Effect of Geographic Location and Soil Moisture on In-Field Development of Silver Scurf of Potato

Silver scurf of potato ( Solanum tuberosum L.), caused by Helminthosporium solani , is a tuber blemish disease prevalent in the United States. Silver scurf incidence varies widely between geographic locations, and the causes of this variation are not well studied. Hence, three trials were conducted at Mount Vernon, WA, and Hermiston, OR, in fields with undetectable H . solani soil inoculum determined by quantitative real-time PCR assays. Seed tubers of two potato cultivars infected with H . solani were obtained from the same source and planted at both locations in each of 3 years in a randomized complete block design with four replications. Higher incidence of H . solani was observed on daughter tubers from Mount Vernon (51 ± 4% in 2022, 43 ± 4% in 2023, and 48 ± 4% in 2024) than those from Hermiston (0 ± 0% in 2022, 6 ± 1% in 2023, and 0 ± 0% in 2024). Two greenhouse trials were conducted using tubers infected with H . solani grown in nonautoclaved and autoclaved soil collected from both locations (Skagit silt loam soil from Mount Vernon and Adkins fine sandy loam soil from Hermiston). Daughter tubers showed few significant differences in H . solani incidence and silver scurf severity. However, daughter tubers from plants grown at 0.2 m 3 /m 3 soil volumetric water content (VWC; ∼70% of field capacity in Mount Vernon) had greater silver scurf incidence than those exposed to 0.1 m 3 /m 3 VWC (∼70% of field capacity in Hermiston): 41 ± 4% and 40 ± 4% in the first and second trials, respectively, compared with 25 ± 4% and 16 ± 3% at 0.1 m 3 /m 3 . These results suggest that soil moisture is an important factor for the development of silver scurf of potato.