Identification and Characterization of PVYN-Wi Isolates Associated with External Tuber Necrosis in the San Luis Valley (Colorado): A New Challenge for Seed Potato Certification.

Potato (Solanum tuberosum L.) is a major global staple crop, and potato virus Y (PVY) is one of the most economically important viruses affecting potato production worldwide. The San Luis Valley (SLV) produces approximately 95% of Colorado's potatoes and is the second-largest fresh potato-growing region in the United States. PVY is the leading cause of seed potato rejection in the SLV and has contributed to a sustained decline in certified seed potato production over the past two decades. The PVY population in Colorado is dominated by three strains: PVYO, PVYN-Wi, and PVYNTN. PVYN-Wi accounts for approximately 40% of PVY infections in the SLV and its impact on tuber quality remains poorly understood. During the 2023 and 2024 growing seasons, potato tubers exhibiting external necrosis and cracking were submitted to the Potato Pathology Program of the San Luis Valley Research Center for diagnosis. PVYN-Wi was consistently identified in the symptomatic tubers. These results agree with previous studies demonstrating that external tuber necrosis, historically attributed to PVYNTN, may also be associated with PVYN-Wi, under field conditions. As PVYN-Wi belongs to the O-serotype, it is not detected by the N-serotype specific antibodies used in seed certification programs to manage tuber necrotic strains of PVY. Consequently, the contribution of PVYN-Wi to tuber quality losses in the SLV may be underestimated, highlighting the need to reassess PVY diagnostic and management strategies.