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During the 1999 season, changes in total soluble solids (TSS), titratable acids (TA), pedicel diameter, berry diame­ ter, berry mass and fruit removal force (FRF) were determined at biweekly intervals from 27 until 111 days after full bloom (DAFB) for Waltham Cross table grapes. In addition, at each assessment stage, grape bunches were detached and held in the dark at about 25°C for SO h. Thereafter, moisture loss, FRF, berry abscission potential as well as percentage berry abscission were determined. During stages I and II of fruit growth (27 to 54 DAFB), TSS did not change significantly, while TA increased. FRF increased significantly during this early stage of berry devel­ opment, indicating a strengthening of the abscission zone tissue. During stage ill (after 54 DAFB), a decline in FRF occurred, which coincided with a perceptible increase in TSS and a decrease in TA. Berry mass increased signifi­ cantly from 27 to 111 DAFB. Pedicel diameter only increased significantly for the period 27 to 41 DAFB, while berry diameter increased significantly for the period 27 to 97 DAFB. Grapes sampled at 27 DAFB had a significantly lower FRF and significantly higher levels of berry abscission and moisture loss after the SO-hour period in the dark, compared with grapes sampled at a later stage. At 27 DAFB, the abscission zone developed between the pedicel and the rachis, thereafter it developed between the pedicel and the berry. Although FRF did not change significantly as berries ripened (from 83 to 111 DAFB), abscission potential and percentage berry abscission were significantly higher for grapes harvested at S3 DAFB at a TSS of 12.3°Brix than for grapes harvested more mature, at a higher TSS. Moisture loss correlated significantly (P<0.0001) with berry abscission, with a correlation coefficient of 0.S4. Berry abscission also correlated significantly (P<0.0001) with abscission potential, pedicel and berry diameter, FRF (at sampling), FRF (after SO h) and berry mass, but not with TSS or TA. The numerous physiological and biochemical changes that occur during grape berry (Vitis vinifera L.) development have been sub­ divided into three growth stages (Coombe, 1973). The duration and manifestation of each growth stage varies according to culti­ var and environmental conditions. Stage I is characterised by a rapid increase in berry size, firstly due to cell division, followed by cell enlargement (Coombe, 1976). During stage I, chlorophyll is the predominant pigment and berries display active metabolism, with high rates of respiration and rapid acid accumulation (Winkler et al., 1974). The levels of sugars remain almost constant and berries remain firm. Stage II is a slow growth phase during which the chlorophyll content decreases and maximum acid levels are attained. Stage ill extends from the beginning of ripening until the grapes are fully ripe, and is characterised by a sudden change in appearance and composition of the berries. During this stage there is an acceleration of berry growth, a decrease in berry firm­ ness and an increase in deformability, as well as an increase in glu­ cose and fructose contents (Coombe, 1973). Furthermore, decreas­ es in the concentration of organic acids, loss of chlorophyll from the skin, accumulation of anthocyanins and a decrease in respira­ tion rate take place during stage ill (Winkler et al., 1974).

Berry Abscission in Vitis vinifera L. cv. Waltham Cross: Changes in Abscission-related Factors during Berry Development