Studies on the Interaction Between Septoria tritici and Stagonospora nodorum in Wheat

Interactions between Stagonospora nodorum and Septoria tritici were studied. Results from a detached glume experiment indicated that the interaction may be isolate-dependent, as it was shown that the interaction between the two pathogens may be beneficial or antagonistic depending on the isolate of each pathogen present. The number of spores produced by both pathogens was significantly greater when an aggressive isolate of S. tritici was mixed with a non-aggressive isolate of S. nodorum, whereas the number of spores produced by both pathogens was significantly less when two non-aggressive isolates were mixed. There was a significant reduction in disease level when S. tritici was applied prior to S. nodorum, compared to vice versa in the growth chamber. Results from growth chamber and field studies showed that S. nodorum produced significantly more spores when both pathogens were present together. It is concluded that S. tritici has a stimulatory effect on spore production by S. nodorum. However, there was a reduction of S. tritici spores observed in the dual inoculation treatments, suggesting that S. nodorum inhibits S. tritici.     

Survey of cereal diseases and petts in the Netherlands. 5. Occurrence of Septoria spp. in winter wheat

Data of the annual surveys of circa 100 commerical winter wheat fields were compiled to describe epidemics ofSeptoria spp. in the Netherlands during 1974–1986. In May, during the first node stage,S. tritici was dominant whileS. nodorum was virtually absent. In July, during ripening,S. tritici on average dominated overS. nodorum, though in the most continental districts of the countryS. nodorum predominated.In May between 1974 and 1984, on average 56% of the fields showed leaf infections bySeptoria spp., while in July between 1975 and 1986, on average 83% of the fields showed leaf infections. Prevalence ofSeptoria spp. has increased during the surveys. Annual intensity ofSeptoria spp. in winter wheat crops was positively correlated with precipitation and negatively with average monthly sunshine duration during the harvest-month August of the previous growing season. The correlation with sunshine during August could indicate that ascospores play a major role in subsequent epidemics; but whether it is a causal relation remains to be answered.Present address: Center for Agrobiological Research (CABO-DLO), PO Box 14, 6700 AA Wageningen, the Netherlands     

Temperature Dependent Seed Transmission of Stagonospora nodorum in Wheat

The transmission of Stagonospora nodorum from four naturally infected winter wheat seedlots was quantified in controlled environment germination chambers at 9, 13, 17, 21, and 25 °C. Seedlings were harvested when the second leaf began to emerge. Coleoptiles and first seedling leaves were examined for the presence of lesions caused by S. nodorum. First leaves were incubated on Bannon's medium for 2 weeks, after which they were examined for pycnidia of S. nodorum. Transmission to the coleoptile occurred at all temperatures, but decreased from 100% to 72% as temperature increased from 9 to 25 °C. Transmission to the first leaf was less, dropping from 37% to 2% as temperature increased from 9 to 25 °C. At least 44% of infected first leaves were symptomless at all temperatures, with 96% of infected leaves showing no symptoms at 25 °C. Transmission to seedling leaves occurred over a broad temperature range. Under the high densities at which wheat is sown, a significant number of infected seedlings per unit area may originate from relatively low initial seed infection levels and transmission efficiencies.     

Yield Reduction in Wheat in Relation to Leaf Disease From Yellow (tan) Spot and Septoria Nodorum Blotch

Yellow or tan spot (caused by Pyrenophora tritici-repentis) and septoria nodorum blotch (caused by Phaeosphaeria nodorum) occur together and are a constraint to wheat yields in Australia. Recently, higher crop yields and lower fungicide costs have made fungicides an attractive management tool against these diseases. Yield-loss under different rates of progress of yellow spot and septoria nodorum blotch was examined in four experiments over three years to define the relationship between disease severity and yield. In these experiments, differences in disease were first promoted by inoculations either with P. tritici-repentis-infected stubble or aqueous spore suspensions of P. nodorum. Disease progress was further manipulated with foliar application of fungicide. The pattern of disease development varied in each year under the influence of different rainfall patterns. The inoculation and fungicide treatments produced differences in disease levels after flag leaf emergence. The infection of yellow spot or septoria nodorum blotch caused similar losses in grain yield, ranging from 18% to 31%. The infection by either disease on the flag or penultimate leaf provided a good indication of yield-loss. Disease severity on flag leaves during the milk stage of the crop or an integration of disease as area under the disease progress curve on the flag leaves based on thermal time explained more than 80% variance in yield in a simple regression model. The data provided information towards the development of disease management strategies for the control of septoria nodorum blotch and yellow spot.     

