FIeld experiment was carried out at the Orchard faculty of Agriculture. Assiut
University during three consecutive seasons 2001. 2002 and 2003 on 6-years-old
Thompson Seedless grapevines, planted at 1.5x 3 meter in a loamy clay soil. Yeast
and lor hydrogen cyanamide (He) and the time of application affected on the
percentage of bud fertility and the results were greatly variable with no trend from
season to another; but the highest percentage showed by application of yeast at May.
Yeast or He significantly inhibited catalase activity and increased bud burst.
Application of He at January advanced the timing of bud burst. and gave earliness by
about one month compared to control or application of yeast. In the same trend. yeast
earlier period from bud burst to full bloom by one - three weeks; hence the vines of all
treatments reached full bloom on 10-18 April. Application of yeast at April and May
significantly increased fruitful buds. Most treatments improved vine vigor indica1ed by
increasing the shoot length and thickness, number of leaves and leaf area. All
vegetative parameters have reflected on the metabolism and parallelly increased the
mass of pruning WOOd, total yield and contents of total carbohydrates and nitrogen in
canes. Berries number per bunch and bunch weight were correlated with the weight of
rachis. The best juice quality with decreased lotat acidity and increased TSS/acid ralio
was obtained by application of yeast at April and May, or when used in combination
with He.