BACKGROUND: Several diseases threaten cereal production and fungicides are therefore widely used. Biological control is an environmentally friendly alternative and the fungus Clonostachys rosea is a versatile antagonist, effective against several plant diseases. We studied the ability of C. rosea to control barley leaf pathogens and the mechanisms behind the inhibition emphasising induced resistance.

RESULTS: Under controlled conditions, spray application of C. rosea isolate IK726 to barley leaves reduced Bipolaris sorokiniana severity up to 70% when applied 24 h before or simultaneously as the pathogen, whereas application 24 h after the pathogen had no effect. IK726 also reduced the sporulation capacity of B. sorokiniana. Microscopy of B. sorokiniana infection revealed that IK726 primarily inhibited conidial germination and appressorium formation while further pathogen development and host defence reactions (papillae and fluorescent epidermal cells) were unaffected. Likewise, expression of defence-related genes encoding PR-proteins was unaltered. In addition to B. sorokiniana, IK726 also reduced infection by Drechslera teres and Rhynchosporium commune.

CONCLUSION: C. rosea acted as a protectant against three barley leaf pathogens. B. sorokiniana was directly inhibited by IK726 whereas induced resistance appeared not to be involved. Quantitative microscopy is a powerful tool for elucidating mechanisms involved in disease control.