Double-working of Satsuma orange. II

A strain of Satsuma orange (Citrus unshiu) was rebudded on three different strains of Satsuma oranges, Yuzu (C. junos), and Tachibana (C. tachibana) in September, 1939. These interstocks had been budded on trifoliate orange (Poucirus trifoliata) rootstocks in September, 1937. The scion was the same strain as one of the interstocks of Satsuma. In April, 1959, these double-worked trees were all dug out and every part of them was weighed. The effects of the interstocks on the tree growth, fruit quality and yields for the ten years after the previous report were investigated. The results of the present experiments are summarized as follows: 1. The interstock of a dwarf Satsuma strain (Nods) showed less vigor of the top, less yield, and less growth of rootstock than those of a vigorous one (Tanikawa). These tendencies have become more conspicuous as the age of tree increased. 2. The tree growth and yield on the interstocks of the Satsuma strains other than the one used as the scion were less than those of the trees on Satsuma interstock of the same strain as the scion. 3. The Satsuma top on Tachibana interstock showed rather vigorous growth and larger cropping, while that on Yuzu interstock showed the poorest growth and the least cropping, and the trifoliata stock in this combination also showed very poor growth. The older the trees the more differences there were. 4. There were hardly any differences among the plants with different interstocks in the size, the coloring time, and the quality of fruit, excepting that plants with Yuzu interstock produced somewhat small fruits. 5. It was shown that the scion and the interstock had united well and the united part had uniformly grown on the interstock of three Satsuma strains. However, a marked swelling at the base of scion was seen on Tachibana interstock, while the scion on Yuzu interstock was more slender than the interstock itself. 6. When the bark of the trunk was removed, the woody tissue of Noda strain (one of the Satsuma interstocks) showed a distinct fissure at the bud union between the interstock and the rootstock, and then, the fissure splitted rather deep as the wood dried up. The other four interstocks showed no distinct symptoms at the bud union, although a marked overgrowth of the trifoliata rootstock had been seen in all tested trees, as usual. 7. All the interstocks of Tachibana and some of Yuzu showed a distinct stem-pitting like the symptom of tristeza at the part of interstock, but it was supposed to have no direct relation with the vigor of the tree.