Abstract:
There are several grape disorders that reduce fruit
set. One, millerandage, is from poor fertilization to
produce "hen and chicken" or small seedless berries; while
another, Coulure, is the failure of grape flowers to
develop into berries. A third one, inflorescence necrosis
(INec), is a disorder that should be in this category.
Inflorescence necrosis is a recently described
disorder that can be an important cause of fruit set
reduction in grapes. INec occurs at bloomtime and the
affected tissue is characterized by brownish or black
coloration. Only clusters are affected by INec. Flowers and
pedicels are the only damaged tissue. Sometimes, the rachis
can also be injured. In severe cases, clusters can be
completely necrotic. The influence of girdling and shading
on INec and fruit set was determined in mature field grown
Pinot Noir grapevines in 1989. Shading with 60% shade cloth
was imposed from one month before bloom through bloom.
Girdling was done one week before capfall. Shading
increased the percentage of necrotic flowers by 2.3 to 2.7
times and reduced fruit set by 23% to 35% compared to
exposed plants. Girdling increased fruit set 15% and 25% in
two vineyard plots compared to ungirdled vines. The effect
of shoot girdling and shoot density on INec was evaluated
in 1990. Shoot density, which was adjusted before bloom,
did not affect INec. Girdling did not influence the
percentage of necrotic flowers in both years.
Free ammonium levels were measured in shoot xylem
exudate, tendril, petiole, rachis, and flower tissue
sampled at three growth stages: beginning bloom, full
bloom, and shatter. In 1990, rachis tissue was also sampled
for ammonium at harvest time. The highest ammonium level
was found in the rachis while the flowers had the lowest.
Rachis ammonium concentration was higher at beginning bloom
and then declined afterward. Shade increased ammonium
concentration 24% and 21% in the rachis at beginning bloom.
In 1989, soluble sugars and organic acids were
determined in the rachis tissue. There was no significant
effect from the girdling or shading treatments on total
soluble sugars concentration. However, girdling increased
rachis dry weight 21% and 33% at full bloom and shatter,
respectively. On the contrary, shading reduced rachis dry
weight 27% at full bloom and 31% at shatter stage. Glucose
level was several times greater than fructose and glucose
in the three sampling periods. Shading reduced 3 0% total
organic acids concentration at beginning bloom, and 2 0% at
full bloom. Tartaric was the predominant acid. Shading
reduced the concentration of a-ketoglutaric acid but no
treatments had a significant effect on its rachis level
during bloom.
