In Xishuangbanna, Mexican sunflower begins flowering in October every year, achieves its
peak bloom in November to December, and mature achenes (hereafter called seeds, although
technically they are dry fruits) are shaken off by wind in January to March the following year.
These seeds pass through March and April, the hot dry season, on the ground, before their germination
requirements are met during the rainy season, from May to October [5, 7].
Seeds used in this study were collected from Menglun, where Xishuangbanna Tropical
Botanical Garden, Chinese Academy of Sciences (21°55' N, 101°15'E) is located, in February
2015. After collection, seeds were air-dried in ambient conditions for a few days, with debris
removed, and then initial moisture content and seed weight were determined, and initial viability
assessed using methods described below. The remaining seeds were sealed in a polyethylene
bag and kept at 15°C.
The seed had been stored at 15°C for about 2–3 months before the following experiments
were performed in April-June 2015. After withdrawal from storage conditions, the seeds were
first dried with silica gel for two days and then rehydrated over saturated air at 30°C for 24 h. A
preliminary test found that this pretreatment can greatly improve seed germination, from 30%
to 90%.