Abstract
Molecular marker analysis allow for a rapid and advanced pre-selection and resistance screenings in plant breeding processes. During the phenotyping process, optical sensors have proved their potential to determine and assess the function of the genotype of the breeding material. Thereby, biomarkers for specific disease resistance traits provide valuable information for calibrating optical sensor approaches during early plant-pathogen interactions. In this context, the combination of physiological, metabolic phenotyping and phenomic profiles could establish efficient identification and quantification of relevant genotypes within breeding processes. Experiments were conducted with near-isogenic lines of H. vulgare (susceptible, mildew locus o (mlo) and Mildew locus a (Mla) resistant). Multispectral imaging of barley plants was daily conducted 0–8 days after inoculation (dai) in a high-throughput facility with 10 wavelength bands from 400 to 1,000 nm. In parallel, the temporal dynamics of the activities of invertase isoenzymes, as key sink specific enzymes that irreversibly cleave the transport sugar sucrose into the hexose monomers, were profiled in a semi high-throughput approach. The activities of cell wall, cytosolic and vacuole invertase revealed specific dynamics of the activity signatures for susceptible genotypes and genotypes with mlo and Mla based resistances 0–120 hours after inoculation (hai). These patterns could be used to differentiate between interaction types and revealed an early influence of Blumeria graminis f.sp. hordei (Bgh) conidia on the specific invertase activity already 0.5 hai. During this early powdery mildew pathogenesis, the reflectance intensity increased in the blue bands and at 690 nm. The Mla resistant plants showed an increased reflectance at 680 and 710 nm and a decreased reflectance in the near infrared bands from 3 dai. Applying a Support Vector Machine classification as a supervised machine learning approach, the pixelwise identification and quantification of powdery mildew diseased barley tissue and hypersensitive response spots were established. This enables an automatic identification of the barley-powdery mildew interaction. The study established a proof-of-concept for plant resistance phenotyping with multispectral imaging in high-throughput. The combination of invertase analysis and multispectral imaging showed to be a complementing validation system. This will provide a deeper understanding of optical data and its implementation into disease resistance screening.
Highlights
The ascomycota Blumeria graminis f.sp. hordei (Bgh) is an obligate biotroph organism and the causal agent of barley’s powdery mildew
Cell wall invertase activity increased over the experimental period (Figure 1A)
Investigations by Brugger et al (2017) highlighted a decreased photosynthetic rate and an increased non-photochemical quenching of mlo3 and Mla1 leaves inoculated with Bgh
Summary
The ascomycota Blumeria graminis f.sp. hordei (Bgh) is an obligate biotroph organism and the causal agent of barley’s powdery mildew. Hordei (Bgh) is an obligate biotroph organism and the causal agent of barley’s powdery mildew. It infests leaves and all green parts of barley plants. After the pre-penetration stage which finished with the penetration of the epidermal cell 15 hai, the post-penetration stage starts with an invagination of the fungus inside the epidermal cell. After this entering, Bgh develops a haustorium in the periplasmatic space 24 hai (Francis et al, 1996; Pryce et al, 1999). Different plant-pathogen interactions have specific impact on the plant physiology and histology which individually influence the spectral reflectance signature of plants (Mahlein et al, 2012; Wahabzada et al, 2015)
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