The Rhynchosporium species complex consists of hemibiotrophic fungal pathogens specialized to different sweet grass species including the cereal crops barley and rye. A sexual stage has not been described, but several lines of evidence suggest the occurrence of sexual reproduction. Therefore, a comparative genomics approach was carried out to disclose the evolutionary relationship of the species and to identify genes demonstrating the potential for a sexual cycle. Furthermore, due to the evolutionary very young age of the five species currently known, this genus appears to be well-suited to address the question at the molecular level of how pathogenic fungi adapt to their hosts. The genomes of the different Rhynchosporium species were sequenced, assembled and annotated using ab initio gene predictors trained on several fungal genomes as well as on Rhynchosporium expressed sequence tags. Structures of the rDNA regions and genome-wide single nucleotide polymorphisms provided a hypothesis for intra-genus evolution. Homology screening detected core meiotic genes along with most genes crucial for sexual recombination in ascomycete fungi. In addition, a large number of cell wall-degrading enzymes that is characteristic for hemibiotrophic and necrotrophic fungi infecting monocotyledonous hosts were found. Furthermore, the Rhynchosporium genomes carry a repertoire of genes coding for polyketide synthases and non-ribosomal peptide synthetases. Several of these genes are missing from the genome of the closest sequenced relative, the poplar pathogen Marssonina brunnea, and are possibly involved in adaptation to the grass hosts. Most importantly, six species-specific genes coding for protein effectors were identified in R. commune. Their deletion yielded mutants that grew more vigorously in planta than the wild type. Both cryptic sexuality and secondary metabolites may have contributed to host adaptation. Most importantly, however, the growth-retarding activity of the species-specific effectors suggests that host adaptation of R. commune aims at extending the biotrophic stage at the expense of the necrotrophic stage of pathogenesis. Like other apoplastic fungi Rhynchosporium colonizes the intercellular matrix of host leaves relatively slowly without causing symptoms, reminiscent of the development of endophytic fungi. Rhynchosporium may therefore become an object for studying the mutualism-parasitism transition.

Many pathogens are dispersed by airborne spores, which can vary in space and time. We can use air sampling integrated with suitable diagnostic methods to give a rapid warning of inoculum presence to improve the timing of control options, such as fungicides. Air sampling can also be used to monitor changes in genetic traits of pathogen populations such as the race structure or frequency of fungicide resistance. Although some image-analysis methods are possible to identify spores, in many cases, species-specific identification can only be achieved by DNA-based methods such as qPCR and LAMP and in some cases by antibody-based methods (lateral flow devices) and biomarker-based methods (‘electronic noses’ and electro-chemical biosensors). Many of these methods also offer the prospect of rapid on-site detection to direct disease control decisions. Thresholds of spore concentrations that correspond to a disease risk depend on the sampler (spore-trap) location (whether just above the crop canopy, on a UAV or drone, or on a tall building) and also need to be considered with weather-based infection models. Where disease control by spore detection is not possible, some diseases can be detected at early stages using optical sensing methods, especially chlorophyll fluorescence. In the case of Fusarium infections on wheat, it is possible to map locations of severe infections, using optical sensing methods, to segregate harvesting of severely affected areas of fields to avoid toxins entering the food chain. This is most useful where variable crop growth or microclimates within fields generate spatially variable infection, i.e. parts of fields that develop disease, while other areas have escaped infection and do not develop any disease.

Sugar beet rust disease (causal agent Uromyces betae) represents a serious threat to worldwide sugar beet (Beta vulgaris) crops, causing yield losses of up to 10% in the United Kingdom. Currently, the disease is managed mainly by application of fungicides after rust disease symptoms appear. Development of a future forecasting system, incorporating data on environmental factors and U. betae inoculum levels, would enable better disease control by more targeted application of fungicides. In this study, we developed a first molecular diagnostic, targeted to cytochrome b DNA sequences and based on loop-mediated isothermal amplification (LAMP) technology, for rapid (<30 min) and specific detection of U. betae. The new assay only detected U. betae strains (collected from across eastern England, the main sugar beet growing region in the United Kingdom) and Denmark; it did not detect other closely related pathogens (e.g., Puccinia sp., U. fabae) or others that are commonly found on sugar beet (Cercospora beticola, Erysiphe betae, Ramularia beticola). The assay could consistently detect down to small amounts of U. betae DNA (10 pg). Application of the new LAMP diagnostic to air spore tape samples collected between mid-June and mid-September from a single U.K. sugar beet field site revealed differences in temporal patterns of pathogen inoculum between the 2015 and 2016 seasons. The described LAMP assay could now be used as a component of a future automated inoculum-based forecasting system, enabling more targeted control of sugar beet rust disease.

