SEED DEVELOPMENT AND ABORTION IN VITIS-VINIFERA L, CV CHARDONNAY

Seed development was investigated by light microscopy in early- and la te-flowering bunches of the grapevine cv. Chardonnay on days 4, 14, 28 , and 42 after the first flowers opened and at berry maturity (98 d). Only ca. 20% of ovules were penetrated by pollen tubes and were fertil ized, as evidenced by a zygote and free nuclear endosperm. Normally, t he first division of the zygote occurred between days 14 and 28 and co incided with cell wall formation in the endosperm. Embryo development was slow from day 14 to 42 but accelerated thereafter. Ovules without an embryo sac did not develop and nucelli degenerated. Those with a no rmal but unfertilized embryo sac aborted after a small amount of testa and nucellus growth, evidenced by a degenerate nucellus. Abortion occ urred also during later stages of seed development, with the testa dev eloping normally but the nucellus and the endosperm degenerating, givi ng a hollow (''floater'') seed. Some floaters were completely empty wh ile others contained degenerating embryos, endosperms, or nucelli. The incidence of floaters was 31% in the bunches where flowering commence d early, and 9% in the bunches dowering 2 wk later in both cases among more than 500 seeds. Empty seeds were mostly the consequence of embry o degeneration followed usually by endosperm degeneration. In cv. Char donnay, three consecutive, possibly interconnected processes are seen as the causes of no or defective transition from ovule to seed: (a) ab errant embryo sac development before flowering, (b) lack of fertilizat ion at flowering, and (c) incomplete development of zygote/embryo afte r flowering. All impair development of berries in which none of the fo ur ovules develop into normal seeds. Preanthesis abortion of all ovule s per flower leads to flower abscission. Berries containing only arres ted ovules and/or seed traces remain small but nevertheless ripen (''c hickens''). Berries with floater seeds but without normal (''sinker'') seeds develop and ripen normally but remain somewhat smaller than ber ries containing sinker seeds.