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In the UK, fungicides are often used to control phoma stem canker on winter oilseed rape. Field trials were established near Boxworth, Cambridgeshire for four cropping seasons (2011/2012, 2012/2013, 2013/2014 and 2014/15) to test the efficacy of a new fungicide mixture Refinzar® (penthiopyrad + picoxystrobin) by comparison to an existing fungicide Proline 275® (prothioconazole) against phoma stem canker ( Leptosphaeria spp.) and the effect on winter oilseed rape (cv. Catana) yield. In each season, weather data were collected from a weather station at Boxworth and the release of ascospores was monitored using a nearby Burkard spore sampler. The patterns of ascospore release differed between seasons and related to weather conditions. Fungicides penthiopyrad + picoxystrobin and prothioconazole were applied in October/November when 10 % of plants had phoma leaf spotting (T1, early), 4/8 weeks after T1 (T2, late) or at both T1 and T2 (combined). When phoma leaf spot symptoms were assessed in autumn/winter, penthiopyrad + picoxystrobin and prothioconazole both decreased numbers of phoma leaf spots caused by L. maculans; there were few leaf spots caused by L. biglobosa. Penthiopyrad + picoxystrobin and prothioconazole both reduced phoma stem canker severity before harvest compared to the untreated control but did not increase yield in these seasons when epidemics were not severe. In 2013/2014, the presence of L. maculans and L. biglobosa in upper stem lesions or stem base cankers was determined by species-specific PCR. The proportions of stems with L. maculans DNA were much greater than those with L. biglobosa DNA for both upper stem lesions and basal stem cankers. These results suggest that both penthiopyrad + picoxystrobin and prothioconazole can decrease phoma stem canker severity on winter oilseed rape in severe disease seasons. [ABSTRACT FROM AUTHOR]

Blackleg (Phoma stem canker), caused by the Leptosphaeria species complex L. maculans and L. biglobosa, is a severe and economically important disease in most oilseed production areas worldwide. In this study, the virulence structure of a population of 115 L. maculans isolates from six counties in Alberta, Canada, was determined on three differential canola cultivars, Westar, Quinta and Glacier. Based on the differential interactions as assessed on a 0-9 severity scale, the isolates were classified into four pathogenicity groups: PG-2, PG-T, PG-3, and PG-4. When the differential interactions were assessed by analysis of variance of lesion size, the isolates were classified as into PG-2, PG-T and PG-4, among which PG-4 was predominant comprising 59% of the isolates, followed by PG-T at 37% and PG-2 at 4%. The presence or absence of five avirulence genes, AvrLm1, AvrLm4-7, AvrLm6, AvrLmJ1 and AvrLm11, in each of the isolates was evaluated by PCR analysis. AvrLm1 was absent, while AvrLm4-7 and AvrLm6 were present, in all of the 115 isolates. AvrLmJ1 and AvrLm11 were present in most isolates but absent in three isolates collected from Ponoka County. AvrLm11 also was absent in another two isolates collected from Strathcona County. This study describes the current status of virulence in L. maculans population in Alberta, which may provide guidance for blackleg resistance breeding efforts and cultivar deployment. [ABSTRACT FROM AUTHOR]

Blackleg, caused by the Leptosphaeria maculans/L. biglobosa, is one of the most damaging diseases of Brassica spp. Isolates of L. maculans and L. biglobosa were recovered from oilseed rape, cabbage and broccoli in Lithuania. All isolates from cabbage were identified as L. biglobosa, while both fungal species were detected on broccoli and oilseed rape. Amplified fragment length polymorphism (AFLP) analysis was used to assess the genetic diversity among 68 isolates of L. maculans and L. biglobosa. Cluster analysis divided isolates into two groups of L. maculans and L. biglobosa species. Analysis of molecular variance attributed 57.9% of molecular variance to differences among isolates within the population of L. maculans and 26.6% within the population of L. biglobosa. This is the first study that demonstrates the coexistence of both Leptosphaeria species on B. oleracea in Lithuania. Analysis of molecular variance showed that the populations of Leptosphaeria spp from different host plants were genetically differentiated. [ABSTRACT FROM AUTHOR]

