The influence of supplementary lighting and mechanically-induced stress during plant raising, on transplant and maturity characteristics of crisp lettuce

Abstract

SummaryIn experiments in 1984 and 1985 supplementary lighting was given with either tungsten or high-pressure sodium lamps, for 4h, either after dusk or before dawn. Mechanically-induced stress (MIS) was applied by brushing seedlings either every 2 or 4 days for 45 or 90 s on each occasion. Supplementary tungsten lighting increased transplant dry weight and both lamp types tended to increase leaf length. The effects on leaf length were greater when the lighting was applied at dawn rather than at dusk. Transplant weight and leaf length were reduced by brushing seedlings, and these effects increased with increasing frequency and duration of brushing. However, there were no effects of any treatment on head weight at maturity, the coefficient of variation of head weight or the timing of maturity. It is concluded that supplementary lighting during plant raising under glass is unlikely to aid control of mean head weight from one transplanting to another whereas MIS has potential for improving the handling chara...