Penicillium digitatum is the causal agent of green mold, a primary postharvest disease of citrus fruits. This study evaluated the efficacy of a novel photoactive chitosan–riboflavin bioconjugate (CH-RF) to control green mold in vitro and in lemon fruit. The results showed total inhibition of P. digitatum growth on APDA supplemented with CH-RF at 0.5% (w/v) and a significant reduction of 84.8% at 0.25% (w/v). Lemons treated with CH-RF and kept under controlled conditions (20 °C and 90–95% relative humidity) exhibited a noteworthy reduction in green mold incidence four days post-inoculation. Notably, these effects persisted, with all treatments remaining significantly distinct from the control group until day 14. Furthermore, CH-RF showed high control of green mold in lemons after 20 days of cold storage (5 ± 1 °C). The disease incidence five days after cold storage indicated significant differences from the values observed in the control. Most CH-RF treatments showed enhanced control of green mold when riboflavin was activated by white-light exposure. These findings suggest that this novel fungicide could be a viable alternative to conventional synthetic fungicides, allowing more sustainable management of lemon fruit diseases.

Orange trees (Citrus × sinensis (L.) Osbeck) are the third-most cultivated citrus fruit species in Chile. In recent years, several trees in three orange orchards of ‘Lane late’ and ‘Fukumoto’ cultivars grafted on ‘Robidoux’ trifoliate orange (Poncirus trifoliata (L.) Raf.) have shown chlorosis, canopy reduction, wilting, root necrosis, defoliation, and plant death symptoms. This study aims to characterize the morphological symptoms observed in diseased orange trees in central Chile and identify the fungal pathogens that are involved. Isolation and morphological characterization of the pathogens were conducted by using different culture media. A total of 53 isolates were obtained, morphologically characterized and 12 isolates were selected for molecular identification. The isolates were identified using ITS, TEF-1α, and RPB2 regions. Two Fusarium species complexes were identified, Neocosmospora (Fusarium) solani (FSSC) and F. oxysporum (FOSC), based on >99% identity. Pathogenicity tests were conducted on young orange seedlings under greenhouse conditions. Results indicated that two months post inoculation, trifoliate orange seedlings displayed root rot symptoms such as necrosis, vascular discoloration, and wilting. FSSC and FOSC were re-isolated from necrotic seedling roots and identified through a combination of morphological traits and molecular techniques. This is the first detailed report of this disease, attributed to FSSC and FOSC, in orange orchards in Chile. These diagnostic results represent the first step in developing adequate phytosanitary programs for managing this disease.