Development of sorghum root system under increasing drought stress.

Sorghum (Sorghum bicolor Moench) plants were subjected to increasing drought stress condition for a period from 12 to 21 days after sowing and were compared with well-watered plants at different stages of growth in terms of root development. Droughted plants continued to produce new nodal roots (NR) and NR laterals with time but their number were consistently lesser than that of the control. Seminal root (SR) first-order lateral production was soon arrested by drought and notable reduction followed. Total length of NRs and NR first-order laterals per plant increased with time but at later stages increases were largely due to the presence of newly emerged roots that grew to some degree. Total length of SR first-order laterals was also depressed by drought. The rates of root production and root elongation of each component were generally suppressed by drought stress. Drought also caused marked reduction in the viability of root tips and root cortex. A profound decrease in viable root tips was also noted in all component roots of the control plants but this happened during panicle initiation suggesting a possible relationship between these two events. Rewatering of droughted plants that reached first wilting point caused an increase in both the number and length of the NR components but not the SR components.