Stress-induced development of inflorescence necrosis and bunch-stem necrosis in Vitis vinifera L. in response to environmental und nutritional effects

Abstract

Inflorescences and mature clusters, respectively, of field-grown Muller-Thugau grapevines ( Vitis vinifera L.) were immersed in aqueous solutions of the glutamine synthetase (GS) inhibitor phosphinothricin (PPT). Typical symptoms of inflorescence necrosis developed after immersion in 1 or 10 mM PPT, but not in the 0.1 mM treatment. No necrotic symptoms could be induced in mature clusters. In addition, single-node cuttings of field-grown Muller-Thurgau and Pinot noir vines with one cluster, with or without adjacent leaf, were incubated in various solutions with or without PPT at several phenological stages. Necrotic symptoms occurred in all treatments including the H 2 O control. However, at early stages of development the symptoms appeared earlier than at later stages, and elevated PPT concentrations reduced the development of necrotic manifestations. The addition of NH,NO, to the solution enhanced the appearance of symptoms both in the presence and absence of PPT, while KNO 3 did not. In incubation solutions without PPT, metallic cations like Mg 2+ , Ca 2+ and K + reduced the incidence of bunch-stem necrosis. When cuttings were exposed to different environmental conditions, there was no significant light effect, but wind decreased the incidence of both inflorescence necrosis and bunch-stem necrosis. A leaf, attached to the cluster, or the addition of sucrose to the solution effectively delayed the development of necrotic manifestations. These results indicate that GS is present in rachis, flower and berry tissues and that the buildup of toxic NH 4+ levels is involved in the development of both inflorescence necrosis and bunch-stem necrosis. However, NO 3 - reduction and primary N assimilation appear not to contribute significantly to NH 4+ accumulation. This buildup may rather be a secondary effect related to senescence of the tissue due to carbon depletion.