Decreased RNase Activity Under High Temperature Is Related to Promotion of Self-pollen Tube Growth in the Pistil of the Japanese Flowering Cherry, Prunus x yedoensis 'Somei-yoshino'

Prunus x yedoensis Matsum. 'Somei-yoshino' is one of the most popular flowering cherry cultivars in Japan. However, because flowering cherries have strict self-incompatibility (SI), it is difficult to develop selfing families or inbred lines for breeding and genetic studies. SI in Prunus is achieved through arrest of self-pollen tube growth in the style by ribonuclease S-RNase. To determine a suitable way to overcome SI in Prunus, we examined the influence of hot water immersion on RNase activity in the style of 'Somei-yoshino'. When the styles were immersed in 20 degrees C, 30 degrees C, and 40 degrees C water baths, their RNase activity was not significantly different from that of untreated styles (P > 0.05); however, it significantly decreased in styles heated in 50 degrees C water baths (P < 0.01). Furthermore, the RNase activity decreased with an increase in the incubation time (e.g., 1, 3, and 5 min). Additionally, heat treatment at 50 degrees C promoted the growth of self-pollen tubes in the style. Some self-pollen tubes even reached the bottom of the style. The high temperature treatment with reduced RNase activity can overcome stylar SI in Prunus.