Plant Pathology and Crop Protection

Ramularia collo-cygni on barley

Epidemiology, pathogenicity and host resistance

Ramularia leaf spots (RLS) caused by Ramularia collo-cygni is a relatively novel disease in spring and winter barley. It has been observed since the early 80s in barley fields in different countries, including Denmark(Pinnschmidt and Hovmøller, 2003), the Czech Republic (Minarikova et al., 2003), Germany (Sachs, 2000), Scotland (Jahn et al., 1999), Austria (Huss et al., 1987) and New Zealand (Harvey, 2002) as a typical spotting on barley leaves, sheaths and awns. The disease occurs conspicuously late in the growing season. When the crop has passed the flowering stage, the disease severity in the field may increase dramatically within a few days and become the dominant disease, while no or few symptoms are visible before the stem elongation stages. Disease symptoms appear on foliage after ear emergence and contribute to premature loss of green leaf area (Figure 1).

RLS is characterized by abundant small brown speckles usually with a yellow halo. The spots are often confused with physiological leaf spots (PLS) caused by abiotic factors. The rapid senescence of the leaves (premature ripening) causes economical damage up to 20% to barley quality and yield (Oxley and Havis, 2004; Salamati, 2002).

The deuteromycete Ramularia collo-cygni Sutton and Waller (1988) was identified as the causal agent, causing Ramularia leaf spot disease. The name of the species collo-cygni is derived from the special swan neck shape of the conidiophores, which are forming as bunches of white conidiophores bearing conidia on the lower side of leaves in parallel rows (Figure2).

Understanding the causes of this relatively sudden appearance of R. collo-cygni as a major pathogen will be important in attempts to devise effective control measures. Until now there are two main methods to control the disease: (i) chemical control by the use of suitable fungicides and (ii) the cultivation of resistant cultivars. Finding a screening method in controlled conditions to evaluate resistance in different barley cultivars against Rcc is one of the most important aims of this project. Further, this project seeks to identify resistance sources and develop molecular markers to provide selection tools and improve the selection process for Ramularia resistant genotypes. The greenhouse data are also compared with screening under field conditions at different locations (Figure 3 and 4).

Real Time PCR is optimized in a model system by detecting 0.1 pg of target DNA, which is now applied to quantify Rcc biomass in its host tissue during different growth stages (Figure 5).

In field- and greenhouse experiments with a controlled inoculation system we found strong evidences that the epidemic spread and pathogenicity of R. collo-cygni is closely related to the ontogenetic plant development and distinct alterations in the antioxidative protection system of barley leaves. Our results provide evidence that the antioxidative protection system of the leaves plays a key role in the incidence of Ramularia leaf spot as susceptibility increases dramatically with the age-related breakdown of the antioxidative capacity (Schützendübel et al., 2008). For getting a deeper insight into the development of R. collo-cygni on barley and the epidemiology we developed an in vitro system using leaf segments (Figure 6). This system enables us to compare strains of R. collo-cygni collected from different field sites regarding to differences in pathogenicity as well as to test barley for differences in the resistance against R. collo-cygni dependent on age and genotype.

Funding Institution:

Logo BMEL

Investigator: Nazanin Zamani, PhD student

Supervisor: Prof. Andreas von Tiedemann

Collaborators: Dr. Ruge-Wehling, JKI

References:

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