Influence of untimely defoliation on the subsequent growth in some deciduous fruit trees. I

Abstract

1. The effect of defoliation on the vegetative growth and flower bud formation was observed with young potted peaches, variety Okayama-wase, by removing all the leaves artifically at certain intervals during the growing season from June to October in 1959.2. When all the leaves were removed, terminal and secondary leaf buds came out from the axils and developed into new shoots, except on the trees defoliated in October. The earlier the defoliation, the sooner and the more the buds sprouted. These shoots grew so late in autumn that the leaves fell 30 to 50 days later than usual. Accordingly, the buds on these shoots sprouted late irregularly and ununiformly in the following spring. This tendency was most conspicuous in the trees defoliated on August 7.3. No flower buds appeared both on the trees defoliated in June and July, and some flower-like buds in August. However, on the trees defoliated after September complete flower buds were formed. The earlier the time of defoliation, the more decreased the number of flower buds per tree and the more ununiform the flowering time in the following year. The trees defoliated in September bloomed in October of the treated year, and those defoliated in August bloomed most abnormally in the following year.4. While the shoot growth was generally well in the treated year except the trees defoliated in July, the growth of the following year was strikingly bad except those defoliated in October. Moreover, the defoliation in July and August retarded the root growth greatly.5. From the results obtained, it is evident that in the Okayama-wase peaches flower buds were formed completely in September. These flower buds were already in the rest period in mid to end of September and leaf buds in October. And so the trees defoliated untimely in previous growing season showed “prolonged dormancy”.