Differential Infection by Barley Yellow Mosaic Disease and Its Impact on Key Agronomic Traits in Barley.

Barley yellow mosaic disease (BYMD), a soilborne viral disease, severely compromises winter barley productivity. This disease is caused by barley yellow mosaic virus (BaYMV) and the barley mild mosaic virus (BaMMV), occurring in either single or mixed infections. To elucidate pathogenesis, 10 barley varieties with differential resistance were systematically analyzed. Virus-specific RT-qPCR revealed distinct accumulation patterns of BaYMV and BaMMV in infected tissues. Crucially, transmission requires temperatures persistently below 10°C for 40 to 54 days, facilitating viral entry into roots followed by rapid systemic movement to leaves. Varieties infected with BaYMV, BaMMV, or both showed variations in relative expression levels of BaYMV/BaMMV even among those infected with the same virus. BYMD resulted in a significant reduction in plant height, internode length, spike number, and grain weight per plant in susceptible barley varieties. Notably, infection with BaYMV alone had a more pronounced impact on agronomic traits compared with infection with BaMMV alone. The agronomic traits exhibited similar reductions across the selected varieties, irrespective of whether they were coinfected with BaYMV and BaMMV or infected solely with BaYMV. Virus detection by ELISA correlated with relative viral expression levels, yielding R2 values of 0.7745 (BaYMV) and 0.6689 (BaMMV). Similarly, disease severity values quantified by standardized area under disease progress stairs (sAUDPS) correlated with relative viral expression levels (R2 = 0.7264 for BaYMV and R2 = 0.4402 for BaMMV). Importantly, higher sAUDPS values were associated with greater deterioration in agronomic traits. Genetic analysis confirmed eIF4E as a key resistance source against BYMD and identified QRym.ZN1-7H as an additional major resistance locus. This study holds substantial implications for barley breeding programs aimed at enhancing disease resistance as it facilitates yield prediction under disease pressure and helps the development of early preventive strategies.