Development of an LSU rRNA-Targeted qPCR Assay and Transcriptional Profiling of Defense-Related Genes to Elucidate Barley Resistance to Bipolaris Sorokiniana

Abstract

Spot blotch, caused by Bipolaris sorokiniana, severely limits global barley production. This study characterized five isolates from Bolu, T & uuml;rkiye, and screened 95 barley cultivars for resistance to the most aggressive isolate (B_BS01) using a 1-9 disease severity scale. Cultivars Gazda, Dara, Hilal, Nonius, and Bravo exhibited the highest resistance (Disease severity index: 35.00 %-36.67 %), forming a statistically distinct group. A quantitative PCR assay targeting the LSU rRNA locus of B. sorokiniana was developed, detecting pathogen DNA down to 0.1 pg with high specificity. This assay quantified starkly different colonization dynamics: pathogen DNA was effectively suppressed in resistant cultivars (Dara, Gazda), while it proliferated rapidly in susceptible ones (Merit, B & uuml;lb & uuml;l), resulting in up to 15-fold higher pathogen loads by 4 days post-inoculation. Temporal expression profiling of defense-related genes (PR1, PR2, PR3, PR5, PR10, CSD, LOX, PAL) was conducted in Dara and Merit. Notably, PR1 and PR10 were more strongly induced in Merit (17.06- and 10.56-fold at 72 h post-inoculation), whereas PR3 was preferentially upregulated in Dara. PR5 and LOX were downregulated in both cultivars; CSD showed moderate induction, and PR2 remained relatively stable. The combination of a sensitive qPCR assay and gene expression profiling provides robust tools for resistance screening and supports targeted breeding for spot blotch resistance in barley.