TEXTURAL AND PHYSIOLOGICAL-CHANGES DURING PEPINO (SOLANUM-MURICATUM AIT) RIPENING

Pepino fruit (cultivar 'El Camino') softened throughout ripening while attached to the bush. An Instron Universal Testing Machine was used t o define a range of compressive and tensile textural parameters. A nov el tensile test for fruit tissues is described. The pattern of textura l change implied that softening was primarily a result of a progressiv e decline in cell wall strength and loss of cell-to-cell adhesion. In vitro treatments to lower tissue turgor, apoplastic pH, or free calciu m were equally effective in softening tissue rings. Pectinmethylestera se and polygalacturonase (PG) activities increased during ripening. PG activity appeared just before the first externally visible sign of ri pening (purple striping), and increased during the later stages of fru it softening. Pepino fruit are non-climacteric, since propylene accele rated colour change and fruit softening, but fruit produced little eth ylene at harvest and did not produce ethylene autocatalytically in res ponse to exogenous propylene. Fruit respiration increased transiently in response to propylene, but in control fruit the respiration rate in creased only slowly during post-harvest ripening. During prolonged sto rage at 20-degrees-C the only fruit to produce ethylene at rates over 0.2 mul kg-1 h-1 were those which subsequently developed rots.