Text and photos Marjo Hokka
Late blight (LB) caused by the oomycete pathogen (Phytophthora infestans) is the main disease affecting potato production. It is managed primarily with synthetic fungicides with multiple applications. This reliance makes potatoes one of the crops with the highest fungicide load.
To reduce chemical dependence and promote sustainable pest management, alternative and holistic solutions are needed. Host Resistance is one critical component in integrated pest management (IPM) strategy for the sustainable control of LB but is often quickly overcome due to the genetic diversity in pathogen populations. The decision support systems (DSS), which include the most effective biological control agents with optimal timing of application and host resistance were tested across a wide range of locations and by industry partners to ensure practical applicability.
Eco-friendly solutions
ECOSOL (Eco-friendly solutions for the integrated management of late and early blight of potatoes) -project was run in five European countries in years 2021-2023. Its goal was to integrate biological control into IPM programs to manage late and early blight in potatoes. The newest article illustrates the efficacy of various biological control agents (BCAs) and plant resistance inducers (PRIs) to control LB disease development.
The study explores BCAs and PRIs as sustainable alternatives for chemical control, which could be introduced in DSS. BCAs and PRIs are suitable for organic production also. Totally 17 BCAs and 3 PRIs were screened in a detached leaf assay (DLA) and the most effective ones were selected for further trials. They were tested in planta and work was carried out to understand their mode of activity in order to secure stewardship into the future. The chosen BCAs—Polyversum (Pythium oligandrum), Nvs 2 (Bacillus amyloliquefaciens), TC 4 (Trichoderma atroviride), TC 6 (T. harzianum)—and the PRI ChiProPlant (Chitosan hydrochloride) were tested in glasshouse and field trials across five European countries. In glasshouse trials, ChiProPlant and T. atroviride significantly controlled late blight.
The importance of factors including timing of application and level of host resistance on their efficacy was investigated. The applied doses did not affect the efficacy of most BCAs and PRI; however, application timing proved to be crucial in the glasshouse trials. Treatments applied 1 and 5 days before inoculation were most effective, while post-inoculation treatments were least effective. Field trials showed that weekly applications of ChiProPlant, Polyversum, and Bacillus amyloliquefaciens significantly reduced LB infection. The study highlights the potential of BCAs and PRIs in LB management but underscores the need for further research to optimize their integration into IPM strategies.
None of these microbiological products are accepted in the plant protection product register in Finland. However basic substances such as Chitosan hydrochloride are allowed to use for plant protection in organic production according to EU regulations (EU2021/1165).
Importance of pathogen monitoring
ECOSOL-project was a part of EuroBlight -network, which has been established already 30 years ago. EuroBlight has published list of Best Practices, which also includes practices that can be implemented for organic potato production. Due to ECOSOL -project Finland was able to join the network again after 20 years and to take part of pathogen monitoring.
Approximately 2800 samples of LB were analysed in 2024 across Europe. This year the project aims to collect 1500 LB samples from main potato production areas in Europe. Samples are analysed using standardised 12 plex Euroblight SSR genotyping. The results will provide insight in the international, national and regional structures of the P. infestans EU population through e.g. the proportion (and dynamics) of the different currently known clonal lineages and unique “Other” genotypes in the population.
Latest results (year 2024) show that LB population in Finland represents “Other” genotypes and none of the novel and invasive genotypes were assessed in Finland. Results are promising as it seems that either host resistance has not been overcome or sensitivity to certain chemicals has not been lost in practice in Finland. It is important to monitor the evolution of pathogen as part of holistic and sustainable control of LB.
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The original article: Use of Biological Control Agents and Plant Resistance Inducers for the Control of Potato Late Blight (Phytophthora infestans)