Potato Breeding Populations. Abstract Approved: s4-iI14/)

Virus contamination in a potato breeding program can seriously disrupt the variety development process. Experiments were conducted from 1989 through 1993 to: evaluate the extent to which Potato Leafroll Virus (PLRV) and Potato Virus Y (PVY) can invade a breeding program, determine viral spread within hills and within individual tubers, and compare viral detection methods. Enzyme-linked immunosorbent assay (ELISA) of tuber sap for PLPV was most accurate when samples were taken from stem end eyes. Virus titer levels decreased from stem to bud ends. False negative tests were sometimes frequent with tuber testing, but false positives were rare. ELISA of grow-out plants was more accurate than tuber sap ELIA for detecting PLRV. Testing accuracy was further improved by growing plants from tuber bud end eyes because of improved emergence and survival. Visual inspection of grow-out plants was less effective than either foliar or tuber ELISA for determining the presence o