Preharvest treatment with Bacillus velezensis HIII11 modulates cell wall dynamics and ripening-related processes in...

The commercial strawberry fruit (Fragaria × ananassa Duch.) is highly perishable due to rapid softening and increased susceptibility to fungal pathogens during ripening and postharvest storage. Plant growth-promoting bacteria (PGPB) have gained increasing attention as a strategy to enhance crop performance and disease tolerance, although their capacity to modulate fruit metabolism and cell wall dynamics in relation to host-pathogen interactions remains unclear. This study evaluated the effects of preharvest inoculation of strawberry plants (cv. 'San Andreas') with Bacillus velezensis HIII11 on fruit quality attributes, cell wall traits, and responses related to Botrytis cinerea. Fruits from inoculated plants showed no significant changes in pH, titratable acidity, or total sugars, but exhibited increased accumulation of phenolic acids, flavonoids, and carotenoids, accompanied by enhanced antioxidant capacity. Alcohol-insoluble residues (AIRs) from treated fruits displayed reduced swelling capacity and limited fungal growth in vitro, suggesting modifications in cell wall architecture. Analysis of pectin side-chain metabolism revealed increased neutral sugar content and downregulation of FaAra1 and FaβGal4, together with differential expression of genes associated with homogalacturonan remodeling (upregulation of FaPME1 and downregulation of FaPLB). In addition, detached leaves from inoculated plants showed reduced B. cinerea infection, and their AIRs restricted fungal growth in vitro. Cell-free culture filtrates of HIII11 also inhibited fungal growth in vitro and attenuated postharvest disease severity when applied to fruits. Collectively, these results suggest that preharvest treatment with B. velezensis HIII11 modulates certain ripening processes and cell wall-related properties in strawberry fruit, with potential implications for host-pathogen interactions.