APPROACHES FOR MANAGEMENT OF SILVER SCURF OF POTATO

Purnima Puri

doi:10.7273/000007448

Silver scurf of potato (Solanum tuberosum L.), caused by Helminthosporium solani, is a surface blemish disease negatively impacting tuber quality and market value. Despite its widespread prevalence in the U.S., the effect of geographic location on silver scurf development in fields remains unclear. Hence, trials were conducted in 2022 and 2023 at Mount Vernon, WA, and Hermiston, OR in fields with undetectable soilborne inoculum. H. solani-infected potato seed tubers were planted in a randomized complete block design with four replications at both locations. Significantly greater incidences of H. solani were observed on daughter tubers sampled from Mount Vernon (mean of 50.8% in 2022 and 43.0% in 2023) compared to those from Hermiston (0% in 2022 and 5.7% in 2023). Similarly, silver scurf consistently was more severe on daughter tubers three months after harvest from the Mount Vernon trial (55.8 disease severity index (DSI) in 2022 and 45 DSI in 2023) compared to the Hermiston trial (0 DSI in 2022 and 7.7 DSI in 2023). A greenhouse trial was conducted using soil from both locations (non-autoclaved field soil and autoclaved field soil from Hermiston, and non-autoclaved field soil from Mount Vernon) to assess the effect of soil on H. solani incidence, silver scurf severity, and H. solani DNA concentration in rhizosphere and geocaulosphere soil. No significant differences in H. solani incidence, silver scurf severity, and H. solani DNA concentration were observed among the three soil treatments (P > 0.05). A second greenhouse trial evaluated the impact of two volumetric soil water content treatments (0.1 and 0.2 m3/m3) and four soils (non-autoclaved field soil and autoclaved field soil from each of the Mount Vernon and Hermiston trial sites). None of the four soil treatments impacted disease development, but plants exposed to 0.2 m3/m3 volumetric soil water content had significantly more silver scurf (41%) compared to plants grown at 0.1 m3/m3 (24.6%). Mycelial growth inhibition assays were conducted to evaluate the sensitivity of 75 H. solani isolates to different concentrations of three fungicides: azoxystrobin (FRAC 11), difenoconazole (FRAC 3), and fludioxonil (FRAC 12). Mean absolute EC50 value for azoxystrobin and difenoconazole were 0.72 and 0.26 μg/ml, respectively, with one isolate exceeding the highest concentration tested for azoxystrobin (10 μg/ml). Most H. solani isolates (67 out of 75) had EC50 values >100 μg/ml for fludioxonil. Furthermore, minituber inoculation assays were used to screen 19 potato genotypes for resistance to H. solani. Although none of the genotypes completely inhibited sporulation of H. solani, the fewest conidia were recovered from genotype A12164-5 (7,113 conidia/g of minituber in trial I and 19,591 conidia/g of minituber in trial II), warranting further screenings focusing on genotypes from the A12164-5 lineage. To summarize, this study demonstrated that geographic location of a field and soil moisture play important roles in the development of silver scurf of potato, which should be considered when developing strategies for managing this disease.

APPROACHES FOR MANAGEMENT OF SILVER SCURF OF POTATO

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