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The physiology of flower and fruitlet drop in apples

The physiology of flower and fruitlet drop in apples

The natural abscission (drop) of flowers and fruits

Fruitlets were traditionally thought to drop off in response to the death of their seeds (embryos) and the cessation of the supply of auxins from the live seeds across the abscission zone in the fruit stalk.

  • Although embryo death possibly explains a significant proportion of natural fruitlet abscission, [hyperlink 18] it does not explain it all.
  • Fallen fruitlets can often be found which have live plump seeds within them.
  • Also, research has failed to explain conclusively the causes of the embryo abortion itself.

Hormones occurring naturally within the tree that are associated with flower and fruitlet abscission

  • Several natural plant hormones [hyperlink 19] have been implicated in the tree processes leading to flower and/or fruitlet abscission (drop), particularly auxins and ethylene.

Application of plant growth regulators to induce flower and fruitlet abscission

  • Various chemicals [hyperlink 20] have been shown to have thinning action when sprayed onto apple trees including, auxins, carbaryl, ethylene releasing chemicals, photosynthesis inhibiting chemicals and cytokinins (benzyl adenine – BA).
  • Recent studies have shown that jasmonic acid and n-propyl dihydrojasmonate (PDJ) may have potential as a fruitlet thinner in certain fruit crops (Fujisawa et al., 1997) see Further reading [hyperlink]).