Source activity evaluation by grafted leaves in sweet potato (Ipomoea batatas Lam.) cultivars.

The cultivaral feature and difference in leaf source activity were evaluated by using two-leaf grafts (plantlets with two grafted leaves) of sweet potato (Ipomoea batatas Lam.) cultivars. Two cultivars, Koganesengan ([K]) and Tsurunashigenji ([T]), characterized by high and low abilities in leaf photosynthesis, respectively, were used as experimental materials. A plantlet with two [K] leaves grafted onto the stock of [T] was described here as [K+K]/[T]. Using the grafts with six combinations of [K+K]/[T], [K+K]/[K], [T+T]/[T], [T+T]/[K], [K+T]/[T] and [K+T]/[K], the leaf photosynthetic rate (Pn) and leaf area (LA) were measured and compared between these combinations. Pn and LA in both cultivars increased in the grafts with [K] stock. When compared between leaves of [K] and [T] grafted to the same stock, higher values were obtained in both parameters in [K] leaves. The source activity (SOA; a product of Pn x LA) in [K] leaves showed two to three times higher than that of [T] leaves. This fact suggests that the cultivaral differences in both Pn and LA are more clearly observed when two leaves are placed under competitive conditions by grafting. The two-leaf graft employed here was proved to be useful as a test plant for evaluating the photosynthetic potential and its cultivaral feature in a single leaf of sweet potato.