Digital images for determining root traits have been analyzed using WinRHIZO commercial software. A freeware ImageJ has been developed for the analysis but whether root lengths assigned to root diameter classes obtained by this method correspond to those estimated by WinRHIZO has not been confirmed. In this study root lengths estimated using ImageJ were compared with those estimated using WinRHIZO. In ImageJ the root lengths were estimated using a triangle thresholding algorithm that was valid for total root length in our previous study. For the small-diameter classes (<0.5 mm) the estimates obtained using ImageJ and the conversion factor 2/3 corresponded closely to the estimates obtained using WinRHIZO. For large-diameter classes (>0.5 mm) root lengths estimated using ImageJ were similar to those obtained using WinRHIZO without using the conversion factor. These results were valid for rice roots. In this report we propose completely automated estimation of root lengths for roots in each diameter class by using ImageJ.
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