The United States potato industry has recently experienced a strain shift; recombinant potato virus Y (PVY) strains (e.g., PVYNTN) have emerged as the predominant strains over the long dominant ordinary strain (PVYO), yet both are often found as single infections within the same field and as mixed infections within individual plants. To understand mixed infection dynamics in potato plants and in daughter tubers, three potato varieties varying for PVY resistance, 'Red Maria', 'CalWhite', and 'Pike', were mechanically inoculated either at the pre- or postflowering stage with all possible heterologous isolate combinations of two PVYO and two PVYNTN isolates. Virus titer was determined from leaves collected at different positions on the plant at different times, and tuber-borne infection was determined for two successive generations. PVYNTN accumulated to higher levels than PVYO at nearly all sampling time points in 'Pike' potato. However, both virus strains accumulated to similar amounts in 'Red Maria' and 'CalWhite' potato early in the infection when inoculated preflowering; however, PVYNTN dominated at later stages and in plants inoculated postflowering. Regardless of inoculation time, both virus strains were transmitted to daughter plants raised from the tubers for most isolate combinations. The relative titer of PVYNTN and PVYO isolates at the later stages of mother plant development was indicative of what was found in the daughter plants. Although virus titer differed among cultivars depending on their genetics and virus isolates, it did not change the strain outcome in tuber-borne infection in subsequent generations. Differential virus accumulation in these cultivars suggests isolate-specific resistance to PVY accumulation.
Keywords: CalWhite; PVY; Pike; Red Maria; daughter tubers; isolate-specific resistance; pre- and postflowering inoculation; strain interaction; tuber-borne infection.