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Insight into pathogen population dynamics provides a key input for effective disease management of the potato late blight pathogen Phytophthora infestans. Phytophthora infestans populations vary from genetically complex to more simple with a few clonal lineages. The presence or absence of certain strains of P. infestans may impact the efficacy of fungicides or host resistance. Current evidence indicates that genetically, the Irish populations of P. infestans are relatively simple with a few clonal lineages. In this study, P. infestans populations were genetically characterized based on samples collected at the national centre for potato breeding during the period 2012–16. The dominance of clonal lineages within this P. infestans population was confirmed and the potential selection pressure of fungicide treatment (2013–15) and host resistance (2016) on this clonal P. infestans population was then investigated. It was found that fungicide products did not notably affect the genetic structure of sampled populations relative to samples from untreated control plants. In contrast, samples taken from several resistant potato genotypes were found to be more often of the EU_13_A2 lineage than those taken from control King Edward plants or potato genotypes with low resistance ratings. Resistant potato varieties Sarpo Mira and Bionica, containing characterized R genes, were found to strongly select for EU_13_A2 strains. [ABSTRACT FROM AUTHOR]

Fungal infections of barley have tremendous agricultural significance, and can be detrimental or beneficial. Beneficial root infections often involve endophytic fungi, but endophytic associations do not always confer benefits on their hosts. Endophyte infection can be negative, positive or neutral for the host. Benefits to barley and other plants infected with endophytic root fungi include an increase in seed yield, enhanced resistance to pathogens and improved stress tolerance. Even if an endophyte is never pathogenic, it is not always beneficial. The most important factors that determine the nature of the relationship are the specific combination of partner genotypes and developmental stage, and the ecological and environmental setting. The nutrient status of the plant and the availability of soil nutrients may have little effect on the degree of beneficial endophyte colonization and, unlike mycorrhizae, there is no apparent increase in endophyte-associated phosphorous transfer. There are indications of an association between successful endophyte colonization and high soil pH and clay content. The greatest benefits to the barley plant resulting from the associations seem to be obtained in abiotically stressed environments. Fungal infection may give the plant a greater ability to cope with the stress if the partners are in a balanced relationship. Each new study reveals an increasing diversity of beneficial fungal root endophytes and the full potential of these organisms is still to be determined. Further studies are urgently required to develop specific beneficial root–endophyte associations, or combination of them, that are tailored to individual barley varieties for maximum impact in agriculture. [ABSTRACT FROM PUBLISHER]

The effect of small temperature differentials (16 vs. 20°C) on the pathogenicity of deoxynivalenol producing single isolates ofFusarium culmorumandF. graminearumand on the fusarium head blight (FHB) response of eight wheat cultivars was examined.Fusarium culmoruminoculation caused greater visual disease symptoms at 20°C than at 16°C, both overall and on an individual cultivar basis (overall AUDPC = 13·5 and 9·6, respectively) (P < 0·05). In contrast,F. graminearuminoculation caused greater overall visual disease symptoms at 16°C than at 20°C, both overall and at the individual cultivar level (overall AUDPC = 12·8 and 10·9, respectively) (P < 0·05). Results showed bothF. culmorumandF. graminearuminoculations caused a greater loss in yield at 20°C (54·3 and 46·9% relative 1000-grain weight, respectively) compared with 16°C (73·3 and 66·9% relative 1000-grain weight, respectively) (P < 0·05).Fusarium culmorum-inoculated heads contained similar amounts of fungal DNA at both 16 and 20°C (1·9 and 1·7 ng mg−1 of plant material, respectively) (not significant), while forF. graminearuminoculation, plants contained higher amounts of fungal DNA at 20°C (2·0 and 1·0 ng mg−1 of plant material, respectively) (P < 0·05). Overall, there was a significant negative correlation between AUDPC and percentage relative 1000-grain weight at both 16 and 20°C (r =−0·693 and−0·794, respectively,P < 0·01). [ABSTRACT FROM AUTHOR]

The pathogenic and genetic diversity ofColletotrichum lindemuthianumisolates collected from a total of 10 Central and South American, European and African countries were characterized using common bean differential cultivar pathogenicity tests and amplified fragment length polymorphism (AFLP) analysis. On the basis of pathogenicity tests, 74 isolates were attributed to 30 different pathogenic races using the CIAT-defined binary race-classification system. Twenty-one races were restricted geographically, being exclusive to different countries. Race 9 was the most widespread, being detected in four different countries. Cluster analysis of consensus AFLP data generated using three selective AFLP primer combinations grouped 86 isolates (including the 74 subjected to pathogenicity tests) into three clusters (with one isolate as an outlier). This analysis showed that the majority of South and Central American isolates were divided among two clusters, and that the limited number of European and African isolates used in this study were genetically most similar to Central American isolates. Overall, the results of this research showed some associations between the genetic diversity of the isolates and their country of origin, but not between genetic diversity and race classification of isolates. [ABSTRACT FROM AUTHOR]