No abstract

Bloom application of aminoethoxyvinylglycine (AVG) increased the fruit yields of ‘Ultra Red Delicious’ apple (Malus domestica Borkh.) trees. In one season, sprays of 50 ppm AVG were more effective in increasing yield than those of 500 ppm. In the second season, treatment with 150 and 225 ppm AVG was most effective. High levels of AVG (> 225 ppm) caused excessive fruit set and decreased fruit size. Ethylene evolution from developing fruits and fruiting spurs was decreased by AVG treatment.

In the past three years we have studied the effects of oxygen on the maturation and ripening of `Gala' apples. Fruit-respiration, the onset of the climacteric rise in ethylene evolution and the rate of increase in ethylene production were measured. The effects of oxygen on softening and titrable acidity were also assessed. The delay in the onset of the climacteric rise in ethylene evolution shows enzymatic-type kinetics, with saturation levels of about 8-10% oxygen. Treatment with pure oxygen was highly detrimental; it induced visual symptoms of low-oxygen damage and high levels of ethanol. The slope of the rise in ethylene evolution is also a function of oxygen concentration, with an apparent Km for oxygen lower than that which delays the climacteric onset. The effect of oxygen on respiration is dependent on the physiological state of the fruit. In preclimacteric fruits, levels of oxygen between 2 and 8% eventually decrease respiration. Calculations of internal oxygen levels indicate that the diminution of respiration results from decreased metabolic activity in response to hypoxia.