模拟酸雨对小麦条锈病流行学组分的影响

为明确酸雨对小麦条锈病菌孢子萌发及病害流行学组分的影响,采用不同酸度的模拟酸雨(p H值分别为2.5、3.5、4.5和5.6)处理小麦条锈病菌Puccinia striiformis f.sp.tritici生理小种CYR32和CYR33的夏孢子,并将不同酸度模拟酸雨处理后的夏孢子接种小麦感病品种铭贤169,采用组分分析法研究酸雨对病害发展过程的影响。结果表明,随着模拟酸雨酸度的增强,生理小种CYR32和CYR33的夏孢子萌发率均显著降低,萌发24 h后对照组生理小种CYR32和CYR33的夏孢子萌发率分别为93.7%和79.8%,在p H 3.5模拟酸雨处理后萌发率仅为13.1%和8.6%。温室内接种试验结果显示,不同酸度模拟酸雨对生理小种CYR32和CYR33的侵染概率、潜育期和病情指数均有显著影响,对生理小种CYR32和CYR33病斑扩展率影响不显著;与对照相比,p H 3.5模拟酸雨处理后生理小种CYR32和CYR33的侵染概率分别下降79.9%和79.8%。结果表明强酸雨(p H 3.5)显著延长小麦条锈菌潜育期,减少病斑产孢量,降低病情指数和病害进展曲线下面积。     

Prior Inoculation with Non-pathogenic Fungi Induces Systemic Resistance to Powdery Mildew On Cucumber Plants

A spray inoculation of the first leaf of 2-leaf stage cucumber plants with a non-pathogenic isolate of Alternaria cucumarina or Cladosporium fulvum before a challenge inoculation with the pathogen Sphaerotheca fuliginea induced systemic resistance to powdery mildew on leaves 2–5. Systemic resistance was expressed by a significant (p < 0.05) reduction in the number of powdery mildew colonies produced on each leaf of the induced plants, as compared with water-sprayed plants. Systemic resistance was evident when a prior inoculation with each of the inducing fungi was administered 1, 3 or 6 days before the challenge inoculation with S. fuliginea. Increasing the inoculum concentration of A. cucumarina or C. fulvum enhanced the systemic protection and provided up to 71.6% or 80.0% reduction, respectively, in the number of colonies produced on upper leaves, relative to controls. Increasing the inoculum concentration of S. fuliginea used for challenge inoculation, increased the number of powdery mildew colonies produced on both induced and non-induced plants. Pre-treated plants, however, were still better protected than controls, indicating that the level of systemic protection was related to the S. fuliginea inoculum concentration. The induction of systemic resistance against powdery mildew by biotic agents, facilitates the development of a wide range of disease management tools.     

Analysis of Accumulation Patterns of <Emphasis Type="Italic">Barley yellow dwarf virus-PAV</Emphasis> (BYDV-PAV) in Two Resistant Wheat Lines

