. Cherry leaf spot (CLS), caused by the fungus Blumeriella jaapii, is a major disease of cherry trees in the Great Lakes region. The site-specific sterol demethylation inhibitor fungicides (DMIs) have been used extensively in the region. In 2002, CLS control failed in a Michigan orchard that had used the DMI fenbuconazole exclusively for 8 years. That control failure and our observations from around the state suggested that practical resistance had developed in B. jaapii. Field trial data covering 1989 to 2005 for the DMIs fenbuconazole and tebuconazole supported observations of reduced efficacy of DMIs for controlling CLS. To verify the occurrence of fungicide-resistant B. jaapii, monoconidial isolates were collected in two surveys and tested using a fungicide-amended medium. In one survey, 137 isolates from sites with different DMI histories (no known history, mixed or alternated with other fungicides, and exclusive use) were tested against 12 concentrations of fenbuconazole, tebuconazole, myclobutanil, and fenarimol. Isolates from sites with no prior DMI use were DMI sensitive (DMI(S) = no colony growth at 0.2 mug/ml a.i.) whereas the isolates from the site with prior exclusive use showed growth at DMI concentrations 3 to >100 times higher, and were rated as DMI resistant (DMI(R)). A second survey examined 1,530 monoconidial isolates, including 1,143 from 62 orchard sites in Michigan, where DMIs had been used to control CLS. Resistance to fenbuconazole was detected in 99.7% of the orchard isolates. All isolates from wild cherry trees were sensitive and isolates from feral and dooryard trees showed a range of sensitivities. A polymerase chain reaction (PCR)-based detection method for identifying B. jaapii and DMI(R) was developed and tested. The species-specific primer pair (Bj-F and Bj-R) based on introns in the CYP51 gene of B. jaapii, and the DMI(R)-specific primer pair (DMI-R-Bj-F and DMI-R-Bj-R) based on an insert found upstream of CYP51 in all DMI(R) isolates, provided an accurate and rapid method for detecting DMI(R) B. jaapii. The PCR-based identification method will facilitate timely decision making and continued monitoring of DMI(R) subpopulations in response to management programs.     

Inheritance of Race-Specific Resistance to Mycosphaerella graminicola in Wheat

ABSTRACT Mycosphaerella graminicola causes Septoria tritici blotch of hexaploid and tetraploid wheat. The inheritance of high-level resistance to Septoria tritici blotch was studied in controlled environment experiments. Intraspecific reciprocal crosses were made between hexaploid wheat lines Salamouni, ST6, Katepwa, and Erik, and the tetraploid wheat lines Coulter and 4B1149. Parental, F(1), F(2), F(3), BC(1)F(1), and BC(1)F(2) populations were evaluated for reaction to isolates MG2 and MG96-36 of M. graminicola. Resistance was controlled by incompletely dominant nuclear genes in all cases. Salamouni had three independent resistance genes to isolate MG2, two of which also controlled resistance to isolate MG96-36. ST6 had a single resistance gene to isolate MG2 and none to isolate MG96-36. The resistance genes in Salamouni and ST6 were not allelic. Two independent genes control resistance to isolate MG2 in Coulter, one of which also controlled resistance to isolate MG96-36. These data are consistent with a gene-for-gene interaction in the wheat-M. graminicola pathosystem.     

Efficacy of triazole-based fungicides for fusarium head blight and deoxynivalenol control in wheat: a multivariate meta-analysis

The effects of propiconazole, prothioconazole, tebuconazole, metconazole, and prothioconazole+tebuconazole (as a tank mix or a formulated premix) on the control of Fusarium head blight index (IND; field or plot-level disease severity) and deoxynivalenol (DON) in wheat were determined. A multivariate random-effects meta-analytical model was fitted to the log-transformed treatment means from over 100 uniform fungicide studies across 11 years and 14 states, and the mean log ratio (relative to the untreated check or tebuconazole mean) was determined as the overall effect size for quantifying fungicide efficacy. Mean log ratios were then transformed to estimate mean percent reduction in IND and DON relative to the untreated check (percent control: C(IND) and C(DON)) and relative to tebuconazole. All fungicides led to a significant reduction in IND and DON (P < 0.001), although there was substantial between-study variability. Prothioconazole+tebuconazole was the most effective fungicide for IND, with a C(IND) of 52%, followed by metconazole (50%), prothioconazole (48%), tebuconazole (40%), and propiconazole (32%). For DON, metconazole was the most effective treatment, with a [Formula: see text](DON) of 45%; prothioconazole+tebuconazole and prothioconazole showed similar efficacy, with C(DON) values of 42 and 43%, respectively; tebuconazole and propiconazole were the least effective, with C(DON) values of 23 and 12%, respectively. All fungicides, with the exception of propiconazole, were significantly more effective than tebuconazole for control of both IND and DON (P < 0.001). Relative to tebuconazole, prothioconazole, metconazole, and tebuconzole+prothioconzole reduced disease index a further 14 to 20% and DON a further 25 to 29%. In general, fungicide efficacy was significantly higher for spring wheat than for soft winter wheat studies; depending on the fungicide, the difference in percent control between spring and soft winter wheat was 5 to 20% for C(IND) and 7 to 16% for C(DON). Based on the mean log ratios and between-study variances, the probability that IND or DON in a treated plot from a randomly selected study was lower than that in the check by a fixed margin was determined, which confirmed the superior efficacy of prothioconazole, metconazole, and tebuconzole+prothioconzole for Fusarium head blight disease and toxin control.     

