Ripening behaviour and responses to propylene in four cultivars of Japanese type plums

The aim of this study was to determine the physicochemical changes in highly coloured cultivars of plums that could be used as a guide to assessing optimum harvest maturity. The patterns of fruit growth and maturation were investigated in the cultivars: Gulfruby, Beauty, Shire and Rubyred. Changes in the rates of respiration and ethylene production, skin colour, firmness, soluble solids concentration and titratable acidity were recorded at intervals from pit-hardening until the fruit were tree ripe. In order to evaluate the role of ethylene in the ripening process, propylene was applied to harvested fruit. Internal ethylene concentrations in the cv. Rubyred were also measured at intervals after pit-hardening either in harvested fruit or fruit attached to the tree. Studies of the changes in the physiological parameters associated with ripening showed that none were suitable for the assessment of harvest maturity in all cultivars of plums. However, this analysis revealed two distinct patterns of ripening behaviour in the cultivars studied. Gulfruby and Beauty showed a typical climacteric pattern of development, whilst Shire and Rubyred exhibited a suppressed-climacteric phenotype. This phenotype appears to result from an inability of the fruit to produce sufficient quantities of ethylene to co-ordinate ripening. However, treatment with propylene showed that fruit displaying the suppressed-climacteric phenotype should still be placed in the climacteric class. This suppressed-climacteric character could be incorporated into plum breeding programs to produce new varieties with improved storage properties. (C) 1997 Elsevier Science B.V.