Effects of some biotic and abiotic factors on symptom expression of lettuce big-vein virus in lettuce (Lactuca sativa)

SummaryA nutrient film technique (NFT) system was developed to infect lettuce plants with an isolate of Olpidium brassicae carrying lettuce big-vein virus (LBVV) and to examine the effect of some biotic and abiotic factors on symptom expression of the virus. The NFT system had the advantage of removing any effects due to variation in moisture and allowed continuous and natural infection of test plants. The developmental stage of lettuce plants (5 true leaves) and duration of exposure to inoculum (4 wk) in the NFT system that induced most severe symptoms were determined. Within the temperature range previously reported to favour symptom expression of LBVV (14–18°C), significant differences in symptom severity were detected. Despite previous reports that low temperatures favour symptom expression, the most severe symptoms were induced in the shortest time at 18°C. Compared with diurnal temperature regimes of 10°C night and 18°C day, plants kept at constant 18°C developed more severe symptoms more rapidly. S...