First Report of Pseudoperonospora cubensis on Cucurbita moschata in the Czech Republic

Abstract

Pseudoperonospora cubensis (Berk. & M.A. Curtis) Rostovzev, the causal agent of cucurbit downy mildew, was observed for the first time on Cucurbita moschata Duchesne in the Czech Republic (CR) in August 2009 and repeatedly in September 2010. Recently, C. moschata has not been an economically important crop in the CR; however, related crops C. pepo and C. maxima have increased in importance. Infected plants with P. cubensis were found in two locations: in a hobby garden in north Moravia (Nový Jičín – Kojetín [49°33′48.088″N, 17°59′16.632″E], 2009 and 2010) and in a commercial field in central Moravia (Olomouc-Holice [49°34′31.95″N, 17°17′35.462″E], 2010). The pathogen caused small, angular, yellowish or pale green lesions on the upper leaf surfaces and produced sporangiophores and sporangia on the lower leaf surfaces. The lesions were delimited by leaf veins and later turned necrotic. Sporangiophores were hyaline, branched, and emerged in groups from stomata. Olive brown-to-dark brown sporangia were ellipsoidal to oblong. Our morphological observations confirmed that the pathogen was P. cubensis (2). No previous reports are available of P. cubensis on C. moschata in CR or anywhere in Central Europe. However, P. cubensis is common on C. moschata in some parts of Asia and the United States (1,2). P. cubensis exhibiting clear host specialization has been reported in different countries and geographic areas (2). A C. moschata isolate (PC 88/2009) originating from the naturally infected plants was inoculated (1 × 105 spores per ml and incubation temperature of 18/15°C during light/dark cycles) according to the methodology described by Lebeda and Urban (3) onto the abaxial surface of leaf discs of all genotypes of a differential set of cucurbits for P. cubensis pathotype determination (4). C. moschata (line Novo5, Nohel-Garden, CR) was added to this set. The isolate PC 88/2009 was highly pathogenic to all screened Cucurbita spp. genotypes (C. pepo, C. maxima, and C. moschata). However, no infection was detected on most of the Cucumis accessions; only Cucumis melo subsp. agrestis var. conomon was susceptible. Also, no infection was observed on other differentials (Citrullus, Benincasa, Luffa, and Lagenaria). The pathotype was classified as Pc 4/15/0. This pathotype had not been previously detected in CR. References: (1) D. F. Farr and A. Y. Rossman. Fungal Databases. Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved from http://nt.arsgrin. gov/fungaldatabases/ . December 16, 2010. (2) A. Lebeda and Y. Cohen. Eur. J. Plant Pathol. 129:157, 2011. (3) A. Lebeda and J. Urban. Page 285 in: Mass Screening Techniques for Selecting Crops Resistant to Disease. M. M. Spencer and A. Lebeda, eds. International Atomic Energy Agency (IAEA), Vienna, Austria, 2010 (4) A. Lebeda and M. P. Widrlechner. J. Plant Dis. Protect. 110:337, 2003.

Distribution, Host Range and Disease Severity of Pseudoperonospora cubensis on Cucurbits in the Czech Republic

“…Infection of C. melo was recorded only at two locations (2003 in Oplocany, Olomouc region; 2004 and 2009 in Olomouc‐Holice, Olomouc region). Infection of C. moschata was first observed in the Czech Republic in Nový Jičín‐Kojetín (North Moravia – Silesia region) in 2009 (Pavelková et al. 2011).…”

“…2010). The first detection of P. cubensis in Cucurbita moschata in the Czech Republic was in 2009 (Table 3; Pavelková et al. 2011).…”

Coincidence of virulence shifts and population genetic changes of Pseudoperonospora cubensis in the Czech Republic

“…In the Czech Republic, the virulence structure and dynamics of P. cubensis populations are highly variable (Lebeda et al ., ). Since 2009, pronounced structural and temporal shifts in the virulence of the P. cubensis population have been observed (Lebeda et al ., ,b), with the appearance of new pathotypes and new host species such as C. lanatus , C. moschata , C. maxima and C. pepo affected (Lebeda et al ., , ,b; Pavelková et al ., ).…”

“…In 2003 new aggressive pathotypes appeared in Israel and Italy, and highly aggressive isolates ravaged cucumber growing areas of North Carolina, Delaware, Maryland and Virginia in the USA in 2004 (reviewed by Lebeda & Cohen, ; Holmes et al ., ). In 2009 a dramatic change in the pathogen population was observed in the Czech Republic, with new pathotypes and infections on new host species ( Citrullus lanatus , Cucurbita moschata , Cucurbita maxima , Cucurbita pepo ), which had not been previously observed, but occurred repeatedly since then (Lebeda et al ., , ,b; Pavelková et al ., ).…”

Structure and temporal shifts in virulence of Pseudoperonospora cubensis populations in the Czech Republic

“…moschata was recorded at two locations in the Czech Republic (Nový Jičín‐Kojetín, Silesia region of Moravia, 2009–2011; Olomouc‐Holice, central Moravia, 2010) (Lebeda et al. , 2011; Pavelková et al. , 2011).…”