Spore dispersal patterns of the ascomycete fungus Ramularia collo-cygni and their influence on disease epidemics

Abstract

Ramularia leaf spot is a major economic disease of barley caused by the dothidiomycete fungus Ramulariacollo-cygni. The fungus has a complex life cycle which includes extensive late season spore release events and a seed-borne phase. Predicting disease epidemics during the growing season remains a difficult challenge. To better understand the interaction between spore movement and disease epidemics, spore samplers were set up in Germany (two sites over 4 years), Poland (seven sites over 2 years) and the UK (two sites over 9 years), where the disease has been observed. Spore concentrations were determined using a real time PCR assay, and meteorological data were obtained from co-located automatic stations. Spore release events were seen to peak in June on mainland Europe and July in the UK. The pattern of spore release was broadly similar across countries with earlier peaks in mainland Europe. A relationship was observed in the UK between July spore levels and disease in following winter barley crops. Rainfall and temperature were proposed as significant drivers of spore release in these months. The major environmental parameter associated with spore release across the two UK sites was crop surface wetness, although some site-specific interactions were noted for rainfall and wind movement. Regression analysis of spore patterns and disease epidemics indicates a relationship between spore levels 75–105 days pre harvest and final disease levels in UK winter barley crops. This relationship was not observed in spring barley. The implications on risk forecasts are discussed.

Comparative analysis of Argentinian and European populations of Ramularia collo‐cygni on barley

“…The moderate level of differentiation found between European populations supports the results of Stam et al. (2018) who suggested that European Rcc populations form one genetic cluster driven mainly by long‐distance spore dispersal (several kilometres; Brown & Hovmøller, 2002; Havis et al., 2023) and seed exchange between countries.…”

“…Significant differentiation (high to moderate) between all populations included in our study was observed, where the Argentinian population was highly and significantly differentiated from the others. The moderate level of differentiation found between European populations supports the results of Stam et al (2018) who suggested that European Rcc populations form one genetic cluster driven mainly by long-distance spore dispersal (several kilometres; Brown & Hovmøller, 2002;Havis et al, 2023) and seed exchange between countries.…”

“…In Argentina, all barley varieties are susceptible to the disease (Erreguerena et al., 2021). All these characteristics of Rcc, together with its rapid development of resistance to fungicides (Erreguerena et al., 2022; Kiiker et al., 2021; Rehfus et al., 2019), explain how it has spread all around Europe and many other countries and continents as a result of seed exchange (Havis et al., 2015) and on a local scale (several kilometres) by asexual spore dispersal (Havis et al., 2023; Zamani‐Noor, 2011), and hence why Rcc is considered an increasing threat to barley production.…”

“…Europe and many other countries and continents as a result of seed exchange (Havis et al, 2015) and on a local scale (several kilometres) by asexual spore dispersal (Havis et al, 2023;Zamani-Noor, 2011), and hence why Rcc is considered an increasing threat to barley production.…”

Efficient qPCR estimation and discrimination of airborne inoculum of Leptosphaeria maculans and L. biglobosa, the causal organisms of phoma leaf spotting and stem canker of oilseed rape

“…Collection and quantification of airborne fungal propagules are now routine and feature prominently in arriving at both prophylactic and therapeutic decisions for the management and control of plant diseases caused by aerially dispersed fungal inoculum 13,37,38 . Since the initial conception of Hirst‐type air samplers by Gregory 39 and Hirst 40 (reviewed by West and Kimber 41 ), advances in the coupling of the methods of aerobiology and techniques of wind‐dispersed fungal propagule collection, detection and quantification have enabled earlier, easier and more effective decisions in disease management 42–45 . Taken together, the integration of spore trapping with quantitative diagnostic assays such as qPCR can facilitate and enhance a faster and more accurate assessment than by abundance estimation made by spore counting on light microscope slides, particularly if these spores are difficult to identify visually at the species and infra‐species levels, which is very often the case with phytopathogens of important crop plants.…”