Carotenoids are the principal pigments in the loquat. Although the metabolic pathway of plant carotenoids has been extensively investigated, few studies have been explored the regulatory mechanisms of loquat carotenoids because knowledge of the loquat genome is incomplete. The chromoplast-specific lycopene β-cyclase gene (CYC-B) could catalyze cyclization of lycopene to β-carotene. In this study, the differential accumulation patterns of loquat with different colors were analyzed and virus-induced gene silencing (VIGS) was utilized in order to verify CYC-B gene function. Using a cloning strategy of homologous genes, a CYC-B gene orthologue was successfully identified from the loquat. At a later stage of maturation, CYC-B gene expression and carotenoids concentrations in the ‘Dawuxing’ variety were higher than in ‘Chuannong 1-5-9′, possibly leading to the difference in pulp coloration of loquat. Interference of CYC-B gene expression in the loquat demonstrated clear visual changes. The green color in negative control fruits became yellow, while TRV2-CYC-B silenced fruits remained green. CYC-B gene expression and total carotenoid content in the pulp decreased by 32.5% and 44.1%, respectively. Furthermore, multiple key genes in the carotenoid metabolic pathway synergistically responded to downregulation of CYC-B gene expression. In summary, we provide direct evidences that CYC-B gene is involved in carotenoid accumulation and coloration in the loquat.

Blue mold caused by Penicillium italicum (P. italicum) is a major postharvest disease in citrus fruits. Lipoic acid (LA) is a potent antioxidant with biological activity that was evaluated for its inhibitory effects on P. italicum and citrus blue mold using in vitro and in vivo experiments. The results demonstrated that LA effectively suppressed the mycelial growth and spore germination of P. italicum. LA increased hydrogen peroxide levels, compromising cell membrane integrity and leading to enhanced membrane permeability, as indicated by the increased relative conductivity and decreased protein and total sugar contents in P. italicum mycelia. Furthermore, LA delayed disease progression in citrus fruits infected with P. italicum through increasing total phenol and flavonoid contents and enhancing the activities of phenylalanine ammonia lyase, polyphenol oxidase, superoxide dismutase, and peroxidase in citrus peel. Overall, LA exhibited strong antifungal activity against P. italicum and improved citrus fruit resistance to blue mold, highlighting its potential as a natural postharvest disease control agent.