Barley yellow dwarf (BYD) is one of the main viral diseases of small-grain cereals. This disease, reported on numerous plant species of the Poaceae family, is caused by a complex of eight viral species including the species Barley Yellow Dwarf Virus-PAV (BYDV-PAV), frequently found in western Europe. Resistance sources against BYDV-PAV are scarce and only identified in perennial Triticineae. Some BYDV-resistant wheat lines have been obtained by introgressing these resistances into bread wheat germplasms. Genetic and biological characterization of the resulting lines has been undertaken. However, little information on the resistant behaviour of these lines during the early stages of the infection process is available. To evaluate the resistance of two genetically distinct resistant lines (Zhong ZH and TC14), 1740 young plantlets, belonging to susceptible reference hosts (barley cv. Express and wheat cv. Sunstar), Zhong ZH or TC14 wheat lines, were inoculated in controlled conditions with French BYDV-PAV isolates. The infection process was monitored during the first 21 days after inoculation (DAI) using a semi-quantitative ELISA. A standardized protocol including five successive samplings of leaves from all inoculated plants and the collection of plant roots at the end of the monitored period was carried out. This protocol enabled an assessment of the infection percentage and the evolution of the viral load in plants from the 7th DAI to the 21st DAI. Statistical analyses of the BYDV infection kinetics using raw ELISA data, a model of the time-dependent variation of the percentage of infected plants and the area under concentration progress curves (AUCPC) demonstrated that Zhong ZH and TC14 lines (1) reduce the development rate of the BYD disease during the first days of infection, (2) decrease the infection efficiency of BYDV-PAV isolates, in the leaves, from 98.7% for susceptible plant genotypes to 81.9% and 71.7% for Zhong ZH and TC14, respectively, (3) reduce the virus load in the leaves of infected plants and (4) are not spared from BYDV infection, as 95.1% of Zhong ZH and 90.2% of TC14 inoculated plants accumulated viral particles in roots and/or in leaves at 21 DAI. These results confirm the BYDV-partial resistant behaviour of both Zhong ZH and TC14 lines. The development rate of the disease was the single parameter that allowed the distinction between the two resistant sources present in the tested lines.     

Note: Occurrence ofMycosphaerella graminicola, teleomorph ofSeptoria tritici, in Slovakia

Pseudothecia ofMycosphaerella graminicola, the teleomorph ofSeptoria tritici, were observed on leaves of winter wheat (Triticum aestivum L.) in Slovakia for the first time in 2004. The samples of this pyrenomycetous ascomycete were compared with previously published data by micrometric characteristics using light microscope observations of morphological characteristics. http://www.phytoparasitica.org posting July 18, 2005.     

The development of a PCR-based method for detecting <Emphasis Type="Italic">Puccinia striiformis</Emphasis> latent infections in wheat leaves

Stripe rust of wheat caused by Puccinia striiformis f. sp. tritici is one of the most important diseases on wheat worldwide, especially in temperate regions with cool moist weather conditions. A rapid and reliable detection of the pathogen in latent infected wheat leaves during overwintering of the fungus in the dormant stage will contribute to determine the initial inoculum potential and thus to predict early outbreak and to improve effective management of the disease. To achieve this aim, a PCR-based method was developed for specific and sensitive detection of P. striiformis. Specific primers were designed according to a genome-specific sequence of P. striiformis. To evaluate the specificity of the primers, seven different isolates and races of P. striiformis as well as six other pathogens of wheat were tested. All isolates of P. striiformis yielded a distinct band of a fragment of 470 bp, while using DNA of the other wheat pathogens as a template no amplification product was detected. The sensitivity of the primers was tested using serial dilutions of total DNA from P. striiformis; the limit of detection was 10 pg of DNA. Using extracts from P. striiformis-infected wheat leaves, the fungus could be determined in the leaves before symptoms appeared. The stripe rust could also be detected in the dormant stage by the PCR assay in samples of wheat leaves taken during the winter season. The application of the PCR assay may be useful for rapid and reliable detection of P. striiformis in latent infected leaves of overwintering wheat plants.     

Effect of adjuvants on the performance of the new cereal fungicide,metconazole. II Field trials

