Evaluation of Organic Carriers for Field Inoculation of <i>Brassica napus</i> With <i>Sclerotinia sclerotiorum</i>

Sclerotinia stem rot (SSR), caused by <i>Sclerotinia sclerotiorum</i>, significantly impacts global <i>Brassica napus</i> (canola/rapeseed) production. Because current management relies heavily on timely chemical and cultural methods, developing host resistance is critical to reduce dependence on fungicides and ensure long-term control efficacy. This study aimed to develop a reliable field protocol using <i>S. sclerotiorum</i>-infected inoculum to induce SSR in <i>B. napus</i> and evaluate partially resistant genotypes identified in controlled environments. Several experiments were conducted to evaluate and optimize inoculation techniques on six <i>B. napus</i> cultivars in a series of laboratory, greenhouse, and field experiments. Of the 12 inoculum carriers assessed, the red rice inoculum was selected for further evaluation in the field because of its efficacy as demonstrated in detached-leaf and whole plant assays and its low cost, reliability of production, and ease of application. Using the field inoculation method developed in this study, we found that the semiwinter Japanese lines 'Chikuzen,' 'Chisaya,' and 'Norin28' had partial SSR resistance under field conditions, suggesting a correlation between glasshouse and controlled-environment stem-inoculation assays and whole plant field screens. It also supports the use of these three cultivars as parental lines for future breeding populations containing SSR resistance alleles. The nondestructive, high-throughput field screening methodology developed in this study enables large-scale, reliable screening of <i>B. napus</i> genotypes under various field conditions using cost-effective, easily sourced red rice inoculum applied uniformly to create consistent disease pressure, and it can include multiple isolates.