Camellia japonica flower extracts suppress plant bacterial pathogens via biofilm disruption and virulence inhibition

Bacterial phytopathogens such as Erwinia amylovora and Xanthomonas campestris cause severe economic losses in fruit and vegetable crops worldwide. Their control is increasingly challenging due to limited availability of effective bacteri- cides and the emergence of resistant strains. In this context, there is an urgent need to identify sustainable and environ- mentally friendly alternatives to conventional chemical control strategies. This study evaluates the antibacterial activity of hydromethanolic extracts from Camellia japonica cv. ‘Lipstick’ against these two major bacterial pathogens, exploring potential mechanisms of action and in planta efficacy. Camellia japonica L. is traditionally valued in Eastern medicine for its bioactive compounds, which have diverse pharmacological properties. This study evaluated the antibacterial potential of hydromethanolic leaf and flower extracts from C. japonica cv. ‘Lipstick’ against the phytopathogens Erwinia amy- lovora and Xanthomonas campestris pv. campestris, significant contributors to global agricultural losses. Gas chroma- tography‒mass spectrometry revealed distinct phytochemical profiles, with D-fucose (33.6%), dihydroxyacetone (7.6%), and methoxy-phenyl-oxime (5.7%) predominating in the leaf extracts, whereas the flower extracts contained methoxy- phenyl-oxime (14.1%) and 2,3-dihydro-3,5-dihydroxy-6-methyl-4 H-pyran-4-one (6.3%) as major constituents. The flower extracts exhibited superior antibacterial activity, with minimum inhibitory concentrations (MICs) of 1000 µg·mL− 1 against X. campestris and 1500 µg·mL− 1 against E. amylovora; in contrast, the leaf extracts showed no activity at the tested con- centrations. The flower extract altered bacterial membrane permeability, significantly inhibited biofilm formation (by up to 74%), disrupted mature biofilms, and reduced amylovoran production in E. amylovora by 2.57-fold. In planta assays on Pyrus communis showed a 71% reduction in fire blight severity. Scanning electron microscopy confirmed biofilm disruption and prevention of bacterial adhesion. These findings highlight the potential of C. japonica flower extracts as promising eco-friendly alternatives to conventional antibiotics for managing bacterial plant diseases, offering a potential solution for treating fire blight in pear orchards.