Abstract
Four seedless 'Pione' grapevines, treated with gibberellic acid, which bore well-[vine A and B, superior berry coloration (SBC)] and poorly-[vine C and D, inferior berry coloration (IBC)] colored berries annually were studied. Berry development, root growth and activity, and diffusive resistance and photosynthetic rates of leaves on each vine were recorded. Although leaf area per shoot, yield and cluster weight differed, the differences between the SBC and IBC vines were not significant. The index of skin coloration, based on a color chart was significantly lower on IBC vines than that on SBC vines three weeks after veraison and during the ripening stage. At harvest, anthocyanin content of berry skins in IBC vines was less than 50% of the SBC vines. Changes in color and/or anthocyanin level of the skins closely correlated to changes in total soluble solids contents of berries. In IBC leaves, the water saturation deficit remained low in spite of the low water content after veraison, whereas the diffusive resistance tended to increase. At veraison, leaves at the 2nd and 7th nodes above a cluster borne on vine A exhibited a relatively high photosynthetic rate, whereas leaves at comparable position on vine B, it was slightly slower. On vine C, a high photosynthetic rate was observed in the leaf only at the 7th node. One month after veraison, leaves on only vine A maintained its high photosynthetic rate, irrespective of leaf position. Although they had a similar canopy area, the dry weight of IBC roots was lighter than that of SBC roots. White roots of SBC grew vigorously before veraison, whereas those of IBC began to grow three weeks after veraison. The total length of white and suberized roots was shorter in IBC vines than in SBC vines. Three weeks after veraison, the activity of white root estimated from triphenyltetrazolium chloride (TTC) reduction was significantly lower in vines of IBC than in that of SBC.
