Early post-veraison growth in grapes: evidence for a two-step mode of berry enlargement

An account is provided of berry softening plus cell wall loosening in flesh and skin tissues, that relates to changes in berry turgor and sugar accumulation around veraison in Golden Muscat (Vitis vinifera × V. labrusca). The onset of change in berry deformability was taken as a demarcation between pre-veraison and post-veraison growth phases. Our results confirmed that post-veraison berry enlargement was preceded by berry softening and sugar accumulation. Berry ‘turgor’ (as inferred from the rate of juice exudation from punctured fruit) increased abruptly and concurrently with berry softening and sugar accumulation, but dropped steadily with subsequent berry expansion. Elasticity of skin tissues decreased abruptly during early phases of expansion, while berry deformability increased. We suggest that cell wall loosening in flesh tissues precedes cell wall loosening in skin tissues, and that this loosening sequence results in a two step sequence where berry softening is later followed by berry expansion.