Photosynthetic Characteristics and Leaf Coloration Mechanism of the Hybrids between Forsythia ‘Courtaneur' and F. koreana ‘Suwon Gold'

Crosses between Forsythia ‘Courtaneur’ (female parent) and F. koreana ‘Suwon Gold’ (male parent) were conducted in order to breed new Forsythia cultivars with vigorous growth and bright yellow leaves，and fifty two F₁ hybrid progenies with different leaf colors were obtained. The plant growth rate，foliar pigment contents，photosynthetic rate，microstructure and the ultrastructure of chloroplasts of leaves were investigated. The results showed that compared to the parent plants, the chlorophyll content of yellow leaf group was lower，palisade tissue was thinner，and structure of stroma lamella was not clear，so the photosynthetic activity was affected, leading to lower growth potential. The chlorophyll content of plants in the yellow-green leaf group was higher，thickness of palisade tissue was increased，structure of stroma lamella was clear，and the growth potential was improved. The study proved the basis of breeding new Forsythia cultivars with vigorous growth and bright yellow leaves.