Characteristics of Berry Growth during Stage II, and the Components of “Speck” Disorder in ‘Muscat of Alexandria’ Grape

Abstract

The characteristics of berry growth during Stage II of ‘Muscat of Alexandria’ grape were investigated, since “Speck” symptom of the berry disorder is mainly developed in this period.
1. The daily increment of berry diameter was smallest in the Stage II of all devel-oping stages, about 40 to 60 days after blooming. Percentages of dry matter of berries were also lowest in this period, while water content was highest. As for berry firmness measured by a tensile tester, when the rate of berry deformation was calculated by the narrowed diameter just before crushing, it was lowest at about 40 days after blooming. It increased gradually to veraison, and reached a plateau at ripening after a rapid increase. But the loading weight required for crushing the berries increased gradually from Stage I to veraison, and decreased thereafter.
2. During Stage II, the berry diameter measured by eddy sensors began to increase rapidly at around 4 a.m. and reached its maximum at around 10 a.m., then decreased toward evening, and was restored to the original size by midnight. Berry firmness was lower during the time from midnight to early morning and lowest at around 6 a.m., accompanied by the changes in osmotic potential of the juice.
3. Diurnal changes in the rate of appearance of “Speck” symptoms were also recognized. Although the changes occasionally fluctuated with conditions, the symptoms mainly appeared at 4 a.m., with a peak at around 6 a.m., when the water potential of the berries was highest.
4. As microscopic observation of “Speck” has shown that the peripheral vascular bundles were partially necrosed and the adjacent parenchyma tissues were broken down, “Speck” is supposed to occur with the following causes: 1) the increased pressure of sap ascending from evening to early morning may destroy the pericarp tissues closed to the broken vascular bundles, 2) the destroyed tissues are aggregated by the diurnal changes in water potential, and 3) this sequence results in a cavity.