Effect of Source-Sink Balance on Hormone content and Fruit Size of Greenhouse tomato

Regulation of fruit size is a major issue in higher plant development, and an economic factor for many horticultural crops, consist of tomato. Under non-limiting environmental factors of photosynthesis, fruit size is mainly restricted by the number of fruits per plant or sink-source balance because of difference in sink strength or in other words the competitive ability of a sink organ to attract assimilates. Therefore, the present study was undertaken to investigate the effect of the sink-source balance in determining the size of individual fruits at the different developmental stages of greenhouse tomato cultivar ‘Grandella’. To this end, a split-plot factorial experiment was conducted based on a completely randomized design with three replications. Two treatments were applied: saving one fruit per truss (۱F), and no fruit pruning (control). Three developmental stages of tomato fruit including cell division (۱۵-day after treatment; DAT), cell expansion (۳۰-DAT), and ripening (۴۵-DAT) were studied. The auxin and cytokinin content of fruits was measured using high-performance liquid chromatography (HPLC). The results showed that fruit thinning could increase auxin and cytokinin concentrations. Fruit weight and pericarp thickness were determined by sink-source balance. Similar patterns of auxin, and cytokinin concentrations, pericarp thickness, and fruit weight during developmental stages of tomato fruits suggested the controlling role of auxin and cytokinin in determining fruit size by regulating cell division, cell expansion, and mobilization of photoassimilates. Based on the results of the present study, applying fruit thinning and limiting the number of fruits per truss, decreased competition in the truss and had a positive effect on the sink strength of individual fruit per truss, so we can conduct that auxin and cytokinin are involved in growth processes or regulation of sink strength in fruits.

Keywords:

Auxin , Cytokinin , Fruit weight , Pericarp thickness , sink strength