Effect of temperature during the first 42 days following full bloom on apple fruit growth and size at harvest

Abstract

The relationship between temperature prevailing during the 42-day period following full bloom (42 DFFB) and fruit size at harvest of four apple cultivars was studied for two seasons. Lower temperatures during the first season resulted in smaller fruit whereas higher temperatures the following season resulted in larger fruit at 42 DFFB. The smaller fruit size at 42 DFFB during the first season was related to lower temperatures during the first, fourth and fifth weeks following bloom. High rates of Starking fruit growth were associated with increased rates of cell division in the cortical region. The relationship between fruit size at 42 DFFB and fruit size at harvest was affected by the number of fruits per cm trunk circumference during the current and the previous season. The relationship between the average mass per fruit at harvest, number of fruits per cm trunk circumference during the current year, kg fruit per cm trunk circumference the previous year, average diameter of fruits at 42 DFFB and number of hours above 14°C until 42 DFFB was calculated for the seasons 1978/79 to 1981/82. A multiple linear regression equation of the form Y=b0+b1X1+b2X2+b3X3+b4X4 was fitted to the data. The number of fruits per cm trunk circumference during the current year was a dominant variable. Although higher temperatures improved the weekly rate of fruit growth during the first 42 DFFB, this effect was offset during most years by an increase in the number of fruits set per cm trunk circumference as a result of more favourable weather conditions during and immediatly after bloom.