Evaluation of Leaf Contours of the Leaf Lettuce “Greenwave” Using an Elliptic Fourier Descriptor

Abstract

To investigate the effects of different types of irradiation on the growth and morphological characteristics of leaf lettuce (Lactuca sativa L. var. crispa "Greenwave"), a quantitative analysis of the leaf contour using an elliptic Fourier descriptor (EFD) was carried out together with conventional measurement methods. Two experiments were conducted to test the different treatments. Experiment 1 investigated the effects of monochromatic/alternating/simultaneous red/blue irradiation, and Experiment 2 determined the effects of random variations in photosynthetic photon flux density (PPFD) compared with that of constant light. The growth and morphological characteristics in Experiment 1 were consistent with those of previous studies, where the shoot fresh weights in monochromatic and alternating irradiations were larger than those in simultaneous irradiations. EFD showed that the leaf length and petiole under monochromatic and alternating irradiation were longer and more apparent than those under simultaneous irradiation. In Experiment 2, both the conventional measurement methods and EFD could hardly detect any differences in leaf lettuce growth and morphological characteristics under constant PPFD. These results suggested that fluctuating PPFD within certain limits in a PFAL may have little effect on the leaf lettuce growth.