Investigating the phyllosphere mycobiome of the ramularia leaf spot-barley pathosystem

Ramularia leaf spot (RLS) is a relatively recent threat to barley production in Europe, and control of the disease mainly relies on fungicide applications. However, increasing restrictions across Europe on pesticide use, and the rapid evolution of fungicide resistance within Ramularia collo-cygni populations, highlight the need for alternative disease control measures such as biological control. The barley phyllosphere is a potential target for identifying biocontrol agents against RLS. However, limited knowledge is available regarding the barley-R. collo-cygni phyllosphere mycobiome. Here, the impact of various factors modulating the barley phyllosphere mycobiome was explored. Firstly, a digital droplet PCR assay was developed for accurate detection of three main barley pathogens from barley seeds and leaf samples. Then fungal communities were sequenced using Illumina Miseq platform. Barley phyllosphere mycobiome analysis indicated that geographical location, R. collo-cygni, and/or fungicides were the key factors. To determine whether the fungicides or the R. collo-cygni modulated the barley phyllosphere mycobiome at each location, spring and winter barley field trials were conducted at two locations in Ireland. Different fungicide combinations, that had similar chemistries, whilst providing variable levels of RLS control, were applied and fungal communities were sequenced. Mycobiome data indicated a significant overall impact of location on the barley phyllosphere mycobiome. At each location, R. collo-cygni significantly impacted the richness and composition of the fungal communities in the barley phyllosphere, and fungicides were an indirect modulator of barley-R. collo-cygni pathobiome diversity and composition. By using a network analysis approach, various potential biocontrol agents against R. collo-cygni were identified. In this study, barley-R. collo-cygni pathobiome was compared with wheat-Zymoseptoria tritici pathobiome as well. Further in vitro and in planta research is necessary to validate the antagonistic activity of the biocontrols against R. collo-cygni.

Funder

Department of Food, Agriculture and the Marine, Ireland

Publisher

University of Galway

Rights

CC BY-NC-ND

cbn

Collections

University of Galway Theses (PhD Theses)