P-694 - Rice sheath blight (Rhizoctonia solani AG1) progress curves for a diverse rice breeding panel

Sheath blight (SB; Rhizoctonia solani AG1), is a major global rice disease. Breeding efforts using only SB severity as a trait have had limited success. This study explores the use of disease progress curves models as an alternative metric to segregate breeding lines. During the 2024 season, a subset of 241 long-grain lines from the US Breeding Germplasm Panel was planted on two planting dates (March 15 and April 26). Plots (1.8x0.6 m) were inoculated with R. solani at the BBCH-30 growth stage. SB was visually assessed as the average SB lesion high (from 0 to 9). The disease was assessed four to five times from 15 to 70 days after inoculation. The study was conducted on a RCBD with two replications per trial. Monomolecular, exponential, logistic, and Gomperts populations growth models were fitted. The best fit was quantified using AIC, R² and plot visual assessment. For the first planting, the logistic (71.2%) followed by the Gompertz (21.4%) models best described the epidemics. In the second planting, models had similar performance; the exponential model explained 31.7% of epidemics, followed by the logistic (24.3%), monomolecular (23.2%), and Gompertz (20.3%) models. Logistic model rates ranged from 0.03 to 0.63 in the first planting and 0.02 to 0.3 in the second. This study shows the diversity of disease progress between lines and planting dates, suggesting that the use of disease progress curves need to be controlled by the environment. Future studies will explore the stability and heritability of the models’ coefficients and their application on breeding selection.