Flower biology and ontogeny of the tung tree ( Vernicia fordii Hemsl.)

Low number of pistillate flowers in the tung tree is a major factor causing the low yield of tung fruits. The tung tree (Vernicia fordii Hemsl.), an economically important woody oil plant, produces excellent fast-drying oil from the seeds which has been used as a protective finish on projects and surfaces for centuries. Knowledge of sex determination and flower development of tung trees is helpful for high-yield cultivation and breeding of new elite cultivars. However, studies on tung flower biology and ontogeny are still lacking. Here, we reported a comprehensive study of the flower biology and ontogeny of the tung tree, focusing on flower cycle, flower morphology and flower development. The inflorescence phenophases of monoecious tung trees were divided into 12 pivotal stages and used as a unique timeline to reference the events registered throughout the flower cycle. Histological studies on sporogenesis and gametogenesis were also conducted. Meanwhile, all the unique events throughout flower cycle were linked together to show the correlation between inflorescence development phenophases, pistillate and staminate flower stages and its embryological development. Tung trees in our plantation were grouped into three major types, i.e., monoecious, gynoecious and androecious trees which produced different number of fruits in each inflorescence. We propose that low number of pistillate flowers in the tung tree is a major factor causing the low yield of tung fruits, and that any measures increasing the number of pistillate flowers would effectively improve the yield of tung fruits.