EFFECTS OF COMMON ROOT-ROT ON DISCOLORATION AND GROWTH OF THE SPRING WHEAT ROOT-SYSTEM

Image analysis procedures were used to quantify the effect of common r oot rot on the growth and discoloration of the subcrown internode (SCI ), crown roots, and seminal roots of spring wheat. Severe discoloratio n of the SCI was associated with diminished growth of the seminal and crown roots. The linkage of discoloration of the SCI to a reduction in root growth was most evident for the crown roots. Reduced growth of e ither the crown or seminal roots was not compensated for by increased growth of the other root system. The differences in root discoloration among different root rot categories were generally small. On average, the crown and seminal roots were whiter than the SCI in the healthy ( nil) category; There was a weak negative relationship between discolor ation of the SCI and the crown and seminal root systems. However, it w as also observed that root discoloration usually increased with greate r root length. Since plants with healthy SCIs usually had longer roots , they were more likely to be exposed to the pathogen and become disco lored than were plants with severely diseased SCIs. The image analysis procedures developed in this study can be used to objectively and pre cisely measure damage caused by root diseases in other host species. T his procedure validates the most commonly used field research method o f rating plants for common root rot.