Glasshouse trials had shown that the activity of metconazole formulations against cereal foliar diseases could be enhanced by alcohol ethoxylate adjuvants. A series of soluble liquid (SL) formulations of metconazole had been prepared containing adjuvant: metconazole ratios of 5:1, 7.5:1, 10:1, 15:1 m/m (SL1, SL2, SL3, SL4) which glasshouse trials had shown could give equivalent performance to an emulsifiable concentrate formulation, (ECM) of metconazole at application rates up to three- or four-fold lower than that of ECM alone. A field trials programme was undertaken to compare the performances of these SL formulations with ECM at 120 g AI ha^?1, through a range of application rates (48, 60, 72, 84 g AI ha^?1), in a non-orthogonal factorial trial design against diseases that occurred naturally (Septoria tritici Rob., Puccinia recondita Rob., Pyrenophora teres Drechs., Erysiphe graminis DC) or by artificial inoculation (Leptosphaeria nodorum Muell.), on either Triticum aestivum L. or Hordeum vulgare L. The results from trials in three locations showed that the commercially acceptable performance of ECM at 120 g AI ha^?1, in giving high levels of control of P. recondita, S. tritici and L. nodorum (both prophylactic and therapeutic activity) on T. aestivum. and of E. graminis and P. teres on H. vulgare, could be matched or improved by SL2, SL3 and SL4 at 72 g AI ha^?1. Furthermore, control of E. graminis f. sp. tritici Marchal by these SL formulations at this application rate was better than that by ECM at 120 g AI ha^?1, though the levels of control still remained below commercial acceptability for therapeutic activity. Nevertheless, substantial reductions in the application rate of metconazole have been achieved by using one-pack adjuvant-containing formulations in field trials, while still maintaining excellent control of a range of cereal foliar diseases. The choice between these SL formulations could therefore be made on other grounds such as cost/performance and ease of formulation.     

Use of carbendazim and carbendazim-resistant yeasts to create different yeast densities on wheat leaves for field studies on biological control

Phyllosphere yeasts may play an important role in suppressing necrotrophic pathogens. In a randomized block design, yeast densities on flag leaves and second leaves of field-grown wheat were left unchanged (D), or were lowered by sprayings with carbendazim (A), or were raised by sprayings with a mixture ofSporobolomyces roseus, Cryptococcus laurentii var.flavescens and nutrients (B), or with carbendazim, carbendazim-resistantS. roseus andC. laurentii var.flavescens and nutrients (C). The application of carbendazim to plots A and C would avoid a biased interference of carbendazim due to other effects than reducing the natural yeast population. Prolonged differences in yeast density would be reflected in differences in severity of diseases caused by carbendazim-insensitive necrotrophic pathogens.Both treatments B and C enhanced the yeast density about 10-fold at the beginning of leaf colonization, 2 to 3 weeks after leaf emergence. Untreated leaves (D), however, were rapidly leaves. Initially, the yeasts were suppressed by carbendazim (A). However, progressively the yeast population consisted of carbendazim-resistant strains which made the carbendazim sprayings ineffective. Therefore, the substantial differences in yeast density were of limited duration. The effect of the treatments on naturally occurringMycosphaerella graminicola (anam.Septoria tritici), Puccinia recondita f. sp.tritici and the total necrotic leaf area (D-value) is discussed.Samenvatting Fyllosfeergisten kunnen misschien een belangrijke rol spelen in de onderdrukking van necrotrofe pathogenen. In een blokkenproef werd de dichtheid van gisten op vlagbladeren en tweede bladeren niet beïvvloed (D) of verlaagd door bespuitingen met carbendazim (A), of verhoogd door bespuitingen met een mengsel van gisten (Sporobolomyces roseus enCryptococcus laurentii var.flavescens en voedingsstoffen (B), of met een mengsel van carbendazim, carbendazim-resistenteS. roseus enC. laurentii var.flavescens en voedingsstoffen (C). De grootste verschillen in dichtheden van de gistpopulaties werden verwacht tussen de behandelingen A en B of C. Door alle veldjes A en C met carbendazim te behandelen wordt een eenzijdig effect van carbendazim, berustend op andere eigenschappen dan de onderdrukking van de natuurlijke gistpopulatie, voorkomen. Langdurige verschillen in de populatiedichtheden van de gisten zouden weerspiegeld kunnen worden in verschillen in aantasting door carbendazimongevoelige necrotrofe pathogenen.Aan het begin van de bladkolonisatie door gisten, 2 tot 3 weken na het verschijnen van het blad, leidde zowel behandeling B als C tot, een 10-voudige verhoging van de gistdichtheid. De onbehandelde bladeren (D) werden echter spoedig door de van nature voorkomende gisten gekoloniseerd en het verschil tussen de onbehandelde en met gist bespoten bladeren werd snel kleiner. Aanvankelijk werden de gisten door carbendazim (A) onderdrukt. Geleidelijk bestond de gistpopulatie echter uit carbendazim-resistente stammen, zodat de carbendazim bespuitingen nauwelijks meer effect hadden. Hierdoor werden grote verschillen in gistdichtheden niet langdurig gerealiseerd. Het effect van de behandelingen op de natuurlijke infectie doorMycosphaerella graminicola (anam.Septoria tritici), Puccina recondita f. sp.tritici en op het totale dode bladoppervlak (D-waarde) wordt besproken.     

