Evaluation of Lettuce Cultivars Suitable for Closed Plant Production System

Abstract

There are many cultivars in butterhead lettuce (Lactuca sativa L.) and if some of them can perform well in the relatively low light and high temperature condition, the commercial lettuce production become feasible because of the lower electric consumption in the plant factory. Eighteen cultivars were grown in the summer greenhouse under 50% shading condition, and the growth indices of seedling stage were examined in relation to the quality of final products (Expt.l). These cultivars were classified into two groups, namely unsuitable (lower qualities) and suitable (higher qualities). The ratio of leaf length to width and chlorophyll content in the seedling stage closely related to the quality of the final products. Twelve cultivars of both groups were selected from the previous experiment and grown in a closed production system to evaluate the productivity and the quality (Expt.2). The performance of the plants showed a similar tendency with those under the greenhouse condition. Thus, the ratio of leaf length to width and chlorophyll content in the seedling stage were found to be an effective index for the evaluation of the performance of lettuce cultivars.