Emission of novel volatile biomarkers for wheat powdery mildew

Natural ecosystems including host-pathogen interactions produce a plethora of biogenic volatile organic compounds (BVOCs). Infections by phytopathogens change the volatile profile substantially and dynamically over a crop field or even on a larger scale. Despite their worldwide importance in agriculture little is known about the BVOC emissions of cereal crops, such as wheat, and their pathogens. The wheat-powdery mildew interaction is especially relevant, because powdery mildew is widespread on a global scale and is caused by an obligatory biotrophic pathogen (Blumeria graminis f.sp. tritici, Bgt). Since the BVOCs in this important fungus have still not been identified, the most frequent local natural pathotypes were studied by artificial inoculation and dynamic headspace collection followed by GC–MS analysis in three consecutive years. Of the 48 BVOCs identified in a total of 120 samples, six compounds (1,3-octadiene, 1,3-cis,5-cis-octatriene, 1-heptanol, (5Z)-octa-1,5-dien-3-ol, 1-octen-3-ol and 3-octanone) were detected only in Bgt-inoculated plants, and were hence quantitated. The latter three BVOCs were the most abundant in symptomatic plants with a characteristic distribution pattern. Additional wheat genotypes, different host plant development stages, and early and full disease progression in the presence of other pathogen mixes were also tested for the specificity of the proposed biomarkers. The three major biomarkers, namely (5Z)-octa-1,5-dien-3-ol, 1-octen-3-ol and 3-octanone were robustly applicable for differentiating the headspaces of healthy and mildew-infected plants even at early stages when disease symptoms are barely visible. These novel powdery mildew-related biomarkers are promising candidates for chemotyping and environmental monitoring in the field. [Display omitted] •Agricultural ecosystems emit massive quantities of volatile organic compounds•Volatile compounds identified by GC–MS during the wheat-powdery mildew interaction•Six robust volatile biomarkers released by powdery mildew fungus during infection•These biomarkers monitored for three years, various strains and symptomatic stages•Baseline data for the combination of novel biosensors with machine learning