ROLE OF WATER LOSS IN RIPENING OF 'HASS' AVOCADOS

Increased water loss was induced at different stages of ripening (inhibition, preclimacteric, climacteric and post-climacteric phases) to determine its effect on ripening and the incidence of rots. In addition, to determine whether water loss was acting through or independently of the ethylene pathway, 1-aminocyclopropane carboxylic acid (ACC) content and ethylene forming enzyme (EFE) activity in fruit was determined after water loss treatments. To increase water loss during a ripening phase, fruit were transferred from high humidity conditions (>95% RH) to low humidity conditions (<20% RH) for the duration of that phase before returning to high humidity conditions. Fruit remained at 20°C throughout the water loss treatments and the duration of ripening. Transferring fruit to low humidity conditions during these ripening phases increased water loss by approx. 2.5-3.0%. Increased water loss during the inhibition phase increased the rate of respiration and ethylene production and advanced ripening by approx. 2 days, and decreased the incidence of stem-end rots from approx. 50% in control fruit to approx. 19%. Similarly, when water loss was increased during the preclimacteric, climacteric and post-climacteric phases, stem-end rots were reduced to approx. 35%. Increasing water loss during the pre-climacteric, climacteric or postclimacteric phases also increased the rate of respiration but rates of ethylene production and ripening were not markedly affected. The ACC content increased from 0.12 nmol/g at the end of the inhibition phase to 5.86 nmol/g at the end of the climacteric phase. EFE activity increased with the progression of ripening from 1.261/kg.h at the end of the inhibition phase to 7.521/kg.h at the end of the post-climacteric phase. The greatest increase in ACC content and EFE activity occurred during the climacteric phase It is concluded that water loss during initial stages of ripening affects the rate of ripening and the incidence of rots and thereby strongly impacts on fruit quality. Water loss during the later stages of ripening, i.e. during rapid softening have little or no effect. The effects of water loss on fruit physiology and quality are most likely acting through ethylene biosynthesis