The manual line-intercept (MLI) method is widely accepted as the stand
ard method of estimating root length. Recently, however, semiautomated
systems employing a digital line-intercept (DLI) method have been dev
eloped. Although the DLI method is said to represent a significant tim
e savings over the MLI method, comparisons between the two methods are
relatively scarce. This study was conducted to determine and compare
root length estimates obtained using manual and digital line-intercept
methods and to evaluate different methods of preparing root subsample
s for analysis. Roots were collected from spring wheat (Triticum aesti
vum L.) inoculated with three different plant growth-promoting rhizoba
cteria and a vesicular-arbuscular mycorrhizal fungus. Subsamples were
cut from bulk root systems before or after they had been dried, and ro
ot lengths were estimated using both the MLI and DLI methods. Although
the DLI and MLI methods yielded highly correlated results (r(2) = O.8
80**) when the subsamples were dried before being cut, the DLI method
consistently underestimated root lengths and could not distinguish be
tween inoculant effects. This was attributed to the inability of the i
maging system to resolve small pieces of shattered root. When subsampl
es were prepared from fresh root material, the number of small root fr
agments was minimized; the two methods yielded highly correlated resul
ts (r(2) = 0.943**) and both methods were equally adept at distinguis
hing significant differences between inoculant effects. Accurate root
length estimates can be obtained using the DLI method with subsamples
prepared from fresh roots in one- to two-thirds Less time than can be
achieved with the MLI method.