EFFECT OF FRUIT-GROWTH, TEMPERATURE AND IRRADIANCE ON BIOMASS ALLOCATION TO THE VEGETATIVE PARTS OF CUCUMBER

Cucumber plants were grown at 18 or 25-degrees-C with four intensities of fruit removal or at three different levels of irradiance in order to analyse the effects of fruit growth, temperature and irradiance on the dry matter allocation to leaves, stems, petioles and roots. With i ncreasing irradiance the dry weight of the vegetative part of the shoo t increased, but the proportion of the total dry matter distributed to this part decreased. An increase in irradiance enhanced stem dry matt er production less than leaf and petiole dry matter production which w as in turn less stimulated than root dry matter production. In fruit b earing plants an increase in temperature had no effect on the dry matt er allocation to the leaves, stems and petioles, but reduced the alloc ation to the roots. Fruit growth strongly reduced dry matter productio n of all vegetative plant parts, but the distribution between stems, l eaves and petioles was only slightly affected. At 25-degrees-C the dry matter distribution between the roots and the vegetative part of the shoot was not affected by fruit growth but at 18-degrees-C the weight ratio of root to vegetative shoot part decreased with increasing numbe r of fruits on the plant. The biomass allocation between roots and sho ot is discussed in relation to the functional equilibrium concept.