THE REGULATION OF SET AND DEVELOPMENT OF THE GRAPE BERRY

Grape flowers and berries react in diverse ways to growth substances, depending on the time of application. Pre-anthesis treatment with auxins causes premature growth of the ovule, while gibberellins inhibit seed growth. Gibberellins applied at or after anthesis promote pericarp growth mainly through cell enlargement. Seeds prevent this response. Auxins and ethylene applied during the slow-growth phase delay the onset of ripening, but ABA hastens it.

It is hypothesized that: (a) The hormonal control of the first rapid growth of the pericarp resides in interactions between auxins, cytokinins, gibberellins and abscisins and the relative importance of each changes as development progresses from cell division to cell enlargement. (b) The seed is the chief source of these hormones. (c) The second rapid growth phase is associated with ABA and sugar accumulation, initially in the skin.

For a period after anthesis the ovary appears to exert no control over the flow of organic nutrients to it. As a result, its abscission and early development are dependant on the overall supply of nutrients in the vine. Later, the berry develops an ability to attract nutrients and different limitations to accumulation then operate.