Evidence of potato virus Y asymptomatic clones in diploid and tetraploid potato-breeding populations

Potato virus Y (PVY) is a potyvirus affecting potato productivity by reducing yield and quality. To reduce the amount of PVY in potato production systems, state seed certification agencies have established threshold criteria, which simultaneously increase quality. Research has documented several commercial cultivars lacking symptom expression of PVY despite infection. The presence of PVY asymptomatic clones in production and breeding populations is particularly important because it may provide an inocalum source in breeders' seed and this reduces the efficiency of selection. The objectives of this research were to determine to what extent PVY asymptomatic clones are present in potato-breeding populations, and if PVY expression is influenced by the environment. After exposure to PVY, genotypes from different 2x and 4x populations were evaluated for the presence of PVY both visually and by ELISA assay. PVY asymptomatic genotypes were identified in both 2x and 4x populations. Chi square indicated dependency between PVY symptom expression and (1) ploidy, (2) genetically distinct 4x germplasm enhancement populations, and (3) expression in a north temperate vs. tropical environment using 4x progeny from five half-sib families. Dependency was not found between two 4x genetically related sub-populations and PVY asymptomatic expression. Analysis of variance (ANOVA) indicated that clones within family, families, location, and the interaction of location by clone were significant sources of variation for PVY symptom expression, ELISA, and visual evaluation. PVY asymptomatic clones were present in both 2x and 4x populations with higher frequencies in a north temperate compared to a tropical environment, suggesting that PVY symptom expression may be influenced by the environment.