Effect of fruit load on partitioning of dry matter and energy in cantaloupe (Cucumis melo L.)

Cantaloupe (Cucumis melo L.) plants set groups of fruits which generate lar ge variations in the reproductive: vegetative dry weight balance. We studie d the influence of fruit number on the partitioning of dry matter and energ y between the vegetative and reproductive organs and among the seeds and th e various fruit tissues during the development of the first fruits. Over 2 years and on two Charentais cantaloupe cultivars, fruit number was either l imited to one or left unrestricted, which led to the setting of two to six fruits. Because of the high lipid content in seeds, the distribution of ass imilates was studied in terms of energy equivalent as well as dry weight. M easured dry weights were converted into energy equivalents by calculating t he construction cost of tissues from their elemental composition. Seeds dif fered from other tissues in showing an increase in construction cost, from 1.1 to 1.8 g CH2O g(-1) d. wt between 10 and 30 d after pollination. For th is reason, during the second half of fruit development on plants with unres tricted fruit load, they made up to 31% of the fruit and 12% of the aerial part of the whole plant in terms of dry weight, but 39 and 18% in terms of energy (glucose equivalents). The fraction of assimilates allocated to the fruits showed a saturation-type response to the number of fruits per plant. It did not increase in cultivar Talma above two fruits per plant, which co uld be due to a decreasing sink strength with fruit rank, whereas cultivar Galoubet maintained a more homogeneous fruit size within plants. At a simil ar fruit load, the reproductive: vegetative dry weight balance differed bet ween the 2 years of the experiment, probably because of variation in the fr uit sink strength. (C) 1999 Annals of Botany Company.