Concentration Dependence of `Redchief Delicious' Apple Fruit Softening and Chlorophyll Fluorescence to Repeated Doses of 1-Methylcyclopropene

Abstract

We studied the dose-response of `Redchief Delicious' apple [Malus sylvestris (L) Mill. var. domestica (Borkh.) Mansf.] fruit to repeated (weekly) dosages of 0.0, 0.02, 0.1, and 1.0 μL·L-1 1-methylcyclopropene (1-MCP) by measuring fruit firmness and chlorophyll fluorescence throughout an extended storage period at 0, 5, 10, 15, and 20 °C. The rate of firmness loss for nontreated fruit increased with increasing temperature. 1-MCP applied at concentrations of 0.1 and 1.0 μL·L-1 slowed firmness loss. The 1-MCP dose-response curve for the rate of firmness loss was essentially the same for all five temperatures. A concentration of 1.0 μL·L-1 1-MCP prevented firmness loss at all temperatures for the duration of the study; however, after holding fruit for an additional 7 days at room temperature, the fruit stored at 10 °C softened with increasing storage duration, whereas fruit at stored at higher and lower temperatures did not. The influence of 1-MCP on chlorophyll fluorescence (Fo and Fm) was markedly affected by temperature; Fo increased during storage at higher storage temperatures and this increase was enhanced by 1-MCP. Conversely, Fm decreased during storage and the rate of decline was much greater at the higher storage temperatures; the rate of decline was reduced by 1-MCP, but only at the higher storage temperatures. Photochemical efficiency (Fv/Fm) of nontreated fruit declined with time for all storage temperatures. Treatment with 0.1 and 1.0 μL·L-1 1-MCP only marginally reduced the rate of decline of photochemical efficiency. Sample loss due to decay increased with temperature, but was reduced by 1-MCP at all temperatures.