Effects of Deficit Irrigation Strategies on Vine Water Status, Canopy and Cluster Temperatures, Fruit Total Phenolics,　and the Color of Muscat of Alexandria Table Grapes

　Effects of different deficit irrigation strategies on vine water status, canopy and cluster temperatures, fruit total phenolics, and the color of white table grapes (Vitis vinifera L., cv. Muscat of Alexandria) were compared to a well-irrigated control in 2004 from veraison to harvest at the Okayama University Experimental Vineyard, Japan. The treatments included: (1) well-irrigated control: re-irrigation when the soil moisture tension reached 15 kPa; (2) regulated deficit irrigation (RDI): re-irrigation 4 to 7 days after reaching a soil moisture tension of 15 kPa; (3) fixed partial root-zone wetting (FPRW): one part of the root system was re-irrigated when the soil moisture tension reached 15 kPa; and (4) alternate partial root-zone wetting (APRW): one part of the root system was re-irrigated when the soil moisture tension reached 15 kPa, and every week the irrigated part was switched. As the stress developed in RDI vines, leaf water potential and transpiration rate decreased and canopy and cluster temperatures increased as compared with the control. In contrast, both FPRW and APRW vines had similar leaf water potential and canopy and cluster temperatures, but less leaf transpiration rate as compared with the control. At harvest, fruits from all treatments had higher skin total phenolics and CIELAB a＊ values than the control. RDI fruit had higher total soluble solids (TSS), a similar acidity, and smaller size compared with the control. FPRW and APRW fruits had slightly higher TSS, lower acidity, and a similar size compared with the control.

ベレゾーン期から収穫期までの潅水制限処理が‘マスカット・オブ・アレキサンドリア’ブドウ（Vitis vinifera L｡）の水分条件，葉温，果実温，果実の全フェノール，果皮色に及ぼす影響を，十分に潅水した樹と比較した．実験は2004年に岡山大学農学部内の実験圃場で行った．処理区は，１) 土壌水分張力が15kPa に達したときに潅水する対照区，２) 土壌水分張力が15kPa に達してから４～７日後に潅水する制限潅水区，３) 土壌水分張力が15kPa に達したときに根域の半分に潅水する片側潅水区，４) 片側潅水する根域部分を１週間ごとに変更する交互潅水区とした．制限潅水区では水分ストレスが強まるにつれて葉の水ポテンシャルと蒸散速度が対照区よりも低下し，果実温が高くなった．しかし，片側潅水区と交互潅水区では，葉の水ポテンシャルと葉温，果実温は対照区と同程度で，蒸散速度が低下した．収穫期の果皮の全フェノールと CIELAB a＊ 値は，潅水を制限した各区では標準区より高かった．制限潅水区の果実は，標準区より糖度が高く，酸度は低く，果粒は小さかった．片側潅水区，交互潅水区では糖度がやや高く，酸度は低く，果粒の大きさは同程度であった．