Trichoderma longibrachiatum (T6) Peptaibols Inhibiting the Monilia yunnanensis Growth and Inducing Pear Fruit Resistance in Its Infection

Pear fruit brown rot, caused by <i>Monilia yunnanensis</i>, affects pear fruit yields and quality. The present study determined <i>Trichoderma longibrachiatum</i> T6 (T6) peptaibols as a biological control alternative to synthetic fungicides and assessed its efficacy against <i>M. yunnanensis</i> through dual plate culture and surface spraying at different concentrations. T6 peptaibols effectively inhibited <i>M. yunnanensis</i> growth, achieving an 85.99% inhibitory rate at 1250 µg/mL after inoculation on PDA medium for 5 days, and 84.57% control efficacy on pear fruit with the same concentration at 6 days. Treatment with T6 peptaibols significantly decreased the average contents of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), as well as electrolyte leakage, by 31.99%, 27.93%, and 21.00% from days 1 to 9 post-inoculation, respectively, in comparison to the negative control. Additionally, the average antioxidant enzyme activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD) and polyphenol oxidase (PPO) increased by 86.27%, 56.76%, 25.94%, and 47.88%, respectively; the average defense enzyme activities of phenylalanine ammonia-lyase (PAL), lipoxygenase (LOX), chitinase (CHI), and β-1,3-glucanase (β-Glu) increased by 63.00%, 55.70%, 26.19%, and 16.34%, respectively. Moreover, the expression levels of the antioxidant and defense-related genes (<i>CAT</i>, <i>SOD</i>, <i>POD</i>, <i>PPO</i>, <i>CHI</i>, <i>LOX</i>, <i>PAL</i>, <i>β-Glu</i>) were significantly upregulated by 2.80, 2.81, 3.03, 2.79, 3.37, 2.49, 2.73, and 1.83-folds at 3 days after inoculation compared to the negative control. Thus, T6 peptaibols effectively reduced the pathogen infection through growth inhibition and antioxidant defenses, thereby boosting fruit immunity.