First Report of Plasmodiophora brassicae on Cabbage in Eastern North Carolina

Abstract

Clubroot, caused by Plasmodiophora brassicae Woronin, has occurred for at least 50 years in three counties in northwestern North Carolina, but has not been reported previously from eastern North Carolina, where most commercial cabbage is produced. In the fall of 1995, clubroot was observed in a direct seeded, commercial cabbage field in Plymouth, NC. Diseased cabbage plants were stunted and roots exhibited clublike swellings. Clubs were randomly harvested from roots of five plants to obtain a composite isolate to determine which race(s) of P. brassicae are infecting cabbage in eastern North Carolina. Three experiments were conducted, using the procedure of Williams (2). Four replicates of 10, 1-week-old seedlings of eight different crucifer cultivars were inoculated by dipping in a spore suspension (1 × 108 cysts/ml) of P. brassicae and planted in pasteurized potting mix. Seedlings dipped in sterile water served as controls. Inoculated seedlings were incubated in a greenhouse at 18 to 28°C for 6 to 8 weeks and assessed for clubroot incidence and severity. The isolate of P. brassicae from eastern North Carolina was most virulent on cabbage (Brassica oleracea var. capitata cv. Jersey Queen), collard (B. oleracea var. acephala cv. Vates), and wild mustard (B. nigra); moderately virulent on canola (B. napus cv. Brutor) and rutabaga (B. napus cvs. Laurentian and Wilhelmsburger); and least virulent on cabbage (cv. Badger Shipper). Canola (B. napus cv. Nevin) and control seedlings were not infected and exhibited no symptoms. Similar results were obtained for all experiments. Based on these results, the isolate of P. brassicae from eastern North Carolina was designated as race 6 and pathotype 5 according to Williams (2) and Some (1), respectively. However, further experiments with single-cyst-derived isolates from individual clubs obtained from different geographic locations are needed to accurately characterize field populations of P. brassicae on cabbage in eastern North Carolina. References: (1) A. Some et al. Plant Pathol. 45:432, 1996. (2) P. H. Williams. Phytopathology 56:624, 1966.

Occurrence of Clubroot on Pak-Choi Caused byPlasmodiophora brassicae

“…The clubroot pathogen was identified as Plasmodiophora brassicae Woronin based on its morphological and pathological characteristics, which were consistent with those described by Buczacki (1979). It was reported that P. brassicae causes clubroot of crucifers (Buczacki, 1979; Cubeta et al, 1998; Linnasalmi and Toiviainen, 1991). The disease has been a major problem in areas where Chinese cabbage and some other cruciferous crops are cultivated in Korea (Cho et al, 2003; Kim and Oh, 1997).…”