THE DEVELOPMENT OF TOMATO ROOT-SYSTEM IN RELATION TO THE CARBOHYDRATESTATUS OF THE WHOLE-PLANT

The decrease in growth rate of the root system or complete cessation o f its growth in developed, fruit-bearing tomato plants are known pheno mena. It has been suggested that a limited supply of carbohydrates to this organ, due to its relative weakness in competition with the flowe rs and developing fruitlets is the main cause for these disorders. Thi s theory was tested in the present study with plants grown in an aeroh ydroponic 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 concentrati ons of soluble sugars and starch in the leaves increased with the incr ease in truss number. The upper stem was found to contain more carbohy drates than the lower stem, while no significant changes in the concen tration of these compounds could be detected in the roots throughout t he experiment. Nevertheless, 120-130 d after transplanting, the roots of the plants, bearing five to six trusses and two to three infloresce nces, ceased growing and remained at the same or a slightly reduced si ze 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 defic iency caused by the competition with the reproductive organs (mainly d eveloping fruits), affected the root growth. Instead, it is suggested that some other factor is responsible. (C) 1997 Annals of Botany Compa ny.