Colonization dynamics of Bacillus velezensis TCS001 and its Mechanism of sustained induced resistance against strawberry anthracnose

Strawberry anthracnose caused by Colletotrichum spp. leads to substantial yield losses, and biocontrol using Bacillus velezensis TCS001 offers a promising alternative to chemical fungicides. However, the colonization dynamics, duration of induced resistance, and underlying molecular mechanisms remain unclear. In this study, we constructed a GFP-tagged strain TCS001-GFP, which exhibited growth characteristics and antifungal activity comparable to the wild-type strain. Root drenching with TCS001-GFP resulted in rapid colonization of strawberry roots (peak 8.7 × 10⁶ CFU/g at day 3), leaves (peak 2.1 × 10⁶ CFU/g at day 7), and petioles (peak 1.6 × 10 5 CFU/g at day 5), with stable populations persisting for at least 35 days. TCS001 significantly promoted plant growth, increasing plant height (92.2 %), shoot fresh weight (132.5 %), root fresh weight (317.8 %), and leaf number, accompanied by elevated levels of indole-3-acetic acid (67.5 %), gibberellic acid (7.0 %), and abscisic acid (38.3 %). The bacterium induced systemic resistance against C . siamense , providing strong protection (control efficacy > 92 %) when challenged within 3 days after treatment, but efficacy declined to 9.6 % by day 21. Transcriptome analysis revealed that TCS001 downregulated photosynthesis-related genes while upregulating defense-related genes involved in MAPK signaling, phenylpropanoid biosynthesis, and glutathione metabolism. Time-course qPCR of seven defense-related genes (WRKY23, RPV1, PR-1, PR-1A-like, PR-4-like, NBS-LRR, cytochrome P450) uncovered a coordinated temporal activation indicative of a systemic defense strategy. Collectively, our findings demonstrate that TCS001 colonizes strawberry plants systemically, promotes growth through phytohormone modulation, and induces transient resistance via transcriptional reprogramming. The relatively short protection window highlights the need for optimized application strategies to maximize its biocontrol potential in sustainable strawberry production.