Abstract
Phenazine-1-carboxylic acid (PCA) produced by plant-beneficial Pseudomonas spp. is an antibiotic with antagonistic activities against Phytophthora infestans, the causal agent of potato late blight. In this study, a collection of 23 different PCA-producing Pseudomonas spp. was confronted with P. infestans in potato tuber bioassays to further understand the interaction existing between biocontrol activity and PCA production. Overall, the 23 strains exhibited different levels of biocontrol activity. In general, P. orientalis and P. yamanorum strains showed strong disease reduction, while P. synxantha strains could not effectively inhibit the pathogen’s growth. No correlation was found between the quantities of PCA produced and biocontrol activity, suggesting that PCA cannot alone explain P. infestans’ growth inhibition by phenazine-producing pseudomonads. Other genetic determinants potentially involved in the biocontrol of P. infestans were identified through genome mining in strains displaying strong biocontrol activity, including siderophores, cyclic lipopeptides and non-ribosomal peptide synthase and polyketide synthase hybrid clusters. This study represents a step forward towards better understanding the biocontrol mechanisms of phenazine-producing Pseudomonas spp. against potato late blight.
Highlights
Based on available genome sequences, we identified traits only associated with strains displaying strong in planta biocontrol activity, that may be involved in the biocontrol of P. infestans
Each tuber was evaluated for the severity of late blight symptoms on the exposed side of the cut tuber compared to the controls, and each strain was categorized among three groups according to the results’ average: (1) weak biocontrol activity, (2) intermediate biocontrol activity, and (3) strong biocontrol activity
Based on available genome sequences of the 23 strains used in this study, we looked for possible additional contributors to the biocontrol of potato late blight by phenazineproducing pseudomonads (Figure 5) [23]
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. More than 150 years after the Irish Potato Famine, potato late blight caused by the oomycete Phytophthora infestans still poses a threat to potato production worldwide. Despite efforts invested in breeding programs and genetic engineering to create late blight resistant cultivars, limited success has been obtained. Current control strategies focus mostly on prevention and still heavily rely on the use of chemical pesticides [1,2]. Most potato cultivars of commercial interest are susceptible to late blight, and P. infestans strains are becoming more aggressive and resistant to chemical pesticides such as metalaxyl, a commonly used systemic phenylamide fungicide [3,4]. In the USA and Canada, P. infestans strains US-8
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