Internal Ethylene Concentrations in Apple Fruits Attached to or Detached from the Tree1

A method is described for the measurement of internal ethylene concentration in fruits on the tree. Ethylene levels in ‘Red Delicious’ fruits immediately after harvest were similar to those in fruits on the tree during development and ripening. The levels varied mostly between 0.02 to 0.15 ppm during the period from 83 to 140 days from bloom and sharply increased from 10 to 1000-fold within 5 days as autocatalytic ethylene production began. Ripening followed the upsurge in ethylene production. Isolating fruit from leaves by girdling plus defoliation of spur leaves hastened the increase in internal ethylene by approximately 1 month. Girdling or defoliating the spur did not markedly alter the onset of autocatalytic ethylene production compared to that observed by fruits on normal spurs. The data support the concept that fruits receive a ripening inhibitor from the leaves.