Gibberellins are plant hormones that promote cell elongation and division, leading to increased fruit size. Their common applications include:
Increasing the size of grapes and apples.
Promoting stem elongation and seed germination.
Auxins and cytokinins also influence plant growth but are not specifically utilized for enhancing fruit size.
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Final Answer:
\[
\boxed{\text{Gibberellin}}
\]