Effects of the Time Zone for Artificial Pollination on Fruit Set and Pollen Tube Growth of Sweet Cherry (Prunus avium L.)

Abstract

We investigated the effect of temperature change on pollen germination and pollen tube elongation in vitro, using the pollen of ‘Napoleon’ which is often used as a pollination tree. At two-stage variable temperatures, the elongation rate of the pollen tube decreased markedly immediately after changing the temperature from 20 to 4°C. Even when the temperature was returned to 20°C, the relative elongation of the pollen tube remained at 50% of the initial rate. Also, morphological abnormalities such as refraction and hypertrophy of the pollen tube tip were observed. When the temperature varied, germination was not observed, even after a lapse of 15 hours at 4°C. By changing the temperature to 20°C, the pollen tube elongated rapidly. The fruiting of sweet cherries depended on the temperature at the time of pollination. Good fruiting was achieved when pollination occurred between 10 a.m. and 2 p.m.; however, the fruiting rate was reduced with evening or early morning pollination when the temperature was lowered. When pollination occurred at 5 p.m., pollen tube extension was relatively favorable. However, morphological abnormalities in the pollen were observed.