Fusarium head blight evaluation in wheat transgenic plants expressing the maize <Emphasis Type="Italic">b-32</Emphasis> antifungal gene

The maize gene b-32, normally expressed in the maize (Zea mays) endosperm, encodes for a RIP (Ribosome Inactivating Protein) characterised by antifungal activity. Transgenic wheat plants were obtained via biolistic transformation, in which the b-32 gene is driven by the 35SCaMV promoter in association with the bar gene as a selectable marker. Plants were brought to homozygosity through genetic analysis of progeny and pathogenicity tests were performed on the fourth generation. Six homozygous b-32 wheat lines were characterised. All plants had a normal phenotype, not distinguishable from the control cv. Veery except for slightly smaller size, flowered and set seeds. Western blot analyses confirmed b-32 expression during the plant life cycle in the various tissues. Each line differed in the b-32 content in leaf protein extracts and the transgenic protein expression level was maintained at least up to 10 days after anthesis. Pathogenicity tests for Fusarium head blight (FHB) were performed on the b-32 transgenic wheat lines in comparison to the parental cv. Veery. Resistance to FHB was evaluated by the single floret injection inoculation method on immature spikes with spores of Fusarium culmorum. In all the transgenic lines, a similar reduction in FHB symptoms, not dependent on the level of b-32 protein, has been observed (20% and 30% relative to the control, respectively 7 and 14 days after inoculation). Percentage of tombstone kernels at maturity was also recorded; in all transgenic lines disease control for this parameter was around 25%. The data obtained indicate that maize b-32 was effective as in vivo antifungal protein reducing FHB symptoms in wheat lines expressing the maize RIP protein.     

The effect of potential resistance inducers on development of <Emphasis Type="Italic">Microdochium majus</Emphasis> and <Emphasis Type="Italic">Fusarium culmorum</Emphasis> in winter wheat

The effect of potential resistance inducing chemicals on disease development of Fusarium head blight was studied in winter wheat (Triticum aestivum L.). As a pre-screening test, the effect of different treatments on development of Microdochium majus (syn. Microdochium nivale var. majus) was studied in detached leaves. Based on these tests, DL-3-aminobutyric acid, Bion (benzo-(1,2,3) thiadiazole-7-carbothioic acid S-methyl ester), and a foliar fertilizer containing potassium phosphite were selected for further studies. Greenhouse-grown winter wheat was sprayed with aqueous solutions of the potential resistance inducers 7 days prior to Fusarium culmorum point inoculation of the heads. Disease development was registered as number of bleached spikelets per inoculated spike. Spraying plants with the foliar fertilizer reduced the disease severity of F. culmorum by up to 40%. A reduced disease development of M. majus was also observed in detached leaves pre-treated with the foliar fertilizer. When the foliar fertilizer was added to the growth medium, a reduced in vitro growth of M. majus and F. culmorum was observed, indicating that the effect on disease development is at least partly due to a fungistatic effect. No significant reduction in disease development was observed in wheat pre-treated with DL-3-aminobutyric acid or Bion, although these compounds tended to reduce disease development, especially when applied in combination with other potential resistance inducers. We conclude that spraying winter wheat with a solution containing potassium phosphite can reduce development of M. majus and F. culmorum.     

