Effects of tissue sampling position, primary and secondary infection, cultivar, and storage temperature and duration on the detection, concentration and distribution of three viruses within infected potato tubers

Abstract

Potato tubers infected with Potato virus S (PVS), Potato leaf roll virus (PLRV) or Potato virus X (PVX) and ELISA were used to study effects of three tissue sampling positions, primary and secondary infection, cultivar, three storage temperatures and different storage durations on virus detection (tuber numbers found infected), concentration (A405 values) and distribution within tubers. Numbers of detections were highest in tissue samples from the rose (PVS), heel (PLRV), and, depending on the period of storage, either the heel or rose end (PVX). With all 3 viruses, detection was least reliable and A405 values lowest in central core tissue. PVS was detected most readily in tuber samples of cvs Mondial, Royal Blue, Ruby Lou and White Star, but less readily in cv. Nadine and poorly in cv. Atlantic samples. Its detection was unaffected by whether infection was primary or secondary. In cv. Nadine tubers, PVS detection was poorer at 4° and 10°C (but not at 20°C) after 5 and 13 weeks storage than after 21 weeks storage at 4°, 10° and 20°C. After >1 weeks storage, PVS A405 values were generally low to very low regardless of storage temperature or duration, lowest values occurring with cv. Atlantic. Numbers of tuber samples in which PLRV was detected were highest in cvs Mondial and Atlantic, intermediate in cvs Nadine and White Star, and poorest in cv. Ruby Lou. However, the number of tuber samples in which PLRV was detected was unaffected by storage temperature or duration, or whether infection was primary or secondary. Higher PLRV A405 values were generally obtained with tuber samples of cvs Mondial and Nadine than of cvs Atlantic, Ruby Lou or White Star. No overall differences in PVX detection occurred resulting from cultivar, different storage durations or temperatures or whether infection was primary or secondary. However, in secondarily infected tubers, detection in tissue from the central core was least reliable at 20°C, but most reliable at 10°C. In cv. White Star tubers only, mean PVX A405 values at 20°C were generally the lowest, while those at 10°C were highest. Testing sprouts detected PVS in more tubers than direct tuber testing, especially with cv. Atlantic, and generally resulted in higher A405 values than testing tubers stored for >1 week. In some cultivars, testing sprouts for PLRV gave slightly lower detection efficiencies than testing tubers directly, but sprout A405 values were usually higher. With PVX, testing sprouts gave comparable detection and A405 values to testing tuber tissue. When tuber tissue samples tested by ELISA were also tested by RT-PCR, PVS and PLRV were detected in many more or several more tubers, respectively, and PCR bands were obtained with rose, core and heel tissue.