Mexican sunflower (Tithonia diversifolia (Hemsl.) A. Gray) in the family Asteraceae is a weed native to Mexico and Central America. Introduced into China in early 20th century, it has widely naturalized and is exhibiting increasing invasiveness in South China. As seed germination is a critical developmental phase change in plant life cycle, its adaptation to habitats may be a critical determinant of successful invasiveness for an alien plant.
Dr. WEN Bin of Xishuangbanna Tropical Botanical Garden (XTBG) conducted experiments to investigate the high temperature and water stress on seed germination in the invasive species Mexican sunflower. The researcher compared the results with those previously obtained from bamboo piper which is confined to relatively cool and moist habitats in Xishuangbanna. He expected that Mexican sunflower seeds, which can establish on bare ground, would have broader tolerance to high temperatures and water stress than bamboo piper seeds, which do not establish under those conditions.
 Although water stress conditions restricted seed germination in both Mexican sunflower and bamboo piper, the Mexican sunflower achieved a much higher germination percentage. Similarly for high temperature stress, a significant number of seeds germinated although high temperature also reduced seed viability and impaired seed germination. Mexican sunflower seeds can germinate at higher incubating temperatures. Compared with bamboo piper, Mexican sunflower seeds germinated across a wider range of environmental conditions.
The study found higher stress tolerance in Mexican sunflower seeds, which germinated better under high temperature and water stress than previously-reported bamboo piper seeds. Thus, it can be expected that Mexican sunflower seeds, with the capability of germination under any conditions, are more likely to spread into and colonize new habitats than bamboo piper seeds, with relatively strict germination requirements. The higher tolerance in Mexican sunflower seeds accorded with its stronger invasiveness in Xishuangbanna.
The study entitled “Effects of High Temperature and Water Stress on Seed Germination of the Invasive Species Mexican Sunflower” has been published in PLoS ONE.

Contact
WEN Bin, Ph.D
Center for Integrative Conservation, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, Mengla, Yunnan 666303, China
Tel: 86-13988193898
Fax: 86-691-8715070
E-mail: wenb@xtbg.org.cn