Impacts of Preharvest Treatment with Salicylic Acid and Melatonin in Suppressing Gray Mold (Botrytis cinerea Pers.) in Bell Pepper

Salicylic acid (SA) and melatonin (MT) are recognized as growth regulators and antioxidants in fruits and vegetables. This study examined the impact of foliar SA (0, 1.5, and 2.5 mM) and MT (0 μM as control, 100 μM foliar application, and 100 μM irrigation) on Botrytis cinerea in bell pepper (Capsicum annuum Cv. California Wonder). Treatments were administered pre-fungal infection (2-leaf stage), with one pre-flowering and two post fruit-set applications. Inoculation occurred at flowering, 3 days post-flowering, and 6 days post-flowering. Both SA and MT significantly affected plant growth, leaf and fruit drop, and enzymatic activities in Botrytis-infected plants. 100 μM MT foliar application increased chlorophyll b content, while 100 μM MT irrigation raised phenylalanine ammonia-lyase (PAL) enzyme activity compared to control. SA elevated H₂O₂ levels, PAL and polyphenol oxidase enzyme activities, total dry matter, plant weight, fruit firmness, and plant height in infected pepper plants compared to control. The 1.5 mM SA concentration notably enhanced plant height, fruit firmness, weight, PAL, and superoxide dismutase enzyme activities. This study underscores the potent synergy of SA and MT in bolstering bell pepper resilience against B. cinerea.