Host plant development, water level and water parameters shape Phragmites australis-associated oomycete communities and determine reed pathogen dynamics in a large lake

Abstract

In a 3-year-study, we analysed the population dynamics of the reed pathogen Pythium phragmitis and other reed-associated oomycetes colonizing fresh and dried reed leaves in the littoral zone of a large lake. Oomycete communities derived from internal transcribed spacer clone libraries were clearly differentiated according to substrate and seasonal influences. In fresh leaves, diverse communities consisting of P. phragmitis and other reed-associated pathogens were generally dominant. Pythium phragmitis populations peaked in spring with the emergence of young reed shoots, and in autumn after extreme flooding events. In summer it decreased with falling water levels, changing water chemistry and rising temperatures. Another Pythium species was also highly abundant in fresh leaves throughout the year and might represent a new, as-yet uncultured reed pathogen. In dried leaves, reed pathogens were rarely detected, whereas saprophytic species occurred abundantly during all seasons. Saprophyte communities were less diverse, less temperature sensitive and independent of reed development. In general, our results provide evidence for the occurrence of highly specialized sets of reed-associated oomycetes in a natural reed ecosystem. Quantitative analyses (clone abundances and quantitative real-time PCR) revealed that the reed pathogen P. phragmitis is particularly affected by changing water levels, water chemistry and the stage of reed development.

Virulence of oomycete pathogens from Phragmites australis‐invaded and noninvaded soils to seedlings of wetland plant species

“…2005; Wielgoss et al. 2009; Mazurkiewicz-Zapalowicz 2010) and Py. litorale (Nechwatal and Mendgen 2006)] (point 3 above), we can only make inferences about how pathogens influence invasiveness based solely on relative abundance and virulence of various taxa to P .…”

“…2008a; Wielgoss et al. 2009). As we have no data on the relative abundance or virulence of pathogens in the native European range of P .…”

“…2006; Wielgoss et al. 2009; Kurokawa and Tojo 2010), the impacts of these pathogens on P. australis and other native and non-native plant species have not been well studied. In both its native and non-native ranges, P .…”

Consequences of the colonisation of leaves by fungi and oomycetes for leaf consumption by a gammarid shredder

“…This strongly suggests that colonisation by oomycetes results in a lower food quality for shredders than colonisation by fungi. Because of the presence of oomycetes in the early stages of conditioning (Wielgoss et al. , 2009), our findings indicate that oomycetes may have a greater impact on early leaf litter decomposition in freshwaters and on the coupling of this process to higher trophic levels than hitherto assumed.…”

Niche differentiation of two sympatric species of Microdochium colonizing the roots of common reed

“…Seasonal variation has been found in an aquatic fungal community decomposing plant debris in streams [45]. In reed stands at Lake Constance, Oomycota populations were shown previously to exhibit seasonal variation [46]. For the reed pathogen Pythium phragmitis , minimal detection in August resembled the decrease of Microdochium spp.…”