The Evaluation of Lime Products as a Clubroot (Plasmodiophora brassicae) Management Tool
Bibliographic record
Abstract
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. iii 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.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".