Studies on dwarfing mechanisms of dwarf rootstocks

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Accurate evaluation of the dwarfing ability of rootstocks at the seedling stage permits faster progress in breeding programs for the dwarf rootstocks. The objective of this study was to determine whether callus from a dwarfing rootstock restricted growth of another callus from a scion cultivar in vitro as would be expected from a field performance. Calli were derived from shoots of peach and Prunus japonica Thunb. These calli were grown in scion-stock position, placing filter paper between them. Peach callus in the stock position, i.e. grown in contact with the media, weighed less when grown under P.japonica callus than when grown under peach callus. P.japonica callus in the scion position weighed more when grown on peach callus. Peach callus in the scion position grew equally well on either peach or P.japonica callus. In another experiment, peach callus was transferred into the media where P.japonica callus was previously incubated for one week and then removed. Peach callus weighed less on the media previously incubated with P.japonica. Preincubation of peach callus did not affect growth of P.japanica callus. When peach and P.japonica calli were placed in the adjacent position without contact, one kind of callus did not affect growth of callus adjacent to it.P.japonica contained nore phenols than peach, but growth of peach callus was independent of phenol contents of P.japonica and itself. The results suggest that dwarfing ability of rootstocks couldbe evaluated by tissue culture techniques and that dwarfing is caused by some compounds released from P.japonica.