Penicillium citrinum-infused Biochar and externally applied auxin enhances drought tolerance and growth of Solanum lycopersicum L. by modulating physiological, biochemical and antioxidant properties

Drought stress is a critical issue in agricultural crops as it can affect crop development, growth, physiological processes and yield. To meet nutritional needs amid rapidly dwindling water resources, it is crucial to adopt precise and efficient strategies through various amendments. Organic treatments such as biochar and the growth hormone auxin (IAA) can play a vital role in this regard. However, it is necessary to refine the existing amendment strategies to attain improved outcomes. Therefore, the present study used Penicillium citrinum-Loaded Biochar (PBC) with and without IAA as amendments under no drought stress in tomato plants. The effects of PBC and IAA on the tomato plants have been examine using several physiological, morphological and biochemical parameters. Results showed that plants sprayed with various doses (0, 10 ppm, 20 ppm, 40 ppm) of IAA and 3.0% (w/w) PBC increased root length (11.11 cm), shoot length (17.88 cm), plant height (38.12 cm), and leaf surface area (40.77 cm²). The highest increase in root fresh weight was 9.5 g, shoot fresh weight was 17.11 g, plant fresh weight was 25.44 g, while the root dry weight was 9.01 g, shoot dry weight was 15.99 g, and plant dry weight was 22.45 g was determined after the synergistic application of PBC and IAA. The proline contents (160.77µmol g^-1FW), total soluble sugar (45.33µmol g^-1FW ), chl a (9.99 mg g^-1 FW), chl b (4.88 mg g^-1 FW), and carotenoids (8.88 mg g^-1 FW), SOD (3.88 mmol g^-1 FW), POD (7.66 mmol g^-1 FW), and CAT (3.91 mmol g^-1 FW), whereas relative water content and electrical conductivity were increased to 48.88% and 30.11% in T6. The H₂O₂ and MDA were decreased to (6.11 µmol/g FW) and (0.29 ± 0.20 µmol/g FW) respectively in T6 as compared to T1. In conclusion the combination of PBC and IAA is an effective, and eco-friendly way to meliorate the growth, biochemical, physiological, and antioxidant enzyme activities of tomato plants under drought stress.