Soybean root systems and sudden death syndrome severity: Taproot and lateral root infection

Experiments were conducted in the greenhouse to evaluate the role that infection location (taproot versus lateral root) plays in disease development of sudden death syndrome (SDS) on soybean (Glycine max) caused by the fungus Fusarium solani f. sp. glycines. Root characteristics of 12 soybean cultivars, representing a range of SDS reactions, were evaluated and compared for disease responses. A method was developed to facilitate taproot or lateral root infection. Results show that this procedure may be useful for observing a continuum of foliar and root disease responses. Significant differences in root length, surface area, and average diameter were observed among cultivars when infection occurred at the taproot or on the lateral roots. A significant correlation existed between foliar symptoms (i.e., area under the disease progress curve [AUDPC]) and root length, surface area, and volume for inoculated plants. Root volume and percent root discoloration were significantly different among individual soybean cultivars, and percent root discoloration was associated with AUDPC values only when the initial site of infection was on the lateral roots of soybean plants. Useful information about root system responses to SDS may be obtained from infection of the entire root system as opposed to only taproot infection.