Graduate Thesis Or Dissertation
 

Girdling and shading effects on inflorescence necrosis and rachis composition of pinot noir grapevine

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  • 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.
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