Aspects of the biology, epidemiology and control of Rhizoctonia Solani (Kühn) on potato

Aspects of the biology, epidemiology and control of Rhizoctonia solani from potato were investigated using a range of laboratory and field-based experiments. In vitro experiments revealed nutritional factors including a range of carbon sources, and inorganic and organic nitrogen did not affect significantly mycelial growth or sclerotial germination. Carbon and nitrogen sources including cellobiose, glucose, glycerol and potassium nitrate significantly increased sclerotial biomass production in vitro. Mycelial growth, sclerotial production and germination occurred over a temperature range of 10-30oC, with an optimum of 25oC for both AG 2-1 and AG 3 isolates. Mycelial growth and sclerotial germination occurred at pH 4-9 with an optimum of pH 5.6, whereas sclerotial production occurred between pH 4-6 for AG 2-1 isolates and pH 4-8 for AG 3 isolates. Mycelial growth, sclerotial biomass production and germination declined with decreasing osmotic, matric and soil water potential, with mycelial growth prevented between -3.5 MPa and -4.0MPa on osmotically adjusted media, at -2.0 MPa on metrically adjusted media and -6.3 MPa in soil. Sclerotial production ceased prior to the limits for mycelial growth and germination for all isolates, between -1.5 MPa and -3.5 MPa on osmotically adjusted media and -1.5 MPa on metrically adjusted media. AG 3 isolates produced significantly more well-formed sclerotia during all in vitro experiments compared to the loosely constructed sclerotia produced by AG 2-1 isolates. A pathogenicity bioassay, coupled with staining and microscopic examination of stem tissues, showed all AGs formed infection cushions as a prerequisite to infection, with clear differences in the extent of infection cushion formation and subsequent stem lesion severity. AG 2-1 produced small, infrequent infection cushions, causing stem lesions only 1-2 mm in length which did not increase in size or severity after initial formation

Investigation of molecular mechanisms associated with fungicide sensitivity in Irish Pyrenopeziza brassicae populations

© 2020 The Author(s). This an open access work distributed under the terms of the Creative Commons Attribution Licence (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.Light leaf spot is amongst the most damaging diseases of oilseed rape and a significant threat to Irish crops. Unfortunately, the epidemiology of Pyrenopeziza brassicae, the agent causing this disease, remains poorly understood under Irish growing conditions and fungicides are relied upon to provide control. To investigate if the cropping strategies currently used are the best for the control of disease, we screened three populations of P. brassicae isolates from different regions of Ireland for alterations in the genes targeted by azole and Methyl benzamidazole carbamate fungicides. As molecular mechanisms associated with a decrease in fungicide sensitivity were observed in the populations, the results will be correlated with data from fungicide sensitivity tests using these classes of fungicides.Non peer reviewe

Effects of plant age and inoculum concentration on light leaf spot disease phenotypes on oilseed rape

© The Author(s). All rights reserved.Light leaf spot is caused by the fungal pathogen Pyrenopeziza brassicae and is the mosteconomically damaging disease of oilseed rape (Brassica napus) in the UK. Current controlrelies on repeated fungicide applications; however, pathogen fungicide-insensitivitydevelopment highlights the need for non-chemical controls like host resistance. A study wasdone to assess light leaf spot disease phenotype on the susceptible B. napus cultivar Charger indifferent treatment conditions; factors studied included plant age and inoculum concentration.Results showed that older plants grown in a controlled-environment cabinet produced the mostvisible symptoms. Plants that received a greater inoculum concentration (105spores/ml) weresignificantly shorter by 5 cm than those inoculated with a smaller inoculum concentration (104spores/ml), suggesting possible correlations between fungal inoculum concentration and plantgrowth. Additionally, > 20 P. brassicae field isolates were collected from leaf samples acrossEngland through single-spore isolation and will be screened for virulence

Effects of cultivar resistance and fungicide application on stem canker of oilseed rape (Brassica napus) and potential interseasonal transmission of Leptosphaeria spp. inoculum

