Synergistic regulation of yield and fruit quality in plum through combined application of mycorrhizal fungi and a tri-species leaf extract bio-stimulant

Despite the established benefits of mycorrhizal fungi and botanical biostimulants, their synergistic effects on fruit crop quality and productivity remain insufficiently characterized. This study evaluated the combined application of three mycorrhizal species ( Rhizophagus irregularis , Serendipita indica , and Rhizophagus fasciculatus ) with a tri-species custard apple–citrus–guava leaf extract (CCG @1%) on five-year-old ‘Satluj Purple’ plum trees under subtropical field conditions. A factorial randomized block design with eight treatment combinations and three replications per treatment was used to assess fruit morphological traits, yield components, phosphorus content, and key biochemical attributes, including antioxidant activity, total phenolics, and flavonoids. Among the treatments, Rhizophagus fasciculatus combined with CCG @1% (RfLE₁) consistently outperformed the control and single-factor treatments. RfLE₁ increased fruit yield from 34.99 to 64.86 kg tree⁻¹, enhanced fruit phosphorus content from 0.13% to 0.41%, and elevated antioxidant activity from 80.73% to 89.65%. It also raised total soluble solids from 8.45 to 15.60 °B, increased flavonoid content from 124.33 to 191.07 mg QE 100 g⁻¹, slightly improved fruit weight (31.82 to 34.78 g), and reduced titratable acidity from 1.05% to 0.55%. Synergy analysis indicated that RfLE₁ produced effects on yield, phosphorus nutrition, and multiple quality traits that exceeded the expected additive contributions of the individual mycorrhiza and leaf extract treatments. These findings suggest that integrating R. fasciculatus with a standardized CCG leaf extract can substantially enhance productivity and nutraceutical quality in ‘Satluj Purple’ plum, while highlighting the need for multi-season and economic evaluations before broad-scale commercial adoption.