pH-dependent defense responses in eggplant: growth performance and resistance to Verticillium dahliae

Eggplant is a globally important vegetable crop, yet its intensive greenhouse cultivation often leads to soil acidification, which exacerbates the incidence of Verticillium wilt. Verticillium dahliae (V. dahliae) is a major soil-borne pathogen that severely reduces eggplant growth, however, the defense responses of eggplant under different pH conditions and the mechanistic basis underlying pH-mediated resistance are still untouched and unclear. Therefore, the physiological and molecular responses of eggplant to V. dahliae inoculation under two soil pH conditions (5.5 and 6.5 VD/CK) was investigated. Soil pH profoundly influences disease severity and plant defense activation. V. dahliae inoculation at pH 5.5 led to a high disease index of 59.67%, significantly stunting plant growth. In contrast, a near-neutral pH of 6.5 promoted robust plant growth even under pathogen challenge. Defense responses were potentiated at pH 6.5, as evidenced by a significant increase in the activity of key defense enzymes (CAT, PAL, POD, PPO, SOD, β-1, 3-glucanases) and the upregulation of defense-related genes SmeGLU and SmeGPX. Subcellular localization confirmed that this enhanced defense correlated with a stronger nuclear accumulation of defense proteins in inoculated plants at pH 6.5. pH modulates resistance not only by reducing disease severity but also by enhancing transient protein expression and subcellular defense responses. Results demonstrated that a near-neutral soil pH of 6.5 is optimal for priming the eggplant defense system against V. dahliae. These findings reveal a critical link between soil pH and innate immunity in eggplant, offering new avenues for leveraging pH management and defense-related genes for crop improvement.