© 2021 The Authors. Plant Pathology published by John Wiley & Sons Ltd on behalf of British Society for Plant Pathology. This is an open access article under the terms of the Creative Commons Attribution License, https://creativecommons.org/licenses/by/4.0/Phoma stem canker is a damaging disease of oilseed rape (Brassica napus) that causesannual yield losses to UK oilseed rape growers worth approximately £100 million,despite the use of fungicides. In the UK, oilseed rape is sown in August/Septemberand harvested in the following July. The disease epidemics are initiated by ascosporesreleased from Leptosphaeria spp. pseudothecia (ascocarps) on stem stubble in theautumn/winter. Control of this disease is reliant on the use of cultivars with “fieldresistance” and azole fungicides. This study investigated the effects of cultivar resistanceand application of the fungicide prothioconazole on the severity of stem cankerbefore harvest and the subsequent production of pseudothecia on the infected stubbleunder natural conditions in the 2017/2018, 2018/2019, and 2019/2020 croppingseasons. The application of prothioconazole and cultivar resistance decreased theseverity of phoma stem canker before harvest, and the subsequent production ofLeptosphaeria spp. pseudothecia on stubble in terms of pseudothecial density. Resultsshowed that stems with less severe stem cankers produced fewer mature pseudotheciaof Leptosphaeria spp. on the infected stubble. This investigation suggests that themost sustainable and effective integrated control strategy for phoma stem canker inseasons with low quantities of inoculum is to use cultivars with medium or good fieldresistance and apply only one spray of prothioconazole when required.Peer reviewe

Co‐inoculation timing affects the interspecific interactions between phoma stem canker pathogens Leptosphaeria maculans and Leptosphaeria biglobosa

© 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0BACKGROUND: Phoma stem canker is an economically important disease of oilseed rape, caused by two co‐existing fungal pathogen species, Leptosphaeria maculans (Plenodomus lingam) and Leptosphaeria biglobosa (Plenodomus biglobosus). Leptosphaeria maculans produces a phytotoxin called sirodesmin PL. Our previous work showed that L. biglobosa has an antagonistic effect on the production of sirodesmin PL if it is simultaneously co‐inoculated with L. maculans. However, the effects of sequential co‐inoculation on interspecific interactions between the two pathogens are not understood. RESULTS: The interactions between L. maculans and L. biglobosa were investigated in liquid culture by inoculation with L. maculans first, followed by L. biglobosa sequentially at 1, 3, 5 or 7 days later and vice versa; the controls were inoculated with L. maculans only, L. biglobosa only, or L. maculans and L. biglobosa simultaneously. The results showed that L. biglobosa inhibited the growth of L. maculans, the production of both sirodesmin PL and its precursors if L. biglobosa was inoculated before, or simultaneously with, L. maculans. However, the antagonistic effects of L. biglobosa were lost if it was co‐inoculated 5 or 7 days after L. maculans. CONCLUSION: For the first time, the results of this study provided evidence that the timing when L. maculans and L. biglobosa meet significantly influences the outcome of the interspecific competition between them. Leptosphaeria biglobosa can inhibit the production of sirodesmin PL and the growth of L. maculans if it is inoculated before L. maculans or less than 3 days after L. maculans in liquid culture. There is a need to further investigate the timing of co‐inoculation on interactions between L. maculans and L. biglobosa in their host plants for improving the control of phoma stem canker. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.Peer reviewe

Chemical warfare: the fungal quest to conquer oilseed rape

Final Accepted Versio

Leptosphaeria biglobosa inhibits the production of sirodesmin PL by L. maculans

© 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/BACKGROUND: Phoma stem canker is caused by two coexisting pathogens, Leptosphaeria maculans and L. biglobosa. They coexist because of their temporal and spatial separations, which are associated with the differences in timing of their ascospore release. L. maculans produces sirodesmin PL, while L. biglobosa does not. However, their interaction/coexistence in terms of secondary metabolite production is not understood. RESULTS: Secondary metabolites were extracted from liquid cultures, L. maculans only (Lm only), L. biglobosa only (Lb only), L. maculans and L. biglobosa simultaneously (Lm&Lb) or sequentially 7 days later (Lm+Lb). Sirodesmin PL or its precursors were identified in extracts from ‘Lm only’ and ‘Lm+Lb’, but not from ‘Lm&Lb’. Metabolites from ‘Lb only’, ‘Lm&Lb’ or ‘Lm+Lb’ caused significant reductions in L. maculans colony area. However, only the metabolites containing sirodesmin PL caused a significant reduction to L. biglobosa colony area. When oilseed rape cotyledons were inoculated with conidia of ‘Lm only’, ‘Lb only’ or ‘Lm&Lb’, ‘Lm only’ produced large gray lesions, while ‘Lm&Lb’ produced small dark lesions similar to lesions caused by ‘Lb only’. Sirodesmin PL was found only in the plant extracts from ‘Lm only’. These results suggest that L. biglobosa prevents the production of sirodesmin PL and its precursors by L. maculans when they grow simultaneously in vitro or in planta. CONCLUSION: For the first time, L. biglobosa has been shown to inhibit the production of sirodesmin PL by L. maculans when interacting simultaneously with L. maculans either in vitro or in planta. This antagonistic effect of interspecific interaction may affect their coexistence and subsequent disease progression and management.Peer reviewe

