Effect of host and non‐host crops on Plasmodiophora brassicae resting spore concentrations and clubroot of canola

Abstract

Plasmodiophora brassicae, causal agent of clubroot of crucifers, poses a serious threat to Canadian canola production. The effects of fallow (F) periods and bait crops (clubroot-susceptible canola (B) and perennial ryegrass (R)) on clubroot severity and P. brassicae resting spore populations were evaluated in five sequences: R-B, B-R, R-F, B-F and F-F. Both host and non-host bait crops reduced clubroot severity in a subsequent crop of a susceptible canola cultivar compared with fallow. Resting spore and P. brassicae DNA concentrations decreased in all treatments, but were lowest for the R-B and B-R bait crop sequences. In addition, two studies were conducted in mini-plots under field conditions to assess the effect of rotation of susceptible or resistant canola cultivars on clubroot severity and P. brassicae resting spore populations. One study included three crops of susceptible canola compared with a 2-year break of oat-pea, barley-pea, wheat-wheat or fallow-fallow. The other study assessed three crops of resistant canola, two crops of resistant canola with a 1-year break, one crop of resistant canola and a 2-year break, and a 3-year break with barley followed by a susceptible canola. The rotations that included non-host crops of barley, pea or oat reduced clubroot severity and resting spore concentrations, and increased yield, compared with continuous cropping of either resistant or susceptible canola. Growing of a susceptible canola cultivar contributed 23-250-fold greater gall mass compared with resistant cultivars.

Comparing the Infection Biology of Plasmodiophora brassicae in Clubroot Susceptible and Resistant Hosts and Non-hosts

“…Several studies have reported that non-host crops could be used as baits to reduce the soil-infested resting spores (Friberg et al, 2006;Ahmed et al, 2011;Hwang et al, 2015). However, the underlying mechanisms are still not clear.…”

“…Our results theoretically supported that the rotation of Brassica crops with non-host crops contributes to an integrative management to reduce the clubroot disease. In practice, the rotations with non-host crops barley, pea or oat not only reduced clubroot severity and resting spore concentrations, but also increased yield in contrast to continuous cropping of either resistant or susceptible canola (Hwang et al, 2015).…”

“…The hosts of clubroot disease always limit in the members of family Brassicaceae ( Dixon, 2004 ), despite occasional cases of which P. brassicae was reported to successfully infect some non-cruciferous species ( Ludwig-Müller et al, 1999 ). To efficiently and durably control the clubroot disease, attempts of using clubroot non-hosts as baits to reduce the soil-infested resting spores have been made in several cases ( Friberg et al, 2006 ; Ahmed et al, 2011 ; Hwang et al, 2015 ). However, potential infection, growth, and reproduction of P. brassicae within root tissues of non-hosts have not been understood, largely due to the lack of sufficient techniques to visualize or detect P. brassicae infection structures within plant tissues.…”

Comparison of techniques for estimation of resting spores of Plasmodiophora brassicae in soil

“…Several previous studies have estimated the half-life of resting spores of P. brassicae over time based on bioassays (Wallenhammar, 1996;Hwang et al, 2015). However, such bioassays are not suitable for a pathogen with a type III survival pattern because its survival is not constant over time or uniform among individuals in a population.…”

Reaction of clubroot-resistant genotypes of Brassica rapa, Brassica napus and Brassica oleracea to Polish Plasmodiophora brassicae pathotypes in laboratory tests

“…Depending on soil conditions, infestation rate, pathogenicity of P. brassicae local strains and susceptibility of a crop's variety, yield losses can range from 30% to even 100% (Wallenhammar 1996). In control of the disease, the most important are preventive treatments including usage of pathogen-free fields, early pathogen detection, non-host crop rotation, use of the bait, decoy or catch crops, maintaining the appropriate soil pH and soil drenches with fungicides (Murakami et al 2000;Peng et al 2014;Hwang et al 2015). However, these methods would not reduce clubroot severity in heavily infested fields and they are not cost effective.…”