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.