13C-labelling of leaf photoassimilates to study the source–sink relationship in two Iranian melon cultivars

To study the effect of fruit position on the stem on photoassimilate partitioning in two Iranian melon cultivars (Suski-Sabz and Jalali-Zard), a greenhouse experiment was conducted. Three fruit positions (retaining one fruit on 3rd, 7th or 11th node of two lateral branches) and three leaf positions for 13C-labelling (3rd, 8th or 12th leaf from the base of one branch) were compared during the experiment. Results showed that the time at which the maximum photosynthesis rate occurred in selected leaves was different according to leaf rank and this can affect the role and share of a given leaf in fruit feeding. Labelling data indicated that fruits retained on the 7th node import higher photoassimilates (13C-labelled) than the others and that the adjacent or nearer leaves have more important role in a given fruit feeding. These results could explain why experienced Iranian melon producers believe thinning (removing all female flowers before and after 6th–8th nodes of each lateral branch) results in largest fruits and the best quality.

► We examine the role of leaf ranks on feeding a given fruit in two melon cultivars.
► We use 13C-labelling of photoassimilates to determine which fruit does receive more label.
► We show that the adjacent leaves have a more important role in feeding a given fruit.
► The fruit retained on the 7th node receives the highest label whatever the leaf rank labelled.