The Development of Tomato Root System in Relation to the Carbohydrate Status of the Whole Plant

The decrease in growth rate of the root system or complete cessation of its growth in developed, fruit-bearing tomato plants are known phenomena. It has been suggested that a limited supply of carbohydrates to this organ, due to its relative weakness in competition with the flowers and developing fruitlets is the main cause for these disorders. This theory was tested in the present study with plants grown in an aerohydroponic system up to the appearance of 12–13 trusses per plant, 172 d after transplanting. The changes in the contents of carbohydrates in the various organs during this period were monitored. The concentrations of soluble sugars and starch in the leaves increased with the increase in truss number. The upper stem was found to contain more carbohydrates than the lower stem, while no significant changes in the concentration of these compounds could be detected in the roots throughout the experiment. Nevertheless, 120–130 d after transplanting, the roots of the plants, bearing five to six trusses and two to three inflorescences, ceased growing and remained at the same or a slightly reduced size for another 40–50 d. Calculations show that at the stage of five to six trusses, 38 g total soluble sugars and 35 g starch were stored in the vegetative organs. Therefore, it seems unlikely that carbon deficiency caused by the competition with the reproductive organs (mainly developing fruits), affected the root growth. Instead, it is suggested that some other factor is responsible.