Compensatory Growth in the Crown Root System of Sorghum1

Abstract The number of crown roots which develop on grain sorghum (Sorghum bicolor (L.) Moench) plants under field conditions is often reduced far below the genetic potential. As a first step toward understanding the significance of the number of crown roots to total function of the root system, we conducted experiments to determine the capacity for growth when root numbers were restricted by clipping treatments and water and nutrients were not limiting. When grown in hydroponics, ‘RS610’ sorghum plants developed an average of 20.6 crown roots by 50 days after planting (DAP). Root clipping treatments, initiated when plants were young, gave groups of plants in which 3, 6, and 10 crown roots were allowed to develop. For plants with at least six roots, leaf areas, shoot, and root dry weights were not different from controls. Plants maintained with only three roots had reduced leaf areas and lower shoot and root dry weights by 50 DAP; however, branching and growth of second and third order lateral roots were promoted. When compared at equal leaf areas, total root lengths and root volumes were equivalent for all treatments. Thus, compensatory growth within the existing root members was capable of maintaining root length and volume, but not root dry weight when crown root numbers were severely reduced.