MANUAL AND DIGITAL LINE-INTERCEPT METHODS OF MEASURING ROOT LENGTH - A COMPARISON

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.