Fruit splitting in grapes: Determination of the critical turgor pressure

Abstract

A technique was devised to measure the internal turgor pressure required for fruit rupture in order to assess resistance to splitting objectively rather than rely solely on field observation. In the laboratory, fruit of uniform maturity and known osmotic potential were immersed in a range of osmotica to create a known turgor pressure at equilibrium. "Critical turgor", the pressure which resulted in 50% of the berries splitting, was approximately 15 atm in grape cultivars prone to splitting and 40 atm in resistant cultivars. Cultural treatments with growth regulators subsequently affected fruit resilience. p-Chlorophenoxyacetic acid lowered critical turgor, while gibberellic acid caused an increase. These laboratory-based observations coincided with field experience. Additional factors in fruit splitting, including berry morphology and anatomy, are discussed.