PhD student, University of Alberta
Epidemiologic study to asssess the P. brassicae distribution at vertically and horizontally
Clubroot disease is an important disease wich causes serious losses all around the world in different cruciferous crops. Its management is quite difficult, since it can cause losses between 20 and 100% in crops and it produces resting spores which can keep viable in soil for even 20 years. Taking into account the issue that this disease represents, it is necesary to understant it deeply in order to figure out the most appropiate management tools in each case. Epidemiology, focus in the pathogen distribution, spread and the factors which affect its stablishment and development are addresed in this pinboard. In this topic my team has donde two main researches, focun in evaluate the dpathogen distribution in field and the presence of viable inoculum in the irrigation water. In the fisrt one we aimed at describing spatial patterns of inoculum density (ID) for resting spores of Plasmodiophora brassicae. the pathogen of clubroot of crucifers, in a 3D approach and relate them to disease development. Soil sampling was done in a commercial field of broccoli in a grid of 30 x 20 m, with 30 georeferenced points; at each point, samples were collected at 15 cm and 30 cm depth. ID quantification was done according to Takahashi and Yamaguchi (1987). Finally, a bio-assay in greenhouse conditions was done on hybrid ‘Delus’ cabbage plants; incidence and severity were measured 80 days after planting. Average ID per gram of soil at 15 cm was 1∙106 resting spores while at 30 cm it was 7∙105 resting spores. Incidence and severity did not show differences among depths. The spatial structure analysis using variograms, showed an anisotropic trend at 45°. Structural variance was between 95% and 100% that confirmed that ID and severity variance are almost completely explained by the spatial variation. All estimated semivariograms were adjusted to the spherical model. Range value, which estimates the patch size, at 15 cm was 77.14 m for ID and severity, while at 30 cm it was 34.96 m for ID and 24.58 m for severity. In summary, P. brassicae shows a patchy distribution in the horizontal axis, while in the vertical axis, the deeper the lesser inoculum density and the smaller the patch size.
Abstract: Single spore derived isolates of Plasmodiophora brassicae are difficult to be generated due to its biotrophic life style. Two methods to produce pure pathotype isolates of P. brassicae were compared. A new technique for the inoculation of Brassica seedlings with single root hairs infected by P. brassicae is described, which is taking advantage of the multiplication of P. brassicae during the first infection cycle in root hairs. Ten single spore derived isolates from 328 single sporangiosorus inoculations were produced using different populations of P. brassicae. To compare success rates inoculations with single resting spores were also made. From 125 inoculations with single resting spores only one single spore derived isolate was achieved. The root hair inoculation method was more practicable than most hitherto reported methods and offers a reasonable efficacy for the production of single spore derived isolates.
Pub.: 18 Feb '16, Pinned: 01 Jul '17
Abstract: Between 2012 and 2015, 49 new clubroot‐infested fields were identified in 12 German federal states. Clubroot disease incidence varied within these fields from 22% to 92%. Field information revealed that in 85% of fields, oilseed rape was grown in rotation once every 2 or 3 years. Frequency of OSR in the rotation was significantly correlated with the incidence and prevalence of clubroot disease. The disease was detected in fields with soil pH ranging from 5.1 to 8.3, and a significant negative correlation was found between soil pH and the disease incidence of infested fields. Furthermore, more cases of disease and severe incidences were observed in sandy loam and loamy sand as compared with other soil types. Pathotype classification of the 49 Plasmodiophora brassicae populations was conducted on two differential sets, the European Clubroot Differential set and the set of Somé (1996). Additionally, the degree of virulence of the collected isolates was analysed on the clubroot‐resistant oilseed rape cv. Mendel. The results showed variation in pathotype distribution in different regions in Germany. The majority of isolates according to Somé were pathotypes 1 and 3, respectively, with pathotypes 2 and 5 in the minority. Detailed classification according to Buczacki showed the dominance of 16/31/31, 16/14/30 and 16/14/31 populations among 20 distinct virulence patterns of collected isolates. From all populations tested for virulence on cv. Mendel, 15 isolates were found to be moderately or highly virulent. These virulent populations were not restricted to a small geographical area in the country.
Pub.: 11 Jul '16, Pinned: 01 Jul '17
Abstract: Clubroot disease caused by Plasmodiophora brassicae is one of the most serious diseases in Brassica crops worldwide. In this study, the pathotypes of 12 Korean P. brassicae field isolates were determined using various Chinese cabbage including 22 commercial cultivars from Korea, China, and Japan, and 15 inbred lines. All P. brassicae isolates exhibited the typical clubroot disease on non-clubroot resistant cultivar, indicating that the isolates were highly pathogenic. According to the reactions on the Williams' hosts, the 12 field isolates were initially classified into five races. However, when these isolates were inoculated onto clubroot-resistant (CR) cultivars of Chinese cabbage, several isolates led to different disease responses even though the isolates have been assigned to the same race by the Williams' host responses. Based on the pathogenicity results, the 12 field isolates were reclassified into four different groups: pathotype 1 (GN1, GN2, GS, JS, and HS), 2 (DJ and KS), 3 (HN1, PC, and YC), and 4 (HN2 and SS). In addition, the CR cultivars from Korea, China, and Japan exhibited distinguishable disease responses to the P. brassicae isolates, suggesting that the 22 cultivars used in this study, including the non-CR cultivars, are classified into four different host groups based on their disease resistance. Combining these findings, the four differential hosts of Chinese cabbage and four pathotype groups of P. brassicae might provide an efficient screening system for resistant cultivars and a new foundation of breeding strategies for CR Chinese cabbage.
Pub.: 11 Oct '16, Pinned: 01 Jul '17
Abstract: To mitigate the impact and dissemination of clubroot in western Canada, canola (Brassica napus) producers have relied on clubroot resistance traits. However, in 2013 and 2014, new strains of the clubroot pathogen, Plasmodiophora brassicae, emerged that are virulent on most clubroot-resistant (CR) canola genotypes. Novel strains of the pathogen were inoculated onto two susceptible canola cultivars, one resistant line and six CR cultivars. Although all cultivars/lines showed a susceptible response to inoculation with the new strains of P. brassicae, the severity of disease reaction, root hair infection rates and the amount of P. brassicae DNA present in each canola genotype varied depending on the strain. In addition, the effect of inoculum density on disease severity and gall formation was recorded for one of these new strains on a universally susceptible Chinese cabbage cultivar and one susceptible and 10 resistant canola genotypes. Although root galls were observed at an inoculum density of 103 spores per mL of soil, clear differentiation of susceptible and resistant reactions among canola cultivars/lines was not observed until the inoculum density reached 105 spores mL−1. At a spore density of 106 spores mL−1 and above, all cultivars/lines developed susceptible reactions, although there was some differentiation in the degree of reaction. This study shows the potential to develop a unique disease profile for emergent clubroot pathotypes and shows a useful range of spore densities at which to study new P. brassicae strains.
Pub.: 21 Mar '17, Pinned: 01 Jul '17