Abstract
Pythium isolates from diseased and dead bait plants of maize and cress grown in compost or various soils (maize fields, parkland under deciduous trees, grassland) were characterised and tested for pathogenicity to maize (Zea mays L.). In pot tests performed under controlled conditions, pathogenicity of the isolates to maize was apparent by reduction of root and shoot growth, whereas damping-off of maize seedlings was less frequent. Contrarily, pea seedlings were killed by pathogenic Pythium isolates. Pythium isolates from diseased maize seedlings and pathogenic strains from other gramineous plants (P. phragmitis, P. aff.phragmitis, P. catenulatum) were not necessarily more virulent to maize compared to isolates originating from dicotyledonous plants (cress). The most virulent isolates originated from compost and caused a reduction of maize shoot growth of up to 60%. Phylogenetic analysis revealed that they were very closely related to P. ultimum var. ultimum and P. arrhenomanes, respectively. Isolates originating from maize fields, grassland and parkland under deciduous trees, a reference culture of P. arrhenomanes and strains of P. phragmitis, P. aff. phragmitis and P. catenulatum with known pathogenicity on reed were non-pathogenic on maize. Isolates from compost, and from maize fields generally had a higher temperature optimum for mycelial growth (30 °C) and a faster growth rate (1.5–2.0 mm h−1) compared to the isolates from parkland under deciduous trees and grassland soil (20–25 °C, ~1.0 mm h−1), respectively. This study indicates a potential impact of pathogenic Pythium on maize plants even in the absence of visible symptoms.
Highlights
Oomycetes of the genus Pythium are important soilborne pathogens that cause seedling losses worldwide due to pre- and post-emergence damping-off and root rot
Cress was chosen as an additional bait plant due to its fast growth and early onset of damping-off symptoms, allowing to capture a potentially greater number of potentially maize pathogenic Pythium isolates with a broad host range within a short time
Cress sown in compost showed nearly 100% mortality due to damping-off and yielded 24 Pythium isolates while maize plants sown in compost yielded a further 16 isolates
Summary
Oomycetes of the genus Pythium are important soilborne pathogens that cause seedling losses worldwide due to pre- and post-emergence damping-off and root rot. Fewer studies have focussed on the role of Pythium species in monocotyledonous crops, including maize, where they have been identified as a cause of pre-emergence dampingoff (Matthiesen et al 2016) and root rot (Deep and Lipps 1996; Chamswarng and Cook 1985, Ingram and Cook 1990). Pythium has been reported as pathogen of gramineous crops in Japan (Toda et al 2015) and as the cause of stalk rot on maize in China (Song et al 2015).
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