In order to find out the suitable rootstock for Delaware grapes grown in clayey soil areas, a comparative study has been conducted since 1964 on Delaware grapevines approach-grafted with seven phylloxera-resistant rootstocks in the vineyard of Shimane University, Honjo, Matsue. The rootstocks used were Hybrid Franc (V. rupestris x V. vinifera), 1202 ( V. mourvedre × V. rupestris), 3306 ( V. riparia × V. rupestris), 3309 ( V. riparta × V. rupestris) , 420A ( V. berlandieri × V. riparia), Teleki 8B ( V. berlandieri × V riparia), and Teleki 5BB ( V. berlandieri × V. riparia). This report involves the results obtained in initial 5 years until 1969.
As for yield, Delaware grapevines grafted on the rootstocks of 3309, 3306 and Hybrid Franc were the most superior, followed by that on Teleki 8B, own-rooted, on 420A, Teleki 5BB, and 1202 in the order. These differences in the productivity of the scion variety were closely related to the size of canopy, which was affected extremely by the rootstocks. The rootstocks of 3309, 3306 and Hybrid Franc also had good effects on bunch size as well as berry size, and 3309 was the best in the respects of qualitative charactors of bunch such as skin color and the contents of soluble solids and free acids. Among the contents of N, P, K, Ca and Mg in the leaves, N content was most fluctuated by the rootstocks, but any distinctive relationship could not be found between N content and growth or yield in the grafted vines.
Thus, 3309, 3306 and Hybrid Franc, especially 3309 seem to be the favorable rootstocks for Delaware grapes in the soil condition at this time, though further long term study is necessary to come to the final conclusion.