Studies on the Embryo Dormancy in Grape.

Abstract

To clarify the phenomenon of embryo dormancy in grape, histological observations of embryogenesis, germinability to embryos at different stage of development, and the onset of embryo dormancy in various grape cultivars were made and/or tested. 1. The growth curve of 'Koushu' grape berries exhibits a double sigmoidal curve. Each fertilized egg divided itself into 2 to 7 cells at 3 to 4 weeks after full bloom (WAFB), then developed into a globular embryo a week to two weeks later; it became heart-shaped at 7 WAFB. The embryo acquired a torpedo-shape at 7 to 8 WAFB; and finally attained full size of about 2 mm in dia. at 10 WAFB, which, time-wise, corresponds to the end of the first growth stage. 2. Embryo rescue culture was conducted on an agar medium (0.7%) prepared by adding vitamins, sucrose (3%), and malt extract (500 ppm) to the MS medium. In 'Koushu' grape, the % germination of globular immature embryos on the agar medium at 6 WAFB was low and the subsequent seedling growth in vitro was poor. Excised torpedo-shaped embryos germinated readily and gave rise to normal seedlings. Full-sized embryos at 12 WAFB and thereafter did not germinate. 3. The onset of embryo dormancy, as indicated by the failure of embryo to germinate in aseptic culture, occurred soon after the veraison stage in all cultivars tested, and it was earlier in early maturing cultivars (e.g. 'Campbell Early') and much later in late maturing cultivars (e.g. 'Koushu'). There was a close relationship between berry maturity and seed (embryo) dormancy.