Combining Different Potato-Associated Pseudomonas Strains for Improved Biocontrol of Phytophthora infestans

Abstract

Late blight caused by Phytophthora infestans is considered as the most devastating disease of potato and is a re-emerging problem worldwide. Current late blight control practices rely mostly on synthetic fungicides or copper-based products, but growing awareness of the negative impact of these compounds on the environment has led to the search for alternative control measures. A collection of Pseudomonas strains isolated from both the rhizosphere and the phyllosphere of potato was recently characterized for in vitro protective effects against P. infestans. In the present study, we used a leaf disk assay with three different potato cultivars to compare the disease inhibition capacity of nine selected Pseudomonas strains when applied alone or in all possible dual and triple combinations. Results showed a strong cultivar effect and identified strains previously thought to be inactive based on in vitro assays as the best biocontrol candidates. One strain was much more active alone than in combination with other strains, while two other strains provided significantly better protection in dual combination than when applied alone. A subset of five strains was then further selected to determine their mutual influence on each other’s survival and growth, as well as to characterize their activity against P. infestans in more details. This revealed that the two strains whose dual combination was particularly efficient were only weakly interfering with each other’s growth and had complementary modes of action. Our results highlight the potential to harness the crop’s native rhizosphere and phyllosphere microbiome through re-assembling strains with differing modes of action into small communities, thereby providing more consistent protection than with the application of single strains. We consider this as a first step toward more elaborate microbiome management efforts, which shall be integrated into global strategies for sustainable control of potato late blight.

Linking Comparative Genomics of Nine Potato-Associated Pseudomonas Isolates With Their Differing Biocontrol Potential Against Late Blight

“…For the colonization assays, only the assay on Lady Claire was retained and a colonization performance score was attributed to each strain, by calculating the percentage of the number of times the bacteria were successfully retrieved from the stem cuts over the total number of stem cuts made for the three different heights. Data on the inhibition of P. infestans development on potato leaf discs of cultivars Bintje, Lady Claire and Victoria was retrieved from a previous study (De Vrieze et al, 2018) and added to the phenotypic table. In these experiments, mixtures of sporangia and bacterial suspensions were pipetted on potato leaf discs.…”

“…In addition to classical biocontrol approaches relying on one particular organism, we have recently investigated the protection potential of dual and triple combinations of Pseudomonas strains on three potato cultivars (De Vrieze et al, 2018). When we assessed the survival rates of R32, R47, S19, S35, and S49 when co-incubated in double and triple combinations, we noticed that S49 appeared to be a good partner to all strains, except to R47, by which it was largely outcompeted.…”

“…Some of these Pseudomonas strains caused a strong reduction of pathogen growth in vitro both through emission of volatile compounds (De Vrieze et al, 2015;Hunziker et al, 2015) and through diffusion of non-volatile metabolites (Guyer et al, 2015;Hunziker et al, 2015). Moreover, significant reduction of disease symptoms was observed on leaf discs treated with single (Guyer et al, 2015) or combinations of (De Vrieze et al, 2018) the Pseudomonas strains. This anti-Phytophthora activity was consistently observed against a collection of genetically diverse lineages of P. infestans (De Vrieze et al, 2019).…”

Tissue-specific synergistic bio-priming of pepper by two Streptomyces species against Phytophthora capsici

“…Co-inoculation of biocontrol agents displayed a more pronounced impact on the microbial structure of rhizosphere than a single application [11]. Some studies have evaluated the effects of Actinomycetes consortium from either the same or different taxonomic groups [12,13,14,15]. The research programs have mostly focused on biocontrol of damping-off caused by Phytophthora species in the seedling stage (root and crown rot), with minimal consideration about fruit blight disease on pepper caused by P. capsici [16,17].…”

Transcript accumulation in a trifold interaction gives insight into mechanisms of biocontrol

“…An alternative possibility to control diseases caused by soil‐borne pathogens has emerged from the study of ‘suppressive soils’ in which biotic agents suppress disease despite the presence of a pathogen (Schlatter et al ., ). This phenomenon was termed biocontrol, and has now been demonstrated in a wide variety of crops (De Vrieze et al ., ; Newitt et al ., ). However, the mechanisms underlying biocontrol remain largely elusive.…”