Abstract
The development of whole fruit diameter, mesocarp and seeds was analyzed from full bloom to maturation in six cultivars of Japanese apricot (Prunus mume Sieb. et Zucc.) with different fruit sizes. The radial length of mesocarp cells in the equatorial cross section was measured, and the number of mesocarp cells was estimated. The rate of mesocarp cell division and the final cell number index were compared among cultivars. The frequency of gummy fruits in these cultivars was determined, and the length of mesocarp cells at the fruit apex was measured. The relationship between these two values was examined. Cell division in 'Koshusaisho' (fruits < 6 g) ceased at 4 weeks after the full bloom, much earlier than in other cultivars. The final cell number index, 50 plus, was very small. In contrast, cell division in the mesocarp of 'Bungo (Hiratsuka)' (fruits > 60 g) continued for 50 days after anthesis, the longest period among the cultivars tested; its final cell number index reached about 140. In the other four cultivars, the final cell number indices ranged from 90 to 110. The number of mesocarp cells strongly effected the final fruit weight. There were clear varietal differences in the occurrence of gummy fruits. The percentages of fruits gumming at the apex were 50.0% in 'Getsusekai', 11.8% in 'Shirokaga' and 3.0% in 'Kagajizou'. A high correlation occurred between the radial length of mesocarp cells and the cell length in the fruit apex tissues, but the slopes of the regression lines varied among cultivars. These slopes and the frequency of gumming in the fruit apex were positively correlated which suggests that the development of the gumming syndrome in the fruit apex is attributable to the disproportionate in the apex. This leads to the formation of a gap between mesocarp and endocarp in which resinous substances subsequently accumulate.
