|dc.description.abstract||The aim of this project was to develop treatments that would be able to reduce the
survival of clubroot spores in field soil and protect the roots of young transplants against
infection. The project focused on using combinations of treatments which integrate novel
and existing controls with emphasis placed on the sustainable use of waste materials,
plant materials and bioactives. A wide range of treatments were screened individually
and in combination under glasshouse and field conditions, e.g. fungicides, nutritional
amendments, companion planting, plant saponins and biocontrol agents.
Many of these treatments were able to reduce clubroot severity to varying degrees.
Glasshouse treatments were more successful at controlling disease than those applied in
the field. The most effective treatments - when applied correctly - contained calcium,
e.g. lime as calcium oxide or LimeX (a by-product of the sugarbeet processing industry),
and crushed scallop and whelk shells (a by-product of the fishing industry). Whilst the
effects of calcium and pH on clubroot are not new, growers need to think more in terms
of dose of calcium applied in the field rather than just pH, and also, the time of addition
of lime to soil before planting needs serious consideration as it may be optimal to apply
lime less than two weeks before transplanting.
Experimental results have shown that soil microflora plays a major role in the
development of clubroot disease and that the membrane potential of growing roots may
be one of the most important factors in preventing P. brassicae from entering plant roots
and causing disease due to the effect that calcium and pH have on clubroot control. The
experiments have also shown that there are interactions between treatments such as
fungicides, limes, soil nutritional level and soil microflora at controlling disease and
some treatments may reduce the effectiveness of other treatments at controlling disease.
Another factor that is known to affect the effectiveness of treatments at controlling
clubroot is the initial spore load in the soil. Therefore, an additional aim of the project
was to develop a rapid, quantitative PCR based diagnostic test that could measure the level of clubroot spores directly from soil. Plasmodiophora brassicae DNA was
successfully extracted and amplified from artificially inoculated soils and from naturally
infested field soils using real-time PCR with selected sets of primers and probes. Many
different types of soil DNA extraction methods were tested and standard curves relating
to different levels of spore inoculum were created.
This project has generated useful information as to why there are contradictory results in
clubroot research about the effect of various treatments at controlling clubroot. This
information may also be the basis of practical advice to brassica growers on best practices
to use to achieve optimal clubroot control in the field. Options in relation to new
sustainable control treatments are discussed in the light of the results from both
glasshouse and field experiments. These involve planting brassicas on raised beds and
applying treatments strategically around the root zone. LimeX 70 or powdered calcium
oxide were demonstrated to be the most optimal lime treatments for control, and a split
application of Perlka (granular calcium cyanamide) may prove to be a consistently
effective method for controlling clubroot.||en