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Zymoseptoria tritici is the causal fungus of Septoria tritici blotch (STB), a globally important foliar disease of wheat. Infections by more than one strain of a pathogen, or co‐infections, are known to be the most prevalent form of infection in the field. The impact that co‐infection of Z. tritici has on disease severity for the plant host and its effect on plant defence are not fully understood. Here, isolates of Z. tritici were extracted from STB‐presenting leaves from UK sites. Disease assays comparing single‐isolate inocula to mixed inocula were carried out on three cultivars of wheat, Flame, Stigg and Longbow. Leaves infected with mixed inocula were found to show low disease symptoms, including lesion and pycnidial coverage, compared with those infected with single isolates. Growing mixed isolates together in liquid media did not reveal evidence of competition or decreased growth compared with single‐isolate inocula. Wheat infected with a mixture of at least two Z. tritici isolates (of differing aggressiveness) could induce Pr‐1 (Pathogenesis‐related 1) at a significantly higher level in distal uninfected leaves compared with distal leaves of plants infected with a single aggressive isolate. Expression of Pr‐1 in plants with mixed inocula was intermediate to plants infected with an aggressive isolate (lower expression) and plants infected with a less aggressive isolate (higher expression). This suggests that wheat undergoes systemic "sensitization" by the least aggressive Z. tritici isolate during co‐infection. [ABSTRACT FROM AUTHOR]

Earlier studies have shown that primary infections of winter wheat crops by septoria tritici blotch are initiated in autumn by air-borne ascospores of the teleomorph stage, Mycosphaerella graminicola, which originate from sources outside the crop. Subsequent disease development within the crop, and damage to the upper leaves in summer, were commonly ascribed to the anamorph stage, Septoria tritici, which first arises from primary, ascosporic lesions and develops to give rise to splash-borne pycnidiospores produced in pycnidia. Trapping studies, using a Burkard volumetric trap sited adjacent to field trials of winter wheat, showed that ascospores are released from pseudothecia throughout the year; peak release is not restricted to the autumn and early winter when the primary infections occur. As M. graminicola ascospores can be confused with those of other species, their authenticity was established by incubating ascospores on trap tapes for 24–48 h before counting. Examination of wheat plants cv. Riband, removed from unsprayed crops just prior to harvest and exposed to external weather conditions over the winter in 1995 and 1996, showed that pseudothecia mature on residues of the upper leaf layers between August and March. However, peak development occurred in December/January, when there was a corresponding decline in pycnidial formation. On regenerated wheat in set-aside (left uncultivated) fields, sources of pseudothecia of M. graminicola were exhausted by February of the following year. Natural development of the teleomorph stage was monitored in an unsprayed crop of winter wheat cv. Riband during the 1996–97 season, and was present on leaf 8 at growth stage 32 (24 April) and on leaf 3 at growth stage 85 (8 July), then a week later, on both leaf 2 and the flag leaf. The temporal development of M. graminicola asexual and sexual phases was also studied in inoculation experiments under external weather conditions on pot-grown seedlings of winter... [ABSTRACT FROM AUTHOR]

Epidemics of disease caused by Septoria tritici were studied in detail in 11 crops of winter wheat cv. Longbow over 4 years. Serious damage to the uppermost two leaf layers was caused by splash-borne infection from lower in the crop early in the life of the leaves, followed by one or rarely two cycles of multiplication within a leaf layer. Infection conditions rarely limited damage, even in a dry year; the timing and, to a lesser extent, amount of initial inoculum movement to an upper leaf layer was of greater importance. Timing of initial infection was determined by when rain splash occurred in relation to emergence of a leaf layer. Occurrence of infections soon after a leaf layer started to emerge allowed more time for multiplication of disease within that layer. These infections tended to be more severe because the leaves were closer to inoculum sources within the crop. Slight differences in phenology between locations explain why initially random disease distributions sometimes become aggregated. Early-sown crops are at greater risk because they mature more slowly, allowing more disease multiplication and better transfer between leaf layers. [ABSTRACT FROM AUTHOR]

Two isolates of Pseudomonas fluorescens (2–79 and 13–79) from the USA were evaluated in the UK as biological control agents against Gaeumannomyces graminis var. tritici, the cause of take-all in wheat. Biological control agents were applied as seed coatings in carboxymethyl cellulose (CMC) to seven wheat trials sown in 1987 and 1988 on ten peat and clay soils, and as peat-based and microgranule formulations in one of these trials. In a trial of spring wheat on fen peat, all treatments with biological control agents reduced the percentage take-all infection of crown roots and seminal roots, but the effects of only one isolate were statistically significant (P< 0.05). Effects of biological control agents on infection rates in five other trials were not significant. In the trial in which application methods were compared, peat-based inoculum initially appeared most effective but none of the treatments reduced take-all significantly throughout the season. Application of biological control agents was associated with yield increases in several trials; these were not consistently associated with effects on take-all. These results suggest that the isolates of P. fluorescens have potential to reduce take-all and increase yields of wheal in the UK, but the beneficial effects are inconsistent. There is a need to develop isolates which reliably control severe take-all in a variety of soil types. [ABSTRACT FROM AUTHOR]

Wheat bunt (Tilietia caries) has previously been controlled in the UK by routine seed treatment with organomercury. Recent examples are presented of unusual levels of infection due to soil-borne inoculum. The recent infections may be due to unusually dry weather, favouring the survival of spores in the soil, or to the presence of a more persistent strain of T. caries. [ABSTRACT FROM AUTHOR]