Antifungal activity of cinnamon, clove, and pepper rosemary essential oils against Colletotrichum siamense and their vapor phase effects on guava anthracnose and postharvest quality

Anthracnose is the most devastating fruit disease affecting guava worldwide. The increasing restrictions on the use of synthetic fungicides, particularly during postharvest stages, call for innovative strategies to protect fruits and ensure global food security. Thus, this study aimed to compare pre- and post-inoculation vapor phase treatments of cinnamon (CIN) ( Cinnamomum cassia ), pepper rosemary (PEP) ( Lippia sidoides ), and clove (CLO) ( Syzygium aromaticum ) essential oils (EOs) with synthetic fungicide on guava anthracnose and postharvest quality. Additionally, in vitro assessments were made for EOs action on Colletotrichum siamense mycelial growth, conidial germination, hyphae morphology and membrane integrity, while monitoring the development of early infection structures on treated guava fruits 24 h after inoculation. PEP and CLO exhibited the strongest inhibitory effects on mycelial growth, whereas CIN was more effective in inhibiting conidial germination. While all EOs severely disrupted hyphae morphology, only PEP caused pronounced membrane damage. In contrast to CIN, CLO and PEP vapor phase reduced anthracnose severity in inoculated guavas after seven days of storage, although PEP also induced phytotoxic symptoms. Tebuconazole fungicide treatment showed the greatest reduction in lesion diameter and, together with CLO, delayed weight loss, softening, color change, soluble solids accumulation, and the decline in titratable acidity in guava. A higher rate of appressorial formation was observed in fruits treated with water and CIN compared to CLO and PEP. These findings demonstrate the promising potential of CLO vapor phase as an alternative strategy for postharvest management of guava anthracnose and provide new insights into the EOs antifungal modes of action.