Plant growth-promoting Pseudomonas strains modulate potato tuberization signalling and development

Plant growth-promoting rhizobacteria (PGPR) can influence plant development through hormone signalling, nutrient mobilization, and activation of defence pathways. While individual bacterial strains can enhance plant performance, microbial consortia may generate complementary or synergistic effects that remain poorly understood, particularly with respect to crop developmental signalling. Potato (Solanum tuberosum), the most important dicot food crop globally, represents a suitable model for investigating how beneficial microbes influence tuber development. In this study, we investigated the effects of two well-characterized PGPR strains, Pseudomonas protegens CHA0 and P. simiae WCS417, applied individually or in combination, on two potato cultivars ('Mandel' and 'Désirée') under long-day conditions. Confocal microscopy confirmed rapid root colonization by both strains within 24 h of inoculation. Metabolomic profiling of bacterial exudates revealed distinct metabolic signatures for the two strains and non-additive metabolite patterns when cultured together, suggesting metabolic interactions within the bacterial consortium. Plant responses were cultivar dependent, with bacterial treatments influencing vegetative growth and selected tuber quality traits, including starch and ascorbic acid levels. Gene expression analyses revealed strong induction of the tuberization regulator StSP6A in roots, with up to 5-fold increased expression following P. protegens and combined inoculation, accompanied by activation of jasmonic acid-related signalling pathways. Together, these results indicate that interactions between beneficial Pseudomonas strains can influence potato development through coordinated effects on root architecture and signalling pathways associated with tuberization and defence.