Effects of Exposing Satsuma Mandarin Trees Grown under Low Temperature Regimens in Winter and Early Spring on Flower Bud Development and Flowering

Abstract

One-year-old potted satsuma trees (cv. Okitsu Wase) on trifoliate orange were exposed to 0°, 5°, 10° and 15°C in growth chambers or to fluctuating temperatures under field conditions. The temperature treatments extended for 1 or 4 months between December to and including March. During this period the axillary buds were in a stage of ecodor-mancy but were differentiating flower buds. When the trees were not under treatment, they were kept at 10°C. All trees were transferred to the field on March 30, 1984. The time of floral flush, the cumulative number of flower buds and flowering time as well as sizes of flowers and ovaries collected at full bloom were observed for trees under each temperature regimen.
1. Flower buds on trees held at 15° and 10°C for 4 months appeared on mid-February and early March, respectively. Those on trees held in the field and at 0° and 5°C began to sprout on last April. Among trees treated for 1 month, the earlier the treatment, the earlier the sprouting time of flower buds.
2. Among trees treated for 4 months, the total number of flower buds was the largest on trees which were kept continuously in the field; it was the smallest on trees kept at 15°C. Of the trees treated for 1 month, that on trees held in the field in February decreased markedly, and in March decreased slightly for cold injury. One-month treatment in March at 0° and 5°C decreased flowers slightly.
3. Trees held for a 4-month period at 15°, 10°C and other treatments were in full bloom on mid-April, mid-May and last May, respectively. Dates of full bloom of trees kept at 0°, 5°C and in the field for 1 month were mid-May. Those of trees kept at 15°C were earlier as the temperature treatment treated later.
4. Sizes of flowers at full bloom were the greatest at 0°C and the smallest at 15°C for 4-month treatments. The ovaries were big at 15°C. Of trees treated for 1 month, flowers in the field were greater when the treatment were commenced later, but the ovaries were the greatest in February treatment. Later temperature treatments of 15°C produced smaller flowers with bigger ovaries.