Light intensity affects the coloration and structure of chimeric leaves of Ananas comosus var. bracteatus

Ananas comosus var. bracteatus is an important tropical ornamental plant because of its green/white chimeric leaves. The accumulation of anthocyanin makes the leaf red especially the white margin. However, the leaves lost red color in summer and winter. Light intensity is one of the most important factors affecting leaf color along the season. In order to understand the effects of light intensity on the growth and coloration of the chimeric leaves, Ananas comosus var. bracteatus was grown under full sunlight, 50% shade and 75% shade for 75 days to evaluate the content of pigments, the color parameters (value L*, a*, b*) and structural histocytology characteristics of chimeric leaves. The results showed that high irradiance was beneficial to keep the chimeric leaves red. However, prolonged exposure to high irradiance caused light damage, some of the leaves wrinkled and even burned. Shading decreased the content of anthocyanin and increased the content of chlorophyll especially in the white margin of the leaves. Numerous chloroplasts were found in the mesophyll cells of the white margin part of chimeric leaves under shading for 75 days. The increase of chlorophyll content resulted in better growth of plants. In order to balance the growth and ornamental value of the leaves, approximately 50% shade is suggested to be the optimum light irradiance condition for Ananas comosus var. bracteatus in summer.