Girdling or bark inversion of trunk, and shoot spraying of a growth retardant, SADH were applied to vigorous 5- and 6-year-old trees of Japanese persimmon var.
Saijo, and their effects on vegetative growth, flower formation and yield were compared for several years after treatments(Ex.1 and 2). As to girdling alone, the effects of its reapplication in the next year and of its width on them were also examined(Ex. 2 and 3). Further, the influences of binding up the girdled portion with the tape of polyvinyl chloride film on the regeneration of bark in the wound tissue and the formation of flowers in current shoots were studied(Ex.4) since the wound tissue was protected by the binding against decication in each girdling treatment of these experiments mentioned above.
1. The girdling of trunk with the width of 5mm applied in late June or early July significantly inhibited current shoot growth, and this tendency continued for several years since then. The treatment increased the number of flowers and the yield of fruits per tree remarkably in the next year, and the total yield for 3 years after the treatment reached an amount 3(Ex.1) or 1.5(Ex.2) times larger in the girdled trees than in non treated ones. Further, it tended to increase fruit size continuously for several years.
The additional application of trunk girdling in the next year increased flower number and yield for 2 years after the begining of treatment as compared with the single application in the first year. However, there was hardly any difference in total yield for 5 years between these two treatments as flower number per tree more decreased and the rate of physiological fruit drop became higher in the former treatment than in the latter in the third year.
No obvious difference was detected between the two girdling treatments with the widths of 5 and 10 mm in regard to shoot length, flower number and the contents of nitrogen and carbohydrates in leaves.
On the other hand, the binding of girdled portion with vinyl tape was found to be very effective for acceralating the regeneration of bark showing higher N and lower carbohydrate contents in leaves 1 and 2 months after the treatment than the girdling without the protection. And yet, both treatments exhibited the promotive effect on flower formation at almost the similar level.
2. Bark inversion with the width of 5 cm remaining a portion of bark intact at the rate of 1/10 of trunk circumference was approximately as effective as the girdling treatments with the widths of 5 and 10 mm for depressing shoot growth and increasing yield in the treated year and also for several years after then.
3. Shoot spraying with SADH at the concentration of 5000 ppm applied in late July showed no significant effect on shoot elongation including secondary growth and flower formation in the treated year and also yield in the next year.