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Neonectria ditissima infects apple trees through wounds, causing European canker. In the UK, the most important entry site for N. ditissima is leaf scar. Specific apple endophytes may contribute to cultivar resistance/tolerance to the pathogen. We assessed the relative effect of location, sampling time (season), and rootstock/scion genotype on bacterial and fungal endophyte communities in the apple leaf scar tissues of current‐season extension shoots and identified Operational Taxonomic Units (OTUs) with differential abundance between canker resistant and susceptible scions, and between rootstocks. Leaf scar tissues were sampled from two orchards at three times (10/2018, 06/2019 and 10/2019) for eight scion cultivars, each grafted onto two rootstocks, for profiling 16S and ITS rRNA regions. Endophyte composition was primarily affected by season (autumn vs. spring) and location (sites and blocks within site). There was a significant reduction in the community size in the spring, particularly for fungi, and species turnover between autumn and spring. This seasonal dynamics suggest that to protect leaf scars from N. ditissima infection in the autumn specific endophytes suppressing canker may have to be augmented annually around the leaf‐fall time. Scion and rootstock genotypes had limited effects on the endophyte community. A group of resistant cultivars differed from a group of susceptible ones in the relative abundance of many bacterial and fungal OTUs, most of which had low reads numbers. Nevertheless, several OTUs with high reads numbers differed in their relative abundance between resistant and susceptible scions, including OTUs from Sphingomonas, Methylobacterium, Vishniacozyma and Rhodotorula babjevae, and warrant further investigation for their potential role in host resistance/tolerance against N. ditissima. [ABSTRACT FROM AUTHOR]

There is little information on the effect of temperature, relative humidity (RH) and vapour pressure deficit (VPD) on the viable populations of two commercial biocontrol strains, Bacillus subtilis QST 713 (recently classified as B. velezensis) and Gliocladium catenulatum J1446 (syn. Clonostachys rosea). The PMAxx‐qPCR molecular assay was used to quantify the viable biocontrol agent (BCA) populations on fully extended lettuce and strawberry leaves under a range of temperature and RH combinations. Overall, there was a small decline in the population size of viable cells for the two biocontrol organisms on strawberry and lettuce leaves within 10 days of application. However, for most experimental runs, which contained general UK agronomy climates, such a decline was not statistically significant. Moreover, for a few runs, the viable populations increased significantly in optimal BCA growth temperatures with high RH. Only temperature (ambient) and dew point significantly affected the rate of temporal changes in the viable biocontrol population size. Thus, an increasing temperature led to decreased daily mortality. It should be noted that much of the variability in the estimated daily mortality rates remains unaccounted for, thus unless under extreme conditions, the biocontrol efficacy in practice is less likely to be affected by the survival of biocontrol microbes but more likely by other factors that influence the density of biocontrol cells in the phyllosphere, especially dilution due to rapid host leaf expansion, spray coverage and rain wash‐off. [ABSTRACT FROM AUTHOR]

Apple rootstock genotypes confer different levels of tolerance to apple replant disease (ARD) and vigour to a newly replanted apple tree. A hybrid management system of rotating the rootstock genotype planted between successive generations and inter-row planting in the alleyways of orchards may minimise the severity of ARD symptoms. High-throughput sequencing of the fungal ITS and bacterial 16S rDNA regions was used to investigate the diversity, and differential taxa present in soils displaying symptoms of ARD. Candidate pathogens and beneficial microorganisms were correlated with the above-ground establishment of each rootstock genotype in a UK cider orchard. Our results suggest that the same rootstock or rootstock with closely related parentage to the previous rootstock had more severe ARD symptoms. Planting in the alleyway appeared an effective strategy to minimise the severity of symptoms irrespective of rootstock genotype. The planting location effect had a higher contribution to the variation in the rhizosphere microbiome than that of the rootstock genotype. No predicted causal agents for ARD could be identified to a taxonomic level to predict their function but two species associated with mycorrhizae, Pteridiospora spinosispora and Paraglomus laccatum were identified as inversely correlated with ARD severity and could be candidate beneficial species for apple, warranting further investigation and research. Our findings suggest that planting in the alleyways and planting rootstocks genetically dissimilar to the previously planted rootstock can be beneficial for tree establishment. We have also identified species inversely associated with ARD severity, making candidates for future research to test the antagonistic effect of the species against ARD pathogens in apple roots. [ABSTRACT FROM AUTHOR]

Raspberry (Rosales: Rosaceae) production in the U.K. has moved rapidly in the last 10 years to under polythene, combined with a reduced availability of broad-spectrum fungicides. Hence, the incidence of previously less prevalent diseases, such as Cladosporium (Capnodiales: Cladosporiaceae), has largely increased. This study aimed to identify the predominant Cladosporium species on raspberry and to understand the nature of its infection on raspberry fruit. Raspberries were collected from farms across the U.K. and Spain and incubated; fungal isolates were then isolated from typical Cladosporium lesions and identified to the species level based on the sequences of the trans elongation factor α and actin genes. Cladosporium cladosporioides (Fres) de Vries was confirmed as the predominant species responsible for infecting raspberry fruit close to harvest on fruit from the U.K. and Spain, being present on 41.5% of U.K. fruit and 84.6% of Spanish fruit. Raspberries were subsequently inoculated at different developmental stages with C. cladosporioides isolates to determine the susceptibility to Cladosporium skin lesions and stigmata infections in relation to the developmental stage. Only the ripening and ripe raspberries were susceptible to Cladosporium, resulting in skin lesions. Cladosporium can colonise the stigmata of raspberries earlier in fruit development and future research is required to determine if such stigmata infections could cause subsequent skin lesion infections. This study has provided the necessary epidemiological information to develop effective management measures against the Cladosporium species. [ABSTRACT FROM AUTHOR]

