Until recently, genotypes of Phytophthora infestans were regionally distributed in Europe, with populations in western Europe being dominated by clonal lineages and those in northern Europe being genetically diverse because of frequent sexual reproduction. However, since 2013 a new clonal lineage (EU_41_A2) has successfully established itself and expanded in the sexually recombining P. infestans populations of northern Europe. The objective of this study was to study phenotypic traits of the new clonal lineage of P. infestans, which may explain its successful establishment and expansion within sexually recombining populations. Fungicide sensitivity, aggressiveness, and virulence profiles of isolates of EU_41_A2 were analyzed and compared with those of the local sexual populations from Denmark, Norway, and Estonia. None of the phenotypic data obtained from the isolates collected from Denmark, Estonia, and Norway independently explained the invasive success of EU_41_A2 within sexual Nordic populations. Therefore, we hypothesize that the expansion of this new genotype could result from a combination of fitness traits and more favorable environmental conditions that have emerged in response to climate change.

Late blight ( Phytophthora infestans ) is a major disease in potato cultivation, managed primarily with synthetic fungicides. This reliance makes potatoes one of the crops with the highest fungicide load. To reduce chemical dependence and promote integrated pest management (IPM), alternative solutions are needed. This study explores biological control agents (BCAs) and plant resistance inducers (PRIs) as sustainable alternatives. We screened 17 BCAs and 3 PRIs in a detached leaf assay (DLA) and selected the most effective for further trials. 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 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 late blight infection. However, none matched the efficacy of synthetic fungicides. This study highlights the potential of BCAs and PRIs in late blight management but underscores the need for further research to optimize their integration into IPM strategies.

This study explores the population dynamics of Phytophthora infestans in Estonia from 2005 to 2022, focusing on genetic diversity and potential shifts in reproductive strategies. In total, 153 P. infestans isolates were collected throughout Estonia over ten growing seasons. Genotyping revealed considerable genetic diversity, with most isolates not corresponding to known multilocus genotypes (MLGs). Still, instances of invasive clonal lineages were observed, notably EU_41_A2. The data indicate the likelihood of random mating rather than clonal reproduction in all the analyzed years. The principal coordinate analysis (PCoA) results revealed no distinct clustering among the sampling years. Statistical analysis and the minimum spanning network (MSN) indicated low genetic differentiation between years with minimal fluctuations in allele frequencies. The continuous monitoring of P. infestans populations is essential for detecting any changes from the current evolutionary trajectory and implement effective disease management strategies, especially considering the recent emergence of EU_41_A2 in the Nordics and the potential impacts of climate change.