Plant biostimulants in combination treatments as environmentally-friendly rest-breaking agents for dormancy release in table grapes Vitis vinifera Crimson Seedless

Abstract

Context and purpose of the study. Vitis vinifera grapevine is a perennial crop which is globally cultivated, surviving cold winters in temperate zones by entering a state of dormancy. In spring, bud dormancy is released by increasing day lengths and warmer temperatures. Rapid, even bud break is vital to ensure optimal crop yield and carry out effective management practices. Hydrogen cyanamide (HC) is commonly applied to ensure optimal and uniform bud break. Due to the toxicity of HC, alternative environmentally-friendly treatments are sought by the South African Table Grape industry (SATI). This project aims to combine candidate biochemical agents (e.g., nitric oxide donors) with plant biostimulants (Lumichrome, BC204, SNH and PBXH) to enhance bud break in eco-dormant buds.

Material and methods. V. vinifera Crimson Seedless plant material from the 9-year-old CS block (Ramsey rootstock) at Windmeul Farm, Hoekstra Fruit, Paarl, Western Cape, South Africa was used to generate single node cuttings for forced bud break assays in the glasshouse. Combining the selected plant biostimulants with a number of biochemical agents e.g. nitric oxide donors were tested. A small-scale field trial was started on the 6 September 2022, during which the effect the two biostimulants SNH and PBXH were evaluated against HC.

Results. The molecular mode of action of HC has been well studied over the last 20 years. Several models detailing mode-of-action exist in the literature. HC inhibits catalase and induces hypoxia, activating a complex molecular cascade within bud tissues. The levels of reactive oxygen species (ROS) increase significantly, carbon flux is modulated, and phytohormone levels change. These events lead to the activation of transcription factors associated with growth resumption and cell expansion.  Candidate biochemical agents (e.g., nitric oxide donors) provided useful and effective in combination with selected plant biostimulants (SNH and PBXH) in enhancing onset and final bud break % in Crimson Seedless. Further work is needed to consolidate and re-confirm these findings.