High temperature rather than drought stress is responsible for the occurrence of double pistils in `Satohnishiki' sweet cherry

Abstract

Effects of temperature and soil moisture level on the occurrence of double pistils in `Satohnishiki' sweet cherry were studied. Trees were grown in sunlit growth chambers controlled at 25°C/25°C, 30°C/25°C and 35°C/25°C, day/night from late July to early September. The higher the temperature, the slower the progression of flower differentiation. At 25°C, all the flower buds had a single pistil, whereas above 30°C, the percentage of flowers with double pistils increased remarkably. More than 80% of the flowers differentiated double pistils at 35°C and some had triple pistils. In another experiment, trees were grown under moist [soil moisture tension (SMT) <6 kPa] and dry (SMT < 32 kPa) conditions in chambers controlled at 25°C/15°C and 35°C/25°C. Though the trees did not show symptoms of water stress under the low temperature/moist soil regime, the leaf water potential under the high temperature/moist soil regime decreased to almost the same level as that under both dry soil regimes. At high temperatures, the occurrence of double pistils was severe. However, the soil moisture did not affect appreciably the frequency. In contrast, pistil doubling was not observed at low temperatures at all. Under field conditions, by the restriction of watering, the leaf water potential obviously decreased. However, the frequency of occurrence of double pistils under the dry soil regime (SMT < 51 kPa) was not higher than that under the moist soil regime (SMT < 13 kPa). These results suggested that high temperature above 30°C is a critical factor in the formation of double pistils in `Satohnishiki' sweet cherry.