Screening of Barley Genotypes for Resistance to Pyrenophora teres f. teres under Controlled Inoculation Conditions

Net blotch, caused by Pyrenophora teres Drechsler, is a major constraint on barley production. We assembled a panel of 276 spring barley genotypes from 18 countries and evaluated resistance to net form net blotch (P. teres f. teres) using lesion scoring after controlled artificial inoculation of detached leaf segments. Inoculum identity was verified by species-specific PCR, confirming the presence of P. teres f. teres (378 bp) and the absence of P. teres f. maculata. To track inoculum performance and normalise lesion scores, three reference barley genotypes (‘Pax’, ‘P22-SP’, ‘Polo’) were included in every inoculation run. Across 26 inoculation time points, lesion severity in reference barley genotypes remained within a narrow, biologically consistent range, indicating stable yet discriminatory infection pressure. Two independent datasets of 276 barley genotypes showed similar distributions of relative lesion score (paired non-parametric test: no shift in central tendency). At the genotype level, categorical agreement between datasets was high: 62.0% exact matches, 37.7% one-step differences and 0.4% ≥2-step differences. Rank concordance was moderate (Spearman ρ = 0.619; Kendall τ_b = 0.584; both p < 0.001), and chance-corrected agreement was fair (Cohen’s κ ≈ 0.36 – 0.40), driven mainly by Susceptible ↔ Intermediate reclassifications. Thirty-four genotypes were consistently classified as resistant or highly resistant in both datasets; three (‘Romans’, ‘SK-3212’, ‘Svit’) showed particularly low within-genotype variability across replicates, indicating stable expression of resistance. These results demonstrate the robustness and reproducibility of the phenotyping pipeline and identify promising germplasm for resistance breeding against net form net blotch.