Quantification of common root rot symptoms in resistant and susceptible barley by image analysis

A series of tests were carried out to determine the effect of common root rot, caused by Cochliobolus sativus, on root growth and discolouration in the moderately resistant cv. Bonanza and the susceptible cv. Gateway of barley. An image analyser was used to quantify the growth and discolouration (mean intensity) of the roots and the subcrown internode (SCI) of individual plants. The plants were also visually rated for root rot severity and their root dry weight was determined. In the absence of disease, no differences in root discolouration or growth were observed between the two barley cultivars. In plants grown in naturally infested soil, visual root rot ratings and mean intensity values indicated that the SCls of Bonanza were less discoloured than those of cv. Gateway. In cv. Gateway, higher levels of disease were usually associated with a smaller root system than in cv. Bonanza, but the effect was significant (P 0.05) ...