A qPCR-based method for the detection and quantification of the peach powdery mildew ( Podosphaera pannosa ) in epidemio
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A qPCR-based method for the detection and quantification of the peach powdery mildew (Podosphaera pannosa) in epidemiological studies Neus Marimon & Iban Eduardo & Maela León & Mónica Berbegal & Josep Armengol & Jordi Luque
Received: 18 March 2020 / Revised: 15 September 2020 / Accepted: 11 October 2020 # Koninklijke Nederlandse Planteziektenkundige Vereniging 2020
Abstract A qPCR-based method was developed to detect and quantify Podosphaera pannosa, the main causal agent of peach powdery mildew. A primer pair was designed to target part of the ITS region of the fungal ribosomal DNA, which proved to be highly specific and sensitive. A minimum of 2.81 pg µL− 1 of P. pannosa DNA and 6 conidia mL− 1 in artificiallyprepared conidia suspensions were found to be the limit of detection. Moreover, a quantification of conidia placed on plastic tapes commonly used in volumetric air samplers was performed. Regression equations on conidia quantification obtained either from aqueous conidia suspensions or conidia placed on plastic tapes were similar. The protocol was further validated in field conditions by estimating the number of P. pannosa conidia obtained with an air sampler, by both microscopic and molecular quantification. Both techniques detected the peaks of conidia production during a 4month sampling period, and a significant correlation (r = 0.772) was observed between both quantification methods. Additionally, the molecular method was N. Marimon : J. Luque (*) Plant Pathology, IRTA Cabrils, Carretera de Cabrils km 2, 08348 Cabrils, Spain e-mail: [email protected] N. Marimon : I. Eduardo Centre de Recerca en Agrigenòmica (CRAG), CSIC-IRTA-UAB-UB, UAB Campus, 08193 Bellaterra, Spain M. León : M. Berbegal : J. Armengol Instituto Agroforestal Mediterráneo, Universitat Politècnica de València, Camino de Vera s/n, 46022 València, Spain
applied to detect latent fungal inoculum in different plant parts of peach trees. The pathogen was detected mainly on the bark of affected twigs, and to a lesser extent, in foliar buds. The method developed here can be applied in the study of P. pannosa epidemiology and can help in improving the management of this pathogen through its early detection and quantification. Keywords Aerobiology . Epidemiology . Molecular technique . Powdery mildew . Prunus persica
Introduction The ascomycete Podosphaera pannosa (Wallr.) de Bary is one of the causal agents of powdery mildew that occurs on the Prunus and Rosa genera of Rosaceae (Farr and Rossman 2019; Takamatsu et al. 2010). Other powdery mildew species are rarely found on peach, such as P. clandestina, P. leucotricha, and P. tridactyla (Farr and Rossman 2019). However, P. pannosa is widely recognized as the main causal agent of the peach powdery mildew (PPM). Podosphaera species infect green parts of the tree, e.g. fruits, leaves, buds, and twigs (Grove 1995; Ogawa and English 1991), where a distinguishable white-greyish mycelium develops on the surface of the affected part. Severe infections of P. pannosa on fruit make them unacceptable t
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