Fig. 1 Morphological appearance of mature seeds of grape varieties from different proveniences. A, Hilum side (above line) and back side (below line) of seeds; B, Embryos.

Fig. 2 Changes in seed water contents (g H2O g-1 DW) during imbibition of grape varieties from different proveniences. A, Varieties of East-Asia species (S); B, Beichun (O×S), Jingxiu and Jingyu (O), Jingya (O×M) and Concord (M).

Fig. 3 Effects of sulfuric acid treatment on germination of grape seeds. Beta (M); Beihong (O×S); Zuoshanyi (S); Jingyu (O); Jingya (O×M).

Fig. 4 Effects of removal of seed coat surrounding embryo on seed germination and germination of excised embryos. A, Scarified seeds (removed seed coat surrounding embryo) germinated on moistened filter paper; B, Excised embryos germinated on MS medium (no exogenous phytohormone). Different letters show significant difference at P = 0.05 level.

Fig. 5 Stratification effects at different temperatures on seed germination of grape varieties from different proveniences. (A) Varieties of East-Asia species; (B) Europe-Asia species; (C) Varieties of American species, cross-breeds of Europe-Asia species × East-Asia species, East-Asia species × Europe-Asia species, Europe-Asia species × American species; A, B, C: stratified for 2 months at 5°C, 25°C, 20/10°C and 30/20°C. (D) Varieties of American species and Europe-Asia species × American species, stratified for 6 months at 5°C and 20/10°C.

Fig. 6 Germination course of different species of grape seeds at alternate temperatures simulating the season changes. Cycle 1(●): Summer (3 months, 30/20°C)-autumn (3 months, 20/10°C)-winter (3 months, 5°C)-spring (3 months, 20/10°C); Cycle 2 (○): Winter (3 months, 5°C)-spring (3 months, 20/10°C)-summer (3 months, 30/20°C)-autumn (3 months, 20/10°C). Arrows indicate the simulating season changes at which seeds were moved from one temperature regime to the next.