小麦全蚀病菌拮抗细菌的筛选及生防效果

为筛选小麦全蚀病菌Gaeumannomyces tritici的拮抗细菌,从健康小麦根际土壤中分离和筛选拮抗细菌,采用对峙培养法和室内盆栽试验测定拮抗细菌对小麦全蚀病菌的抑制活性及生防效果,通过形态学特征观察、生理生化特性测定和保守序列分析确定其分类地位。结果表明,从小麦根际土壤中分离并筛选获得2株具有较好拮抗效果的菌株XJ-3和XJ-4,对小麦全蚀病菌菌丝生长的抑制率分别为64.31%和65.25%。基于菌株XJ-3和XJ-4的形态学特征、生理生化特性和gyrB基因系统进化分析结果,将其均鉴定为贝莱斯芽胞杆菌Bacillus velezensis。菌株XJ-3和XJ-4的发酵液中均含有一类具抗真菌活性、耐热性的非蛋白类次生代谢产物;经菌株XJ-3和XJ-4发酵液处理小麦幼苗后,株高较对照分别显著增加了6.48%和13.12%,干重较对照分别增加了1.30%和14.29%,其中菌株XJ-4的促生效果相对较好;对小麦全蚀病的盆栽防效分别达到51.29%和52.46%。表明筛选得到的贝莱斯芽胞杆菌XJ-3和XJ-4可用于小麦全蚀病的生物防治,具有开发为生防制剂的潜力。     

Induction of a defense response in strawberry mediated by an avirulent strain of <Emphasis Type="Italic">Colletotrichum</Emphasis>

In the strawberry crop area of Tucumán (north-west Argentina) the three species of Colletotrichum causing anthracnose disease (C. acutatum, C. fragariae and C. gloeosporioides) were detected. Among all isolates characterized, one of them identified as C. acutatum (M11) and another as C. fragariae (F7) were selected due to their conspicuous interaction with the strawberry cultivar Pájaro. Whereas isolate M11 produced a strong compatible interaction in cv. Pájaro with clear disease symptoms (DSR = 5.0), the isolate F7 brought about a typical incompatible interaction (DSR = 1.0). When plants of cv. Pájaro were inoculated with F7 prior to the inoculation with M11, the former avirulent strain prevented the growth of the latter virulent pathogen. Experimental evidence indicated that the time elapsed between the first inoculation with the avirulent pathogen and the second inoculation with the virulent one was crucial to inhibit the growth of the latter. The growth of F7 on the plant without provoking damage and the fact that there was no in vitro antagonistic effect between the pathogens, suggests that the avirulent strain triggers a plant defensive response against M11. The defense response was further confirmed by the detection of an early oxidative burst occurring within 4 h after the first inoculation and by the observation of anatomical changes associated with defense mechanisms that lasted 50 days after the inoculation with F7. Results obtained support the hypothesis that the plant resistance against the virulent strain M11 is elicited by one or more diffusible(s) compound(s) produced by the avirulent strain F7.     

Pathogenic variation in populations of Drechslera teres f. teres and D. teres f. maculata and differences in host cultivar responses

The current study examined the variability in the pathogenicity of populations of Drechslera teres f. teres and D. teres f. maculata (the net and spot forms of D. teres) from Ireland and northern Europe. A population of progeny isolates from a mating of net and spot forms was also examined. Significant variation in virulence was found both between and among net form and spot form isolates (p<0.001). In the Irish population, significant differences were found between the net and spot forms, with the spot form isolates more virulent (p<0.05). Progeny isolates were significantly more virulent than net form or spot form populations (p<0.001). Significant differences were found in cultivar reactions, with cv. Botnia most susceptible to both forms of the pathogen (p<0.001). Cultivar Boreal 94145, although quantitatively resistant, was found to be very susceptible to both forms of the pathogen and to progeny isolates. Cultivars CI 5791, CI 2330 and CI 9819 were all less susceptible to infection by both forms, but were more susceptible to spot form isolates. Significant correlations were found between whole plants and detached leaf experiments for the net form isolates only (p<0.001). This study illustrates the importance of including both net form and spot form isolates in resistance studies and the need for a clearer understanding for the genetic basis of resistance to the net and spot forms. It also highlights the limitations of using a detached leaf assay for screening of net blotch of barley.     

