EFFECT OF SHADING AND NITROGEN-SOURCE ON GROWTH, TISSUE AMMONIUM AND NITRATE STATUS, AND INFLORESCENCE NECROSIS IN PINOT-NOIR GRAPEVINES

The effect of 60% shading and nitrogen (N) source on growth, tissue NH 4+ and NO3- concentrations, and inflorescence necrosis (IN) was invest igated in one- and two-year-old potted Pinot noir grapevines. New grow th of the vines was significantly reduced by shading and NH4+ feeding resulted in less new growth compared to NO3- feeding. The shaded two-y ear-old vines developed 26.6% IN compared to only 0.6% on unshaded vin es. No IN was induced by either NH4+ or NO3- feeding treatments. Shadi ng 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-anthe sis, 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-anth esis and young roots pre-anthesis, anthesis, and post-anthesis. Tissue NO3- concentration of laminas, petioles, stems, and young roots was p roportional 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.