Methyl Jasmonate and 1-Aminocyclopropane-1-Carboxylic Acid Interact to Promote Grape Berry Abscission

Abstract

The application of methyl jasmonate (MeJA) or ethephon, an ethylene-releasing agent, to Thompson Seedless grapes can reduce fruit detachment force (FDF) and promote the development of dry stem scars on berries, possibly improving the quality of machine-harvested grapes. However, the amount of MeJA or ethephon needed to stimulate abscission may be prohibitively expensive and result in excessive residues. Thus, experiments were conducted to determine whether MeJA might interact with 1-aminocyclopropane-1-carboxylic acid (ACC), a natural biochemical precursor of ethylene, to promote abscission-related processes and possibly reduce the amount of MeJA needed. In a preliminary trial, MeJA (672 and 1,344 mg/L) interacted with ACC (500 and 1,000 mg/L) to reduce FDF by 25 to 70% compared with untreated grapes. However, MeJA and ACC did not interact to affect preharvest fruit drop, although treatment with 672 or 1,344 mg/L MeJA caused 16 to 23% drop by 3 days after treatment (DAT). In a second trial, grapes treated with MeJA, singly, or with ACC, produced ethylene which peaked at 1 DAT, remained elevated at 2 DAT, and declined rapidly thereafter, whereas grapes treated only with ACC maintained moderately elevated ethylene production throughout the 10-day study. Treatment with ACC or MeJA reduced FDF within 1 or 2 DAT, respectively. By 2 DAT, berries began to abscise from MeJA-treated clusters, regardless of whether they were also treated with ACC, but on 3, 4, and 10 DAT, ACC and MeJA interacted to greatly promote preharvest fruit drop. Moreover, the combination of ACC and MeJA also promoted dry stem scar development. Thus, coapplication of MeJA and ACC is more effective at stimulating grape abscission-related processes than either compound applied singly.