The role of ammonium, calcium, and ethylene in the development of the physiological disorder early bunch-stem necrosis of Vitis vinifera L. c.v. 'Cabernet Savignon'

Abstract

Early bunch-stem necrosis (EBSN) is a physiological disorder which can severely affect fruit set in grapevines. Poor set due to EBSN has been responsible for up to 50% crop losses in many New Zealand and Californian vineyards. The specific cause(s) of EBSN are unclear. Involved researchers presently acknowledge EBSN's correlation with site specific stress(es), with most maintaining that EBSN is the grapevines acclimation response to a reduced carbon status, with damage symptoms mediated through elevated rachis NH₄⁺ levels.

The experiments reported here investigated the influence of NH₄NO₃, (NH₄)₂SO₄, CaCl₂, ethephon, and α-ketoglutarate treatments on the leaf and opposing inflorescence of single node Cabernet Sauvignon (Vitis vinifera L.) cuttings. Results from these investigations concluded that:

• Incubation of cuttings in ethephon concentrations of 0.1 and 1 mM induced significant levels of EBSN. • Incubation of cutting in 10, 20, 30 mM NH₄NO₃, 5, 10, 15 mM (NH₄)₂SO₄, and 10, 20, 30 mM CaCl₂ induced only 'EBSN-like symptoms'. • Incubation of cuttings in 0.1, 1, and 10 mM α-ketoglutarate induced no significant reduction in EBSN or EBSN-like symptoms.

Secondly ethylene production levels by excised grape inflorescences following NH₄NO₃, (NH₄)₂SO₄, CaCl₂, ethephon, and α-ketoglutarate treatments were measured. Conclusions drawn from investigations were that:

• Incubation of cuttings in 0.1, 1, and 10 mM ethephon significantly increased ethylene production by excised grape inflorescences. • Incubation of cuttings in NH₄NO₃ or (NH₄)₂SO₄ treatments did not significantly influence ethylene production by the excised inflorescence. • Incubation of cuttings in CaCl₂ treatments did not significantly influence ethylene production by the excised inflorescence. • Incubation of cuttings in 0.1, 1, and 10 mM α-ketoglutarate treatments significantly increased ethylene production by excised grape inflorescences.

The above conclusions clearly support the involvement of ethylene in the development of, and manifestations associated with, EBSN. The involvement of NH₄⁺, Ca²⁺ and α-ketoglutarate however remains unclear.