Effect of Shading and Nitrogen Source on Growth, Tissue Ammonium and Nitrate Status, and Inflorescence Necrosis in Pinot noir Grapevines

¹ Department of Fruit Science, Southwest Missouri State University, Research Campus, Mountain Grove, MO 65711
² Department of Horticulture, Oregon State University, ALS 4017, Corvallis, OR 97331.

The effect of 60% shading and nitrogen (N) source on growth, tissue NH₄⁺ and NO₃^- concentrations, and inflorescence necrosis (IN) was investigated in one- and two-year-old potted Pinot noir grapevines. New growth of the vines was significantly reduced by shading and NH₄⁺ feeding resulted in less new growth compared to NO₃^- feeding. The shaded two-year-old vines developed 26.6% IN compared to only 0.6% on unshaded vines. No IN was induced by either NH₄⁺ or NO₃^- feeding treatments. Shading increased tissue NH₄⁺ concentration in most tissues of one-year-old vines with few exceptions and in laminas, petioles, and rachis of two-year-old vines. Two-year-old vines fed NH₄⁺ and/or NO₃^- had a higher rachis, petiole, stem, and young root NH₄⁺ concentration at post-anthesis, compared to the no N control. The NH₄⁺-fed vines had a higher NH₄⁺ concentration than that of NO₃^##-fed vines only in stems at post-anthesis and young roots pre-anthesis, anthesis, and post-anthesis. Tissue NO₃^- concentration of laminas, petioles, stems, and young roots was proportional to the amount of NO₃^--fed to the vines in the root medium. Elevated tissue NH₄⁺ concentration in the rachis of shaded vines and increased incidence of IN suggest that IN is associated with elevated tissue NH₄⁺ levels. NH₄⁺ and/or NO₃^- in culture media is not a source of elevated NH₄⁺ level for IN development.

Key words: shading, nitrogen forms, ammonium, nitrate, growth, inflorescence necrosis, early bunch stem necrosis, Vitis vinifera

Submitted on August 1, 1995

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