Genetics of host-pathogen interactions in the <Emphasis Type="Italic">Pyrenophora teres</Emphasis> f. <Emphasis Type="Italic">teres</Emphasis> (net form) – barley (<Emphasis Type="Italic">Hordeum vulgare)</Emphasis> pathosystem

The genetics of host-pathogen interactions in the Hordeum vulgare – P. teres f. teres pathosystem was studied in twelve resistant barley accessions, i.e. CI 9825, CI 9819, Diamond, CI 4922, CI 5401, Harbin, c-8755, c-21849, c-8721 c-23874, c-19979, c-15811. F₂ analyses of crosses with susceptible genotypes employing various isolates (from Europe, USA, Canada, and Australia) revealed that resistance is mostly isolate-specific and controlled by one or two genes. Segregation in ascospore progeny from two crosses between isolates of different origin revealed that avirulence in P. teres is also determined by one or two genes. An epistatic effect of suppressor genes on avirulence genes is proposed for the genetics of virulence to Diamond, Harbin, CI 5401 and c-8721 in the fungal crosses D (181-6 × A80) and F (H-22 × 92-178/9). Segregation in F₂ of crosses of three new sources of resistance (c-23874, c-19979, c-15811) to the susceptible cv. Pirkka was studied in laboratory and greenhouse tests by using seven P. teres isolates, i.e. 181-6, d8-3, d8-4, d9-1, d9-4, F4 and F74. In addition, virulence to these barley accessions of ascospore progeny from crosses of the same isolates was studied. Based on these studies it was concluded that depending on the isolate used, resistance of c-23874 is determined at least by two genes and in c-19979 and c-15811 by three genes. The results of this parallel analyses of genetics of resistance and genetics of virulence allows the postulation of a gene–for–gene interaction in the P. teres – H. vulgare pathosystem.     

Temporal and spatial field evaluations highlight the importance of the presymptomatic phase in supporting strong partial resistance in Triticum aestivum against Zymoseptoria tritici

Zymoseptoria tritici, the causal agent of septoria tritici blotch (STB), remains a significant threat to European wheat production with the continuous emergence of fungicide resistance in Z. tritici strains eroding the economic sustainability of wheat production systems. The life cycle of Z. tritici is characterized by a presymptomatic phase (latent period, LP) after which the pathogen switches to an aggressive necrotrophic stage, when lesions bearing pycnidia quickly manifest on the leaf. As minimal knowledge of the possible role of the LP in supporting STB resistance/susceptibility exists, the goal of this study was to investigate the spatial and temporal association between the LP and disease progression across three locations (Ireland – Waterford, Carlow; UK – Norwich) that represent commercially high, medium and low STB pressure environments. Completed over two seasons (2013–2015) with commercially grown cultivars, the potential of the LP in stalling STB epidemics was significant as identified with cv. Stigg, whose high level of partial resistance was characterized by a lengthened LP (c. 36 days) under the high disease pressure environment of Waterford. However, once the LP concluded it was followed by a rate of disease progression in cv. Stigg that was comparable to that observed in the more susceptible commercial varieties. Complementary analysis, via logistic modelling of intensive disease assessments made at Carlow and Waterford in 2015, further highlighted the value of a lengthened LP in supporting strong partial resistance against STB disease of wheat.     

Sulphate and sulphurous acid alter the relative susceptibility of wheat to Phaeosphaeria nodorum and Mycosphaerella graminicola

The relative abundances of DNA of Mycosphaerella graminicola and Phaeosphaeria nodorum in archived wheat samples are closely correlated with UK anthropogenic emissions of oxidized sulphur over the last 160 years. To test whether this could be a causal relationship, possible modes of action of sulphur on the two fungi were examined. Mycelial growth of the two fungi in solutions of sulphurous acid was similar. Sulphurous acid at pH 4 reduced percentage germination of P. nodorum conidia more strongly than M. graminicola conidia. In spray inoculations of wheat cv. Squarehead's Master, Cappelle Desprez and Riband with water or sulphurous acid (pH 4), the ratio of leaves infected by P. nodorum to leaves infected by M. graminicola was increased by factors of 2·5, 2·1 and 0·6, respectively at pH 4. The same three cultivars of wheat were grown in sand and vermiculite and fertilized with nutrient solution containing 2·5 or 0·5 mm sulphate. Both pathogens infected less frequently at 2·5 mm sulphate, by a factor of about 2. The severity of infection by M. graminicola was reduced on all three cultivars by a factor of about 4·5 at 2·5 mm sulphate, but severity of P. nodorum was reduced only by a factor of about 2. Both elevated free sulphate concentrations in soil and sulphite in rainwater could therefore increase the prevalence of P. nodorum relative to M. graminicola, which is consistent with the historical changes in abundance.