Phoma stem canker (blackleg), caused by the fungi Leptosphaeria maculans and L. biglobosa, is the most devastating disease in oilseed rape (canola) production worldwide. In this study, 84 Leptosphaeria isolates were collected in China from rapeseed ( Brassica napus) plants with blackleg symptoms and identified using multiplex PCR and rDNA-ITS sequence analysis. Results showed that all these isolates are L. biglobosa and no L. maculans was detected. A total of 99 isolates was analyzed, including 15 other L. biglobosa isolates from the UK, Canada and Poland using rDNA-ITS sequences, and all isolates were found to belong to the L. biglobosa 'brassicae' subclade. The genetic variation of these 99 isolates was tested using ISSR (inter simple sequence repeats) markers using 24 polymorphic primers pairs that generated 241 bands by ISSR-PCR amplification. A dendrogram based on weighted pair group mean analysis of these bands revealed that L. biglobosa isolates from China clustered into different groups from those obtained from Canada and Europe. Furthermore, Chinese isolates from seven provinces, except those from Jiangsu, could be placed within the same cluster, based on geographical location. Nei's gene diversity ranged from 0.25 in Jiangsu to 0.11 in Sichuan, and Shannon's information index from 0.16 to 0.37. Genetic identity ranged from 0.784 to 0.834 when isolates from China were compared with those from Canada and the UK, respectively. Analysis of gene flow among populations (Nm) indicated that almost no gene exchange has occurred between L. biglobosa in China and the populations of the fungus from the UK or Canada. [ABSTRACT FROM AUTHOR]

A combination of staining, light microscopy and SYBR green- and dual-labelled fluorescent probe-based qPCR chemistries with species- and gene-specific primers was employed to evaluate fluctuations in the aerial biomass of Leptosphaeria maculans spores captured by volumetric spore trappings in Poznan, Poland (2006, 2008) and Harpenden, UK (2002, 2006). Arising from these surveys, DNA samples extracted from Burkard spore-trap tapes were screened for fluctuation patterns in the frequencies of AvrLm1 and AvrLm6, the most prominent of the 15 genes that code for avirulence effectors in this Dothideomycete cause of the destructive phoma stem canker disease of oilseed rape worldwide. In Poznan, very low frequencies of AvrLm1 allele were found in the autumn of both 2006 and 2008, reflecting significantly increased cultivation of rape seed with Rlm1-based resistance. In contrast, at least six folds-higher frequencies of AvrLm6, which were also confirmed by end-point PCR bioassays on phoma-infected leaves from the same region of Poland, were obtained during both years. In the UK, however, relatively higher AvrLm1 allele titres were found in L. maculans spores captured in air samples from the autumn of 2002 on the experimental fields of Rothamsted Research, Harpenden, that were historically sown to genetically heterogeneous B. napus cultivars. In the 2006 screen these levels had plummeted, to a 1:4 ratio, in favour of frequencies of the AvrLm6 allele. Patterns of fluctuations in erg11 ( CYP51) fragments coding for sterol 14α-demethylase suggest October as the month with the most viable wind-dispersed L. maculans propagules of each season of the screens. [ABSTRACT FROM AUTHOR]

Weather data generated for different parts of the UK under five climate change scenarios (baseline, 2020s low CO2 emissions, 2020s high emissions, 2050s low emissions, 2050s high emissions) were inputted into weather-based models for predicting oilseed rape yields and yield losses from the two most important diseases, phoma stem canker and light leaf spot. An economic analysis of the predictions made by the models was done to provide a basis to guide government and industry planning for adaptation to effects of climate change on crops to ensure future food security. Modelling predicted that yields of fungicide-treated oilseed rape would increase by the 2020s and continue to increase by the 2050s, particularly in Scotland and northern England. If stem canker and light leaf spot were effectively controlled, the value of the crop was predicted to increase above the baseline 1980s value by £13 M in England and £28 M in Scotland by the 2050s under a high CO2 emissions scenario. However, in contrast to predictions that phoma stem canker will increase in severity and range with climate change, modelling indicated that losses due to light leaf spot will decrease in both Scotland and England. Combined losses from both phoma stem canker and light leaf spot are predicted to increase, with yield losses of up to 40% in southern England and some regions of Scotland by the 2050s under the high emission scenarios. For this scenario, UK disease losses are predicted to increase by £50 M (by comparison with the baseline losses). However, the predicted increases in fungicide-treated (potential) yield and phoma stem canker/light leaf spot yield losses compensate for each other so that the net UK losses from climate change for untreated oilseed rape are small. [ABSTRACT FROM AUTHOR]