Control of clubroot disease on Hanana (flower nabana) using dry seaweed powders

Abstract

Clubroot disease caused by Plasmodiophora brassicae Woronin is one of the most economically important diseases affecting the Brassicaceae family of plants. We evaluated the potential effectiveness of seaweeds on reducing the severity of clubroot disease in Hanana (Brassica rapa L. var. nippo-oleifera Kitam.), a semi-traditional vegetable in Kyoto, Japan. The efficacy of dry powders of brown and red algae (Sargassum horneri C. Agardh and Gracilaria sp.) collected in northern Kyoto Prefecture, and a commercial granular formulation made from brown alga Ascophyllum nodosum Le Jolis was compared with the fungicide amisulbrom under field conditions. No impact was observed when seaweeds were added to infested field soil before transplanting at a dose of 100 kg/10 a. Conversely, cultivation of plug seedlings in a mix of seaweeds and non-infested culture soil for 3 weeks before transplanting into an infested field was effective. Although the protective values of seaweed treatments were less than those of fungicides, all seaweed treatments tended to reduce disease severity, particularly under relatively mild disease pressure in a field. A significant inhibition of growth was observed with 1.5% seaweed powder treatment when plug seedlings were grown under subirrigation with a tray, but this did not occur when under overhead irrigation with a misting device.