Quantifying the effects of fungicides and disease resistance on greenhouse gas emissions associated with wheat production

A method is presented to quantify the net effect of disease management on greenhouse gas (GHG) emissions per hectare of crop and per tonne of crop produce (grain, animal feed, flour or bioethanol). Calculations were based on experimental and survey data representative of UK wheat production during the period 2004–06. Elite wheat cultivars, with contrasting yields and levels of disease resistance, were compared. Across cultivars, fungicides increased yields by an average of 1·78 t ha^?1 and GHG emissions were reduced from 386 to 327 kg CO₂ eq. t^?1 grain. The amount by which fungicides increased yield – and hence reduced emissions per tonne – was negatively correlated with cultivar resistance to septoria leaf blotch (Mycosphaerella graminicola, anamorph Septoria tritici). GHG emissions of treated cultivars were always less than those of untreated cultivars. Without fungicide use, an additional 0·93 Mt CO₂ eq. would be emitted to maintain annual UK grain production at 15 Mt, if the additional land required for wheat production displaced other UK arable crops/set aside. The GHG cost would be much greater if grassland or natural vegetation were displaced. These additional emissions would be reduced substantially if cultivars had more effective septoria leaf blotch resistance. The GHGs associated with UK fungicide use were calculated to be 0·06 Mt CO₂ eq. per annum. It was estimated that if it were possible to eliminate diseases completely by increasing disease resistance without any yield penalty and/or developing better fungicides, emissions could theoretically be reduced further to 313 kg CO₂ eq. t^?1 grain.     

Characterization of CbCyp51 from field isolates of Cercospora beticola

The hemibiotrophic fungus Cercospora beticola causes leaf spot of sugar beet. Leaf spot control measures include the application of sterol demethylation inhibitor (DMI) fungicides. However, reduced sensitivity to DMIs has been reported recently in the Red River Valley sugar beet-growing region of North Dakota and Minnesota. Here, we report the cloning and molecular characterization of CbCyp51, which encodes the DMI target enzyme sterol P450 14α-demethylase in C. beticola. CbCyp51 is a 1,632-bp intron-free gene with obvious homology to other fungal Cyp51 genes and is present as a single copy in the C. beticola genome. Five nucleotide haplotypes were identified which encoded three amino acid sequences. Protein variant 1 composed 79% of the sequenced isolates, followed by protein variant 2 that composed 18% of the sequences and a single isolate representative of protein variant 3. Because resistance to DMIs can be related to polymorphism in promoter or coding sequences, sequence diversity was assessed by sequencing >2,440 nucleotides encompassing CbCyp51 coding and flanking regions from isolates with varying EC(50) values (effective concentration to reduce growth by 50%) to DMI fungicides. However, no mutations or haplotypes were associated with DMI resistance or sensitivity. No evidence for alternative splicing or differential methylation of CbCyp51 was found that might explain reduced sensitivity to DMIs. However, CbCyp51 was overexpressed in isolates with high EC(50) values compared with isolates with low EC(50) values. After exposure to tetraconazole, isolates with high EC(50) values responded with further induction of CbCyp51, with a positive correlation of CbCyp51 expression and tetraconazole concentration up to 2.5 μg ml(-1).     

Sensitivity of Rhizoctonia solani causing rice sheath blight to fluxapyroxad in China

Fluxapyroxad,3-(difluoromethyl)-1-methyl-N-(3’,4’,5’-trifluorobiphenyl-2-yl) pyrazole-4-carboxamide (C₁₈H₁₂F₅N₃O, Fig. 1), is a SDHI fungicide, which is a new active ingredient that interferes with succinate ubiquinone reductase in the electron transport chain of fungi. Between 2008 and 2010, a total of 128 isolates of Rhizoctonia solani from Anhui Province of China were characterized for the baseline sensitivity to fluxapyroxad. The isolates collected between 2008 and 2010 all showed similar sensitivity to fluxapyroxad. Baseline sensitivity was distributed as unimodal curves with an average EC₅₀ value of 0.054?±?0.014 μg ml^?1. However, EC₅₀ values of boscalid for inhibition of mycelial growth of R. solani isolates ranged from 1.89 to 2.68 μg/ml and the average (±SE) EC₅₀ value was 2.212?±?0.228 μg/ml, indicating that the R. solani isolates were less sensitive to boscalid than that of fluxapyroxad. Fluxapyroxad exhibited excellent protective and curative activity against rice sheath blight and provided 82.6–94.2 % protective or curative control efficacy. In field trials, control efficacy of fluxapyroxad at 100 g a.i/ha 15 days and 30 day after second application was 83.4–88.0 %, suggesting excellent activity against sheath blight. Control efficacy of boscalid at a dosage of 600 g a.i/ha 15 days and 30 day after second application was about 51.7–57.0 %. There was a significant difference in the efficacy between fluxapyroxad and boscalid or jinggangmycin. These results suggested that fluxapyroxad is a good alternative fungicide to jinggangmycin for the control of rice sheath blight.     

Research on Septoria Leaf Blotch: Recent Advances1

A review of the recent advances in research on Septoria leaf blotch is given with particular emphasis on epidemiology and control strategies. The effect of straw infected with pycnidia of Septoria tritici or perithecia of its perfect stage Mycosphaerella graminicola , infected seeds and alternative hosts on the initiation of epidemics is discussed. Reference is made to the effect of plant stature on the vertical progress of the disease. The role of fungicide protection in the control of the disease is discussed. Resistance and tolerance to Septoria leaf blotch is dealt with in more detail, with reference to the author's own research, and with implications on breeding strategies.