Effects of air and soil temperatures on flower development and morphology of satsuma mandarin

Three experiments were conducted in growth chambers to observe effects of air and soil temperatures in early and mid-winter on flower development and morphology of satsuma mandarin (Citrus unshiu Marc. cv. Okitsu Wase) budded on trifoliate orange. Four year old trees were used in Experiments I and III, and one year old ones in Experiment II. In Experiments I and II, air and soil temperature treatments of 15/15, 15/30, 30/15 and 30/ 30°C were started on 16 December, 1988. The trees sprouted flowers within seven days at 30/30°C, 11 days at 30/15°C, 21 days at 15/30°C, and 33 days at 15/15°C, respectively. There were few flowers at 30/30°C, extremely few at 30/15°C and many at both 15/15°C and 15/30°C. The days required to flowering and the flowering period were longer at the low air temperature. The number of flowers per tree, the number of flowers per node and the sprouting rate were greater at the low air temperature. A combination temperature of 30/15°C greatly decreased sprouting rate, the number of flowers per node and the number of flowers per tree. It seems likely that the chilling requirement might not be satisfied by mid-December. The trees might continue to accumulate chilling temperature at 15°C in the growth chamber. The trees at the high air temperature developed smaller flowers and ovaries. At an air temperature of 15°C, higher soil temperature resulted in bigger flowers and ovaries. In Experiment III, temperature treatments of 25/15,25/25 and 25/30°C were imposed on 6 January, 1989. The trees at 25/15°C required longer days to sprout and to blossom than at 25/25 and 25/30°C. The last two treatments did not differ in their effects. Soil temperature treatments did not result in significant effects on flower morphology, when they were applied after the chilling requirement was satisfied.