Powdery mildew, caused by Podosphaera aphanis, is an important disease of strawberries under protection. Botrytis fruit rot is an important cause of losses in strawberries particularly under open-field conditions. Current control of both these diseases in the UK is dependent on conventional fungicides. Recently, research in the UK demonstrated that integrating biopesticides and biostimulants with a decision-based management programme could achieve reductions in conventional fungicide use without loss in yield or fruit quality. Further field studies were conducted to extend the decision-based management programme to include control of Botrytis fruit rot on everbearer crops. In 2018, three management programmes were compared to a routine fungicide-based programme and an untreated control. In two management programmes, treatments for Botrytis and powdery mildew were either applied routinely or managed. In the third programme, treatments for both diseases were managed. Disease risks were estimated with a simple lookup table based on past and forecast weather. The results showed that the integrated management for both diseases resulted in a nearly 45% reduction in conventional fungicide use and a cost saving of £699/ha compared to a routine programme with no penalties in yield, fruit quality or disease control. There were no significant effects of treatments on Botrytis rot incidence compared to the untreated control, suggesting that the fungicides applied for controlling Botrytis gave no benefit. In 2019, two treatments based on the decision-based management system for powdery mildew and Botrytis , one of which excluded specific fungicide treatment for Botrytis , were compared to an untreated control and a routine fungicide programme. Cool chain management of the fruit post-harvest was also included to extend post-harvest fruit shelf life. The results showed that the simple decision-based system for determining treatments for mildew and Botrytis based on biopesticides and omitting Botrytis -specific fungicides resulted in a 93% reduction in fungicide use and a cost saving of £924/ha compared to a routine programme with no penalties in yield, fruit quality or disease control. Cool chain management delayed the development of both Botrytis and soft rots. In both years, detectable fungicide residues were considerably reduced in the fruit from the managed programmes. [Display omitted] [ABSTRACT FROM AUTHOR]

We developed a stochastic simulation model incorporating most processes likely to be important in the spread of Phytophthora ramorum and similar diseases across the British landscape (covering Rhododendron ponticum in woodland and nurseries, and Vaccinium myrtillus in heathland). The simulation allows for movements of diseased plants within a realistically modelled trade network and long-distance natural dispersal. A series of simulation experiments were run with the model, representing an experiment varying the epidemic pressure and linkage between natural vegetation and horticultural trade, with or without disease spread in commercial trade, and with or without inspections-with-eradication, to give a 2×2×2×2 factorial started at 10 arbitrary locations spread across England. Fifty replicate simulations were made at each set of parameter values. Individual epidemics varied dramatically in size due to stochastic effects throughout the model. Across a range of epidemic pressures, the size of the epidemic was 5–13 times larger when commercial movement of plants was included. A key unknown factor in the system is the area of susceptible habitat outside the nursery system. Inspections, with a probability of detection and efficiency of infected-plant removal of 80% and made at 90-day intervals, reduced the size of epidemics by about 60% across the three sectors with a density of 1% susceptible plants in broadleaf woodland and heathland. Reducing this density to 0.1% largely isolated the trade network, so that inspections reduced the final epidemic size by over 90%, and most epidemics ended without escape into nature. Even in this case, however, major wild epidemics developed in a few percent of cases. Provided the number of new introductions remains low, the current inspection policy will control most epidemics. However, as the rate of introduction increases, it can overwhelm any reasonable inspection regime, largely due to spread prior to detection. [Copyright &y& Elsevier]

Powdery mildew, caused by Podosphaera aphanis, is an important disease of strawberries and currently its control in the UK is very dependent on conventional fungicides. A series of experiments were carried out to integrate conventional fungicides with biopesticides and biostimulants for mildew control. In 2015–2016, the biopesticides Sonata (Bacillus pumilis) and AQ10 (Ampelomyces quisqualis) achieved at least as good as or better mildew control where they were applied alone rather than alternated with or tanked mixed with conventional fungicides. Three mildew management programmes were evaluated in 2017 on an ever-bearer cultivar. In the B. pumilis based programme, the need for treatment and the choice of products were partially determined by predicted mildew risks. The incidence of mildew on leaves was very low in untreated plots with virtually no mildew observed in the other treated plots. By contrast, mildew on the fruit rose rapidly from 2 % in late July to >90 % in late August in untreated plots. In treated plots, the percentage of fruit with mildew did not rise above 3 % with the three managed programmes based on B. pumilis. There were no significant differences in total yield and marketable yield between the managed programmes and the routine fungicide programme, but all were significantly greater than the untreated control. Most of the unmarketable fruit in the untreated control was due to infection with powdery mildew. The results suggested that strawberry powdery mildew can be effectively managed by the integrated use of biopesticides, biostimulants and conventional fungicides. [Display omitted] [ABSTRACT FROM AUTHOR]