Clubroot disease (CD), caused by Plasmodiophora brassicae, is one of the most economically important diseases affecting the Brassicaceae family of plants. We investigated the effect of CD on the yield of Hanana (Brassica rapa var. nippo-oleifera), a Brassica vegetable cultivated for young inflorescences and stalks as edible parts. Infested field plots with different severity levels of CD were prepared, and the disease was suppressed by pre-treatment with fungicide for nearly non-infested field plot as a control. As evaluation parameter, the fresh weights of edible parts and the plant top were measured. Assessment of plant growth and disease severity was done before harvest. Compared with the control, plant weight was significantly lower for plants grown in the plot with high disease severity. The yield of edible parts showed a tendency of decrease in the infested plots. A yield reduction of 65% was shown at the highest level of disease severity (99.4), whereas yield reductions were estimated at approximately 20% in plots with the moderate level (21.1–38.3). The present study quantified crop losses in a field of Hanana, and thus may be valuable for assuming the impact of CD specific to Hanana production.
