EFFECT OF ASSIMILATE SUPPLY ON THE GROWTH OF INDIVIDUAL CUCUMBER FRUITS

The effects of assimilate supply on the growth of individual fruits during different stages of fruit development were analysed in cucumber (Cucumis sativus L. cv. Corona). The assimilate supply was varied by maintaining different numbers of fruits per plant or maintaining different irradiances. The growth rate of a cucumber fruit strongly increased with increasing assimilate supply, but its growing period was not noticeably affected. At a low assimilate supply both cell number and cell size were reduced. Increasing the assimilate supply at different stages of fruit development showed that the early development of a cucumber fruit was not crucial for setting its growth potential. A small number of cells, due to a low assimilate supply during early fruit development, was to a great extent compensated by an increased expansion rate of individual cells. It is concluded that cell number is not an important determinant of fruit size in cucumber, although fruit size is often positively correlated with cell number. In the early stages of fruit development the effect of irradiance on the fruit growth rate depends on the presence of an earlier developed fruit because of dominance between fruits. In later stages of fruit development, a decrease in irradiance reduced the growth rate of all fruits relatively to the same extent independent of age or presence of other fruits.