The Evaluation of Lime Products as a Clubroot (Plasmodiophora brassicae) Management Tool

• Author / Creator

  Fox, Nicole M

• Clubroot, caused by Plasmodiophora brassicae Wor., is a soil-borne disease that has become a constraint to canola (Brassica napus L.) production in Alberta, Canada. The disease is managed primarily by the planting of clubroot resistant cultivars, but resistance has been overcome in close to 200 fields in the province. Clubroot development is favoured in acidic soils; therefore, increasing soil pH may reduce disease severity in infested soils and serve as another management tool. The efficacy of hydrated lime products in reducing clubroot severity was assessed in replicated field plot experiments in central Alberta in 2017 and 2018. In 2017, the application of moderate to high rates of hydrated lime significantly reduced clubroot severity and increased above-ground biomass in a susceptible canola cultivar 8 weeks after planting. At the highest application rate of 11.4 T ha-1 and 12.7 T ha-1, lime treatment reduced the clubroot disease severity index by 35-91%, while increasing above-ground plant biomass by 58-116%. In contrast, no effect of lime treatment was observed in the 2018 field trials, possibly due to a longer interval between lime application and sowing, as well as reduced rainfall received during this time. A greenhouse study also was conducted to compare the efficacy of hydrated lime and limestone in reducing clubroot severity in susceptible and moderately resistant canola cultivars, at different application rates and inoculum concentrations. In the control treatments, indices of disease severity were very high (92-100%) in the susceptible canola and low (9-13%) in the moderately resistant canola. The application of hydrated lime at 4.7, 8.1, 11.4, and 14.8 T ha-1 completely eliminated visible clubroot symptoms in both cultivars, whereas limestone decreased disease severity only at the two lowest inoculum concentrations. Other parameters including plant height and root and shoot weight fluctuated closely with the level of disease control. Root tissues from the greenhouse study were analyzed by quantitative-PCR (q-PCR) to measure P.
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  brassicae proliferation in planta. Inoculum concentration and the type and rate of lime product applied significantly affected the amount of P. brassicae DNA in the root tissue. Pathogen DNA could not be detected in 10-day-old seedlings following the application of hydrated lime, but the rate required to prevent root colonization increased with increasing inoculum concentration. Limestone application also appeared to provide some control, but P. brassicae DNA still was detectable in the host roots. Repeated trials with less virulent inoculum revealed similar trends, suggesting that limestone could be applied in soils with lower inoculum concentrations to reduce clubroot severity and root infection. Based on the greenhouse and q-PCR results, hydrated lime appears to be more effective than limestone for clubroot control, but the latter was not evaluated under field conditions. Nonetheless, hydrated lime may represent an effective tool to manage P. brassicae in highly infested patches in a field, at field entrances and in acidic soils, by reducing clubroot severity on susceptible and resistant hosts. As such, the application of lime may help to supplement the use of genetic resistance, by reducing disease pressure and the potential for pathotype shifts.

• Subjects / Keywords

  • lime
  • Plasmodiophora brassicae
  • clubroot
  • canola

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-1pgy-hf49

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.