Plant root systems are pivotal for ecological success, ecosystem functioning, and nutrient and water acquisition. In the first phase of this project, root system architecture (RSA) traits of 379 Brassica accessions, representing the six most economically important Brassica species (B. napus, B. juncea, B. carinata, B. oleracea, B. nigra, and B. rapa), were phenotyped using a semi-hydroponic system and image analysis software. Of these, 177 accessions had large root systems, 29 had medium-sized roots, and 173 had small-sized root systems. Brassica napus and B. oleracea exhibited the largest and most complex root systems, while B. nigra had the smallest roots; B. juncea and B. carinata showed comparable complexity with larger root diameters. Accessions of all species displayed variable RSA traits, showing promise for the breeding of Brassica crops suited to different environments. In the second phase of this project, the effects of fertilizer rates on clubroot severity and yield parameters were examined. Ninety-six Brassica accessions were grown in soilless mix inoculated with pathotypes 3A and 3H of the clubroot pathogen, Plasmodiophora brassicae. Clubroot symptoms developed 5 to 10 days earlier in plants fertilized (NPK 20:20:20) at recommended (RF; 0.95 g/L) and higher rates (HF; 3.8 g/L) compared to unfertilized plants (NF). However, after 8 weeks, no significant differences in clubroot severity were observed among the treatments. Conversely, fresh and dry gall weights significantly increased (130%-550%) in the RF and HF treatments compared to the NF treatment. Plant height, number of branches, and silique count were also significantly higher (by 30% to 50%, 130% to 1200%, and 140% to 430%, respectively) in the RF and HF treatments, indicating improved yield parameters with fertilizer application despite clubroot presence. Thus, while fertilizer application significantly enhanced yield parameters, it also accelerated the onset of clubroot and promoted larger galls.