Digital video technology as an aid for quantifying root rot

Evaluation of disease severity in root systems is usually subjective, based on observation and categorization into an arbitrary scale of several categ ories. Results obtained using this approach can vary according to the obser ver's experience. A new, simple method for evaluating and quantifying the r oot severity index (RSI) was developed. This method consists of surrounding the root pan with a transparent film and tracing all roots with a marker. On a secund transparency, only healthy roots are traced. Lengths of both he althy and diseased roots are measured with a root length/area meter (Dias I I). The method of peripheral root-hall root tracings was evaluated with poi nsettias infected with Pythium ultimum (Trow.). Results indicated that it w as as effective as the traditional method of determining RSI for total and peripheral roots.