Calcium Handling Defects and Cardiac Arrhythmia Syndromes

K

Effects of a penthiopyrad and picoxystrobin fungicide mixtureon phoma stem canker (Leptosphaeria spp.) on UK winteroilseed rape

© Koninklijke Nederlandse Planteziektenkundige Vereniging 2016. This is a pre-copyedited, author-produced PDF of an article accepted for publication in European Journal of Plant Pathology following peer review. The final publication [Sewell, T.R., Moloney, S., Ashworth, M. et al., European Journal of Plant Pathology (2016) 145: 675-685, first published online April 5, 2016] is available at Springer via doi: http://dx.doi.org/10.1007/s10658-016-0916-8In the UK, fungicides are often used to controlphoma stem canker on winter oilseed rape. Field trialswere established near Boxworth, Cambridgeshire for fourcropping seasons (2011/2012, 2012/2013, 2013/2014 and2014/15) to test the efficacy of a new fungicide mixtureRefinzar® (penthiopyrad + picoxystrobin) by comparisonto an existing fungicide Proline 275® (prothioconazole)against phoma stem canker (Leptosphaeria spp.) andthe effect on winter oilseed rape (cv. Catana) yield. Ineach season, weather data were collected from a weatherstation at Boxworth and the release of ascospores wasmonitored using a nearby Burkard spore sampler. Thepatterns of ascospore release differed between seasonsand related to weather conditions. Fungicidespenthiopyrad + picoxystrobin and prothioconazole wereapplied in October/November when 10 % of plants hadphoma leaf spotting (T1, early), 4/8 weeks after T1 (T2,late) or at both T1 and T2 (combined). When phoma leafspot symptoms were assessed in autumn/winter,penthiopyrad + picoxystrobin and prothioconazole bothdecreased numbers of phoma leaf spots caused byL. maculans; there were few leaf spots caused byL. biglobosa. Penthiopyrad + picoxystrobin andprothioconazole both reduced phoma stem canker severitybefore harvest compared to the untreated control butdid not increase yield in these seasons when epidemicswere not severe. In 2013/2014, the presence ofL. maculans and L. biglobosa in upper stem lesions orstem base cankers was determined by species-specificPCR. The proportions of stems with L. maculans DNAwere much greater than those with L. biglobosa DNA forboth upper stem lesions and basal stem cankers. Theseresults suggest that both penthiopyrad + picoxystrobinand prothioconazole can decrease phoma stem cankerseverity on winter oilseed rape in severe disease seasons.Peer reviewe

Effects of different fungicides on the severity of phoma stem canker

Poster abstractPhoma stem canker, a disease of oilseed rape (Brassica napus) caused by sibling pathogens Leptosphaeria maculans and L. biglobosa. Both pathogens follow a monocylic disease cycle that causes leaf spotting in autumn/winter and stem cankers in spring/summer. Most severe cankers decrease transportation of water and nutrients. Fungicides are important for phoma stem canker control. Triazole fungicides currently dominate the market, although reduced sensitivity in some plant pathogen species is a concern. Moreover, L. maculans and L. biglobosa have shown differing level of sensitivity to triazole fungicides. Therefore, increased knowledge on controlling phoma stem canker using non-triazole based fungicides is essential. Field trials were established for 2013/2014 cropping season. Four fungicides were applied: penthiopyrad, picoxystrobin, prothioconazole and a novel fungicide. Spray timings were divided into three sprays T1 (phoma leaf spotting incidence ≥10%), T2 (3/4 weeks post T1) and T3 (Sclerotinia). Phoma leaf spotting incidence and stem canker severity were recorded. In vitro sensitivity testing was done on one L. maculans (ME24) and one L. biglobosa (68) isolate. Prothioconazole showed no noteworthy advantage over the novel fungicide in canker severity scoring. No significant difference in growth inhibition was observed between L. biglobosa and L. maculans (P ≤ 0.05) when treated with novel fungicide. Canker severity indicates that the novel fungicide has a similar efficacy to triazole fungicides. Fungicide sensitivity testing shows that L. biglobosa does not have an increased sensitivity to non-triazole fungicides. This interaction suggests that the novel fungicide could be used to control both L. maculans and L. biglobosaNon peer reviewe