PHOTOSYNTHETIC CONTROL FACTORS IN A SINGLE LEAF OF SWEET-POTATO, IPOMOEA-BATATAS LAM .2. SINK-SOURCE RELATIONSHIP BETWEEN PHOTOSYNTHESIS AND ROOT WEIGHT PRODUCTION IN SINGLE LEAF GRAFTS

Photosynthesis and root weight production in single leaf grafts were discussed from the point of view of sink-source balance. Cultivars used were Koganesengan (K), Siroyutaka (S), Beniaka (B) and Tsurunasigenji (T). Scion (leaf+petiole) and stock (petiole+roots) of the four cultivars were reciprocally grafted in 16 combinations. To elucidate the single and compound effects of sink and source on root weight (R(X/Y)), mathematical models were derived, from which scion effect (E(X/*)), stock effect (E*/Y) and their combination effects, general combining effect (GCE(X/Y)) and specific combining effect (SCE(X/Y)), were calculated. The relationships of these components were shown as the following equations. R(X/*)=E(X/*) +R*/* ; R*/Y=E*/Y +R*/* ; GCE(X/Y)=(E(X/*) +E*/Y)/2; R(X/Y)=GCE(X/Y) +SCE(X/Y) +R*/* : where R(X/*) and R*/Y are the average root weights of the grafts with cv. (X) scion and cv. (Y) stock, respectively. R(X/Y) is the root weight of a graft with cv. (X) scion and cv. (Y) stock. R*/* is the average root weight of all the plants of 16 graft combinations. When K or B was used as scion, the root weight of grafted plants highly increased; the scion effects of both cultivars were positive. Also the stock effect of K was positive. While both scion and stock effects of T were negative and the lowest. A positive linear relationship was detected between GCE and SCE, but T/S and T/B were excepted from the tendency. Photosynthetic rate increased in the plants grafted to K-scion or K-stock, while in T/S and T/T the rates significantly reduced. Root weight production was positively related to photosynthetic rate within a limited range.In T/S and the grafts with T-stock, peitole weights increased; the petiole functioned as a sink when the tuber sink capacity was limited.