Relationships between Growth in Volume and Respiration of Cucumber Fruit Attached on the Vine

Abstract

Studies on the relationships between growth rate in volume and respiration rate of cucumber fruits attached on the vine were begun when they were about 9cm in length.
As fruits grew, those held in individual constant temperature chamber in which the temperature was maintained between 10° to 35°C showed a decrease in respiration rate per fruit volume (R/V) without exhibiting an apparent diurnal fluctuation. The R/V for the first day increased linearly as the fruit temperature became higher. Daily mean values of R/V for the whole measurement period were linear to the relative growth rate (RGR) in volume with the same regression line irrespective of fruit temperature (r=0.95). The intercept of R/V at RGR=0 was comparataively small.
The amount of respired CO₂ (ΔR) from fruit, which varied at different temperatures and age of fruit, was proportional to the increment of fruit volume which occurred during the same period (ΔV), with a regression equation having a proportionality constant of 13.2mg CO₂cm^-3 irrespective of fruit temperature (R²=0.95). Overall conversion efficiency estimated using the proportionality constant obtained above was 86% and it was influenced little by fruit temperature.
The proportionality between ΔR and ΔV indicated that the respiration rate of fruit can be used to monitor nondestructively the fruit growth in dry weight. Consequently, in modeling fruit growth of cucumber, separation of fruit respiration into growth and maintenance components is practically unnecessary.
There was no difference in the relationship between growth in volume and respiration in two cucumber cultivars, i.e., ΔR/ΔV was nearly constant.