TOMATO (LYCOPERSICON-ESCULENTUM MILL, CV BETTER BUSH) PLANT-RESPONSE TO ROOT RESTRICTION .1. ALTERATION OF PLANT MORPHOLOGY

Observations presented here describe changes in the growth of Lycopersicon esculentum Mill., cv. 'Better Bush', at the onset of root-restriction stress. Plants were grown in either 1500 cm3 (control) or 25 cm3 (treated) containers in a flow-through hydroponic culture system (FTS). Seeds were imbibed, germinated, held for 13 d in sterile germination bags, then placed into the FTS and designated day zero plants. Plants grown in the FTS were harvested, every 7 d, from day 11 to day 46. Plant height, root and shoot weights, leaf areas, leaf lengths, branching and flowering were measured to illustrate morphological changes that occurred in response to root-restriction stress. Plants restricted to a 25 cm3 root volume experienced a marked stress after 18 d in the FTS. A reduction in leaf elongation was evident and preceded the time (prior to day 25) when maximum dry weights were attained by restricted root systems. Control plants had greater leaf areas and plant dry weights than those of root-restricted plants after day 18. Treated plants showed no significant increase in dry weights from day 32 to the end of the experiment. Between day 18 and 25 the root: shoot ratio for the treated plants dropped below that of the controls. Adventitious rooting was evident in treated plants by day 25. Roots of the treated plants showed an apparent waterlogging indicated by browning of roots by day 32. Root turnover followed as the primary root system was replaced by adventitious roots. The number of branches or flowers did not differ between control and treated plants. The timing of the events described here can be used to further the study of specific physiological responses of tomato plants to root-restriction stress.