Studies of fruit growth and fruit set with peach and apple indicate that the fruit which remain on the plant to harvest are those which maintain their growth rates all season long. The fruit that drop, especially early in the season, are those whose growth falls to very low rates for several days. Although this has not been examined in all fruit, it appears that, in these species, adequate fruit growth is needed not only to achieve optimum final size but also to increase number of fruit remaining to harvest (and thus the yield potential).
Fruit growth can be limited by several factors. First, most fruit crops produce many more flowers than the plants can support to maturity. There is natural drop of many fruit, but without grower intervention, tree fruit will still produce an overly large crop of very small fruit. The numerous fruit compete for limited resources from the tree (probably carbohydrates or nitrogen), and consequently fruit growth is inhibited. This is especially critical during the early cell division period. If competition can be limited by reducing the number of fruit at this time, final fruit size will be improved. Because of this response, considerable research is devoted to developing procedures for thinning fruit (reduction of fruit numbers to increase size). Thinning is a common and critical practice in production of most temperate tree fruit crops.
Besides competition among fruit on the same plant, there may be many environmental limitations to fruit growth. The most obvious is temperature. Fruit growth in the early season during cell division appears to be quite sensitive to temperature, similar to many growth processes. However, once fruit begin to grow by cell expansion, fruit growth rates appear to be much less influenced by temperature. Reduced light availability, during dark, cloudy periods or by shade within a plant interior, also limits fruit growth, especially in the early season. This effect appears to result from reduced availability of carbohydrates to fruit. Low light can cause a dramatic reduction in fruit set, particularly if there is a heavy crop on the plants at the time. In addition, any resource limitation such as drought stress or nutrient deficiency can limit fruit growth, just as it limits all forms of plant growth (shoots, roots, etc.).
Was this article helpful?