Soft Rot Pectobacteriaceae (SRP) bacteria as Pectobacterium and Dickeya are phytopathogenic agents responsible of blackleg disease on several crop as potato, affecting the yield and depressing the seed production quality. However, neither conventional nor biocontrol product are available on the market to control this disease. In this study Pseudomonas PA14H7, a bacteria isolated from potato rhizosphere, was selected as a potential antagonist agent against Dickeya. In order to understand the mechanism involved in this antagonism we managed to identify the main active(s) molecule(s) produced by PA14H7. In that way, cell-free supernatant (CFS) of PA14H7 cultures were extracted and analyzed by LC-MS, GC-MS and NMR. We have correlated biological activity in extracted CFS-PA14H7 to the presence of 7-hydroxytropolone (7-HT) complexed with iron. Even if this molecule is produced by other Pseudomonas and mostly known for its antibacterial and antifungal activities, it is the first description of its involvement as an effective molecule against pectinolytic bacteria. We have synthesized 7-HT in order to determine the real amount produced by PA14H7 and to compare its activity at the same concentration with that of CFS-PA14H7. This study aims to understand the origin of the antagonist activity of PA14H7 as a potential biocontrol agent against potato blackleg.

Background: Accurate diagnosis of the differentially aggressive fungus Leptosphaeria maculans and Leptosphaeria biglobosa causing Blackleg in crucifers is crucial. Available markers were designed decades ago which may become ineffective due to the ever evolving nature of the fungus, requiring the development of more precise molecular markers. Methods: The whole genomes of available isolates belonging to this two species were aligned using progressive MAUVE tool, species specific genomic regions were extracted and species specific primers were designed from the sequences that encode for effector proteins. Results: Three (Lm1, Lm2 and Lm5) and two (Lb3 and Lb3’) primer sets specifically detected the isolates of target species in PCR based assay, of which the primers Lm5 and Lb3’ were multiplexed for detection of Leptosphaeria maculans and Leptosphaeria biglobosa, generating PCR amplicons of 230 and 834 bp, respectively from a single PCR reaction. The markers were highly sensitive and were able to amplify target species from crude ‘pseudothecia and ascospores suspension’ without requiring DNA extraction. Conclusions: These markers, solitarily or in combination, designed from species specific genomic segments will serve as precise, sensitive and rapid detection of Leptosphaeria maculans and Leptosphaeria biglobosa species and will be helpful for surveillance, management and transboundary quarantine of the devastating disease.