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APPLE FRUIT GROWTH 

 Franklin VV. Southwick^ 



There is often some confusion about the growth of apples, particularly concerning 

 the year-to-year variation in fruit shape and the growth during the harvest season. 

 During and shortly after bloom apparently is a critical stage in fruit development 

 because fruit size is primarily due to cell number, and cell division ceases about 3 

 weeks after full bloom. Thus, an apple with a greater number of cells at bloom, or 

 shortly thereafter, has the potential to become larger in size by harvest than one with 

 fewer cells. 



Apple fruits increase in length and diameter after bloom. In 1914, J.R. Shaw in 

 Massachusetts reported on the relationship between shape of Ben Davis and Baldwin 

 apples and the temperature following bloom; the cooler the temperature, the more 

 elongated the apple. He concluded that during the post-bloom period, temperature 

 variations between the 6th and 16th day after full bloom fitted the observed variations 

 in shape more closely than did temperature variations during any other period. As 

 most growers know, distribution of seeds in fruit influences shape. Apples with a small 

 number of seeds are frequently lopsided, with the less fleshy side being the one lacking 

 seeds. The "king" fruit generally is larger than "side-bloom" fruit. 



From approximately 3 weeks following bloom to harvest fruit growth is by cell 

 enlargement. Figure 1 shows typical growth curves for Early Mcintosh and Golden 

 Delicious apples plotted on the basis of fruit diameter and volume (assuming the fruit 

 to be a perfect sphere). It can be noted that the growth rate is constant with no "final 

 swell". In fact, when one plots the growth curve on the basis of diameter it appears 

 that the rate of apple fruit growth tends to slow down as the fruit approaches maturity. 

 This apparent slackening of growth rate is more pronounced for the later maturing 

 Golden Delicious than for the earlier maturing Early Mcintosh. If the data are calculated 

 on the basis of volume increase, however, it is apparent that the growth rate actually 

 accelerates in July and may not taper off appreciably for early apples and only slightly 

 before harvest for late varieties. Thus, there is no periods of accelerated or decelerated 

 growth as with the stone fruits. Fruit volume increases rapidly as fruit become larger 

 because progressively more volume is required to add a given increment to the fruit 

 diameter. This is shown in Table I where it can be seen, for example, that an increase 

 in diameter of 0.1 inch on a 2.60 inch apple represents a volume increase of 18.51 cubic 

 centimeters as compared to a 17.19 cubic centimeter increase in volume of a 1.50 inch 

 apple that has grown another 0.25 inch in diameter. Also, a 0.25 inch increase on a 

 3.00 inch apple represents an increase in volume almost equivalent to the entire cubic 

 contents of a 2.00 inch apple. 



Since Mcintosh may grow at the rate of 0.07 to 0.10 inch in diameter per week 

 in September, the addition of 0.15 inch diameter on a 2.50 inch apple represents a 19.1 

 percent volume gain or a 17.2 percent increase in volume on a 2.75 apple within two 

 weeks. In other words, the delay in harvest of 2 weeks can add materially to the volume 

 of Mcintosh picked and to individual fruit size. 



^Professor Emeritus, Department of Plant and Soil Sciences 



