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Stem canker of brassicas, also known as blackleg is the most damaging disease of many Brassicaceae. The disease is caused by Leptosphaeria maculans (Desm.) Ces et de Not. and L. biglobosa sp. nov., Shoemaker & Brun, which coexist in plants and resulting in disease symptoms and decreased yield, quantity and quality of cultivated vegetables and oilseed rape. The paper presents taxonomic relationships between these coexisting pathogen species, describes particular stages of their life cycles, summarizes the differences between the species, and reviews methods for their identification.
Potato white mold caused by Sclerotinia sclerotiorum is an important plant disease occurring in many potato-producing areas throughout the world. In this study, a specific diagnostic method was used to detect and quantify S. sclerotiorum ascospores, and its forecasting ability was assessed in potato fields during flowering periods of 2011 to 2014 in Bahar County, Hamedan Province. Using GenEMBL database, a primer pair, HZSCREV and HZSCFOR, was designed and optimized for the pathogen. After testing the sensitivity of primers, DNA was extracted from samples of outdoor Burkard traps from potato fields. A linear association was observed between pathogen DNA and the number of ascospores using the quantitative PCR (qPCR) technique in the presence of SYBR dye. The qPCR could successfully detect DNA amounts representing two S. sclerotiorum ascospores and was not sensitive to a variety of tested fungi such as Botrytis cinerea, Alternaria brassicae, Fusarium solani. In contrast to the amount of rainfall, a direct relationship was found between ascospore numbers and the incidence of potato white mold from 2011 to 2014.
Spores of many fungal pathogens are dispersed by wind. Detection of these airborne inocula is important in forecasting both the onset and the risk of epiphytotics. Species-specific primers targeted at the internal transcribed spacer (ITS) region of Leptosphaeria maculans and L. biglobosa - the causal organisms of phoma stem canker and stem lesions of Brassica spp., including oilseed rape - were used to detect DNA extracted from particles deposited on tapes obtained from a spore trap operated in Rarwino (northwest Poland) from September to November in 2004 and 2006. The quantities of DNA assessed by traditional end-point PCR and quantitative real-time PCR were compared to microscopic counts of airborne ascospores. Results of this study showed that fluctuations in timing of ascospore release corresponded to the dynamics of combined concentrations of DNA from L. maculans and L. biglobosa, with significant positive correlations between ascospore number and DNA yield. Thus the utilization of PCR-based molecular diagnostic techniques enabled the detection, identification, and accurate quantification of airborne inoculum at the species level. Moreover, real-time PCR was more sensitive than traditional PCR, especially in years with low ascospore numbers.
The effect of pre-leaf fan of 5% urea treatment on primary infection of apple by Venturia inaequalis, the cause of scab, was investigated in commercial apple orchards of McIntosh cv. in different region s of Poland, at Miłobądz, Sinołęka and Dąbrowice. Additionally, the development of pseudothecia and maturation of ascospores were evaluated in the spńng on apple leaves of two cultivars (McIntosh and Gloster) treated with 5% solution of urea. Microscopic observations of leaves showed that urea treatment significantly reduced the number of pseudothecia (by ca. 90%) and ascospore production. Low number of ascospores after urea treatment has strongly affected primary infection of apple by the fungus in all tested orchards. Reduction of leaf infection on control trees was usually more than 30%. Also efficacy of chemical control of apple scab was significantly higher on plots treated with urea.
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