Diffusive resistance and photosynthetic rate of leaves and root growth andactivity with emphasis on berry coloration in 'Pione' grapevines

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. Barry development, root growth and activity, and diffusive resistance and p hotosynthetic rates of leaves on each vine were recorded. Although leaf are a per shout, yield and cluster weight differed, the differences between the SEC and IBC vines were not significant. The index of skin coloration, base d on a color chart was significantly lower on IBC vines than that on SEC vi nes three weeks after veraison and during the ripening stage. At harvest, a nthocyanin content of berry skins in IBC vines was less than 50% of the SEC vines. Changes in color and/or anthocyanin lever of the skins closely corr elated to changes in total soluble solids contents of berries. In IBC leave s, the water saturation deficit remained low in spite of the low water cont ent 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 comparab le position on vine B, it was slightly slower. On vine C, a high photosynth etic rate was observed in the leaf only at the 7th node. One month after ve raison, leaves on only vine A maintained its high photosynthetic rate, irre spective of leaf position. Although they had a similar canopy area, the dry weight of IBC roots was lighter than that of SEC roots. White roots of SEC grew vigorously before veraison, whereas those of IBC began to grow three weeks after veraison. The total length of white and suberized roots was sho rter in IBC vines than in SEC vines. Three weeks after veraison, the activi ty of white root estimated from triphenyltetrazolium chloride (TTC) reducti on was significantly lower in vines of IBC than in that of SEC.