Diversity and Plant Growth‐Promoting Potential of Duckweed‐Associated Bacteria on <scp> <i>Wolffia globosa</i> </scp> Biomass Production and Nutritional Quality

Wolffia (Lemnoideae) is recognised as a nutritional superfood with increasing interest in commercial cultivation. Its growth and biomass quality are influenced by abiotic factors and duckweed-associated bacteria (DAB) that support nutrient cycling, stress tolerance and metabolism. This study assessed DAB diversity and their effects on Wolffia growth to select effective plant growth-promoting bacteria (PGPB) and elucidated beneficial plant-microbe interactions. A total of 108 isolates, representing 66 species from 41 genera across four phyla, were obtained from duckweeds collected in six provinces of Thailand. The culturable DAB community showed high taxonomic diversity, dominated by the phylum Pseudomonadota, particularly Alphaproteobacteria. The isolates, along with the known PGPB of Spirodela polyrhiza, were evaluated for growth promotion in axenic Wolffia globosa using co-cultivation. Six PGPB enhanced growth by 54.67%-77.75% without reported pathogenicity. Several PGPB originally isolated from S. polyrhiza also showed growth-promoting effects on Wolffia. Large-scale co-cultivation demonstrated that Pseudomonas toyotomiensis W5-11 most effectively increased dry weight and chlorophyll content (3.18- and 2.75-fold, respectively). All selected isolates produced indole-3-acetic acid (IAA), siderophores and solubilised phosphate. Correlation analysis revealed that IAA production was associated with protein accumulation. These findings suggested that PGPB represent promising biofertilisers that enhance Wolffia productivity and nutritional quality through various mechanisms.