A review on clubroot of crucifers: symptoms, life-cycle of pathogen, factors affecting severity, and management strategies

Abstract

Clubroot is a devastating disease of crucifers throughout the world. It is caused by a soil-borne obligate phytoparasite, Plasmodiophora brassicae Wor. Plant affected by this disease shows flagging of leaves, unthrifty growth, and even premature death. When uprooted, root shows characteristic symptom of hypertrophied club-shaped root system. Several biotic and abiotic factors affect the disease severity. Biotic factors include spore load in soil and virulence of pathogen, whereas abiotic factors generally include soil environmental factors such as soil temperature, soil pH, soil moisture, and soil type. Pathogen survives, for substantial period of time in absence of host, through its double-walled resting spores in soil or crop debris. Temperature affects spore germination, occurrence, and pathogen proliferation. Acidic soil reaction is crucial for pathogen to proliferate, metabolize, secret enzymes, and to complete lifecycle. All type of soil textures favor disease; however, severity differs with type of soil and soil organic matter content. Soil moisture provides platform to move bi-flagellated zoospores to infect root hairs of crops. Root hair infection is commensurate with inoculum density or spore load in soil. Immediate management strategies entail cultural practices, use of biocontrol agents, and application of chemical as last resort. Trichoderma spp., Pseudomonas fluorescens, Bacillus subtilis, and Gliocladium catenulatum are potential biocontrol agents. Flusalfamide, Fluazinam, and Cyazofamid are some common chemicals used to control clubroot. Soil carried by farm implements, human body, irrigation water, and flood can be potential source of pathogen. The risk of clubroot can be reduced by ensuring phyto-sanitory measures, destroying host crop debris, regular scouting, growing resistant cultivars, avoiding acidic soil reaction, eliminating weedy hosts, and reducing soil movement.

Early-stage responses toPlasmodiophora brassicaeat the transcriptome and metabolome levels in clubroot resistant and susceptible oilseedBrassica napus

“…7,9 As the pathogen-induced clubroot galls form, the host root architecture is deformed, and the vascular system is severely damaged resulting in the poor conduction of water and minerals, leading to wilting and crop loss. [10][11][12] Several clubroot management strategies have been developed, including liming, crop rotation, application of biofungicides, and sanitization of farm tools; however, these approaches are not adequate. 13,14 The development of clubroot resistant (CR) cultivars has afforded canola producers some relief but the evolution of new pathotypes capable of overcoming resistance in the host plants continue to pose a challenge necessitating the development of novel genetic resources to mitigate crop loss due to this disease.…”

A brief note on the incidence and management of Plasmodiophora rassica

“…Alkaline soils were thought to mitigate the production of symptoms, and it was suggested that the pH of soils be increased between 7.3-7.5 for reasonable clubroot control. The question is whether the soil's alkalinity is responsible or part of the rise in calcium ions for a decreased infection (Gahatraj et al, 2019). Thalli that produced zoospores were deformed, and the development of clubs was terminated at a ground pH greater than 8.0.…”

Sustainability on the farm: breeding for resistance and management of major canola diseases in Canada contributing towards an IPM approach

“…Some commonly used chemicals against P. brassicae have been registered, such as Nebijin, pentachloronitrobenzene, Nano Silver Hydrogen peroxide, etc. (Gahatraj et al 2019).…”