2. Materials and methods
2.1. Experiment material and planting
Supersweet corn seeds (F1 hybrid with sh2), cv. Supersweet 17,
were used in these studies. The hybrid seeds were produced by
synchronous hand cross-pollination of the parental inbreds in the field at the experimental farm of Zhejiang University using production practices common for the region.
2.2. Seed harvest
Normally, it takes 30–40 days for supersweet corn seeds to
fully mature but seed germination is possible 14 days after
pollination (Cao et al., 2008b). Supersweet corn ears were
harvested at different developmental stages from 14 to 42 days(at an interval of 4 days) after pollination (DAP). At each harvest,10 plants were randomly chosen and the first ear from the top of the plant was harvested by hand. Seeds from the middle part of supersweet corn ears were threshed by hand and bulked for further tests
2.3. Germination test
Three replications of 50 seeds for each harvest were used, each
50 seeds were placed in a 12 cm 18 cm germination box
containing wet sand. Then, seeds were kept in a germination
chamber at 25 8C with a diurnal cycle of 12 h light and 12 h
darkness for 7 days. Seeds were considered germinated when a
1 mm length radicle protruded through the seed coat. The number
of germinated seeds was counted daily. The energy of germination
and germination percentage were calculated after 4 and 7 days,respectively. The germination index (GI = S(Gt Tt1
)) was calculated by the method of Zhang et al. (2007) where Gt is the number
of the germinated seeds on day t and Tt is the time corresponding
to Gt (in days). The energy of germination was the percentage of germinated seeds 4 days after planting relative to the number of
seeds tested.