Ash (Fraxinus excelsior L.) planted at six sites over the past 20 years was investigated. Three geographically isolated sites (Northumberland, Leicestershire and Devon) were compared with three sites in established areas of ash dieback in East Anglia, and the causal pathogen, Hymenoscyphus fraxineus, confirmed at all. Dieback severity, the frequency of stem basal lesions and pathogen apothecia, were quantified at all sites but despite high disease levels, tree mortality was low. Some trees had typical H. fraxineus stem cankers but had apparently died between 2001 and 2011, before the earliest UK records of H. fraxineus. Ring counts established beyond doubt the year of death and canker initiation in 27 dead trees. Cankers on the same trees were then tested for H. fraxineus using PCR-based detection, with pathogen presence confirmed as early as 2004/05 in some. This places H. fraxineus in England much earlier than previously thought, even pre-dating its documented arrival in neighbouring European countries. The advanced disease levels at some sites plus confirmation of H. fraxineus in old stem cankers, suggests that planting of infected H. fraxineus tree stock in England could date back to the early 1990s, with affected trees dying in the mid-2000s. Additionally, it raises questions about the origins of the infected plants and uncertainties about plant trade pathways.

The fungal genus Rhynchosporium (causative agent of leaf blotch) contains several host-specialised species, including R. commune (colonising barley and brome-grass), R. agropyri (couch-grass), R. secalis (rye and triticale) and the more distantly related R. orthosporum (cocksfoot). This study used molecular fingerprinting, multilocus DNA sequence data, conidial morphology, host range tests and scanning electron microscopy to investigate the relationship between Rhynchosporium species on ryegrasses, both economically important forage grasses and common wild grasses in many cereal growing areas, and other plant species. Two different types of Rhynchosporium were found on ryegrasses in the UK. Firstly, there were isolates of R. commune that were pathogenic to both barley and Italian ryegrass. Secondly, there were isolates of a new species, here named R. lolii, that were pathogenic only to ryegrass species. R. lolii was most closely related to R. orthosporum, but exhibited clear molecular, morphological and host range differences. The species was estimated to have diverged from R. orthosporum ca. 5735 years before the present. The colonisation strategy of all of the different Rhynchosporium species involved extensive hyphal growth in the sub-cuticular regions of the leaves. Finally, new species-specific PCR diagnostic tests were developed that could distinguish between these five closely related Rhynchosporium species.

Light leaf spot, caused by the ascomycete Pyrenopeziza brassicae , is an established disease of Brassicaceae in the United Kingdom (UK), continental Europe, and Oceania (OC, including New Zealand and Australia). The disease was reported in North America (NA) for the first time in 2014 on Brassica spp. in the Willamette Valley of western Oregon, followed by detection in Brassica juncea cover crops and on Brassica rapa weeds in northwestern Washington in 2016. Preliminary DNA sequence data and field observations suggest that isolates of the pathogen present in NA might be distinct from those in the UK, continental Europe, and OC. Comparisons of isolates from these regions using genetic (multilocus sequence analysis, MAT gene sequences, and rep‐PCR DNA fingerprinting), pathogenic ( B. rapa inoculation studies), biological (sexual compatibility), and morphological (colony and conidial morphology) analyses demonstrated two genetically distinct evolutionary lineages. Lineage 1 comprised isolates from the UK, continental Europe, and OC, and included the P. brassicae type specimen. Lineage 2 contained the NA isolates associated with recent disease outbreaks in the Pacific Northwest region of the USA. Symptoms caused by isolates of the two lineages on B. rapa and B. juncea differed, and therefore “chlorotic leaf spot” is proposed for the disease caused by Lineage 2 isolates of P. brassicae . Isolates of the two lineages differed in genetic diversity as well as sensitivity to the fungicides carbendazim and prothioconazole.