Evaluating PGPR traits coupling under mutagenesis: A phenotypic and statistical framework for targeted improvement

Understanding the functional coupling between key PGP traits is crucial as PGPR use multiple mechanisms to promote plant growth and nutrition. This study uses UV mutagenesis to generate diversity in Stenotrophomonas maltophilia GZB27, applying a phenotypic statistical framework to evaluate coupling between indole-3-acetic acid production and phosphate solubilization for targeted improvement. UV exposure time inversely correlated with survival; 8.4 minutes achieved the target 5% viability threshold. Significant variation in IAA production occurred among 19 mutants compared to the wild type (18.19 µg/mL): nine hyperproducers (peak in M6, +33.5%; 24.28 µg/mL) and three strains with reduced biosynthesis (e.g., M16, −31.1%; 12.54 µg/mL) were identified. Significant variation in phosphate solubilization was observed among 19 mutants versus wild type (249.00 µg/mL): seven hyper efficient solubilizers (peak in M14: +62.1%; 403.67 µg/mL) and two with reduced capacity (e.g., M6: -50.1%; 124.33 µg/mL) were identified. Three integrated statistical methods were used to evaluate metabolic coupling between phosphate solubilization and IAA production in PGPR mutants. Spearman's correlation (ρ=0.213, p=0.368) revealed no significant population-level relationship, visually confirmed by dispersed data points indicating strain-specific autonomy. Antagonistic profiling quantified a strong functional trade-off via the Antagonism Index (AI), with mutants specializing in high PS (e.g., M3, M17) exhibiting reduced IAA, and vice-versa (e.g., M6, M10); only rare strains such as M4 showed balanced traits. Phenotypic Pleiotropy Modelling found predominantly neutral indices (41% of strains) and no significant trait correlation (Pearson r=0.245, p=0.2983), indicating minimal genetic constraint between traits. This multi-scale evaluation suggested genetically distinct bases governing PS and IAA