Adaptation to Brassica Host Genotypes by a Single-Spore Isolate and Population of Plasmodiophora brassicae (Clubroot)

Abstract

LeBoldus, J. M., Manolii, V. P., Turkington, T. K., and Strelkov, S. E. 2012. Adaptation to Brassica host genotypes by a single-spore isolate and population oí Plasmodiophora brassicae (clubroot). Plant Dis. 96:833-838.Plasmodiophora brassicae, the cause of clubroot of crucifers, is an increasingly important pathogen of canola (Brassica napus) in Alberta, Canada. In response, clubroot-resistant canola genotypes are being deployed to help reduce yield losses. Two experiments were conducted to examine the effect on P. brassicae virulence of repeated exposure of a population and single-spore isolate of the pathogen to the same host. The first experiment examined changes in the index of disease over five cycles of infection on seven Brassica hosts (European Clubroot Differential [ECD] 02, ECD 04, ECD 05, ECD 15, '45H26', '45H29', and 08N823R). The second experiment tested the virulence of five cycled populations ('45H29', 08N823R, ECD 05, and ECD 15) and three cycled single-spore isolates ('45H29', 08N823R, and ECD05) on four resistant canola genotypes {'13-11', '73-67', VT-SD-09, and '9558C'). The results from these experiments clearly demonstrate the ability of both single-spore isolates and populations of P. brassicae to rapidly erode the resistance present in the two canola genotypes, '45H29' and 08N823R. Although the index of disease increased on these two genotypes, the four resistant canola genotypes remained resistant to all the cycled populations and single-spore isolates in the second experiment. These results underscore the importance of crop rotation in the management of clubroot in Alberta.

A comparison of clubroot development and management on canola and Brassica vegetables

“…Also, cortical infection and the subsequent development of resting spores have been reported in several non-cruciferous plant species, such as Indian cress and beet (Beta vulgaris L.) (Ludwig-Müller et al, 1999). The cropping of resistant cultivars may stimulate resting spore germination, thereby reducing the viable spore population in the soil, while no (or few) viable resting spores will be produced on the resistant plants to contribute to soil inoculum loads LeBoldus et al, 2012).…”

“…However, none of these cultivars are immune to clubroot . A proportion of the plants of each cultivar develop small galls under high inoculum pressure in the field (LeBoldus et al, 2012). These infected plants may be the result of segregation or incomplete gene penetrance, or may represent the first stage of pathogen adaptation to the resistance gene(s) in these cultivars.…”

Pathotypes of Plasmodiophora brassicae causing damage to oilseed rape in the Czech Republic and Poland

“…Pathotype 7 was predominant and in both Poland and the Czech Republic, representing around 43-44 % of the studied populations. The differences between the countries were even greater when the pathotype classification was based on the threshold of ID < 50 % with CI of 95 %, as described by LeBoldus et al (2012). In this case, there were eight pathotypes in Poland and six in the Czech Republic, with only five in common to both countries.…”

“…For ID 25 %, there were nine and 10 pathotypes in Poland and the Czech Republic, respectively, with only one (16/14/31) common to both countries. Based on an ID < 50 % with the 95 % CI not exceeding 50 % (LeBoldus et al 2012), 15 pathotypes in total were identified, with four in common: 16/2/14, 16/14/12, 16/14/15 and 16/31/8. The most common pathotype was 16/14/15 and it constituted over 23 % of the whole population.…”

“…Two thresholds were compared; ID 25 % as described by Somé et al (1996) and ID < 50 % with the 95 % confidence interval (CI) not exceeding 50 %, as proposed by LeBoldus et al (2012). Statistical analysis was carried out using Statistica v. 7.0 (StatSoft Inc., USA) and Microsoft Excel 2010 (Microsoft, Inc., USA).…”