GROWTH DYNAMICS OF THE COTTON PLANT DURING WATER-DEFICIT STRESS

Information on the differential growth response of roots and shoots to water-deficit stress will better describe root growth within the soil for purposes of modeling plant growth and assessment of drought resistant traits. Our aim was to investigate leaf expansion and changes in root elongation for field and growth-chamber cotton (Gossypium hirsutum L.) during drought. Plants were grown in rhizotron containers and subjected to 6 d of water-deficit stress followed by 6 d of recovery and compared with a well-watered control. The stress period commenced when the plants were 55 to 65 d old. Leaf expansion was more sensitive to stress than root elongation, with curtailed growth after 2 d of with-holding water compared with 6 d with roots. Stress reduced root elongation and root volume. About 85% of visible roots showed elongation growth under conditions of adequate water, which was reduced by stress to 50%. Small (0.30 mm mean diam.) roots were more abundant and gave the greatest cumulative length, but grew less on a mean length basis than medium roots (0.62 mm mean diam.). The rate of root growth increased during recovery, consisting of regrowth from stalled roots and followed later by initiation of new roots. Medium roots contributed the most to root volume initiated during recovery. Most growth for both root sizes occurred in the lower zone of the soil, where water was more available. Root size and position of roots within the soil profile are important factors to consider when studying root growth response to water-deficit stress.