Current technologies to control fungal diseases in postharvest papaya (Carica papaya L.)

Effect of cinnamon essential oil/γ-cyclodextrin inclusion complex on papaya quality and shelf-life

BACKGROUND

Papaya, a highly nutritious and economically significant fruit, is susceptible to infections caused by phytopathogenic fungi. Cinnamon essential oil, derived from Cinnamomum cassia (CC), shows promise in preserving papaya due to its antifungal properties. However, CC is volatile, sensitive to environmental factors, and carries a strong aroma. γ-Cyclodextrin (γ-CD) is known for encapsulating hydrophilic molecules, shielding them from environmental influences, reducing odor, and enabling controlled release due to its unique channel structure. This study aimed to tackle these challenges by preparing and characterizing an inclusion complex of CC with γ-CD (CC-γ-CD), and subsequently evaluating its efficacy in preserving papaya fruits.

RESULTS

Analyses, including Fourier-infrared, powder X-ray diffraction, thermal gravity analysis, differential scanning calorimeter, and scanning electron microscopy, revealed successful encapsulation of CC components within the γ-CD cavity. Evaluations of the CC-γ-CD complex's impact on papaya fruit shelf life and quality showed notable enhancements. Fruits treated with CC-γ-CD inclusion complex at a dose of 10 g kg-1 exhibited a 55% extension in shelf-life, evidenced by reduced disease severity index compared with untreated fruit in the same storage conditions. Detailed physicochemical and bromatological assessments highlighted significant improvements, particularly in fruit treated with CC-γ-CD inclusion complex at a dose of 10 g kg-1.

CONCLUSION

The application of CC-γ-CD inclusion complex at 10 g kg-1 extended the shelf-life of papaya fruit, significantly and markedly improved the overall quality. These findings underscore the potential of the CC-γ-CD inclusion complex as an effective preservative for papaya, offering a promising solution for its postharvest management and marketability. © 2024 Society of Chemical Industry.

Design and Synthesis of Eugenol Derivatives Bearing a 1,2,3-Triazole Moiety for Papaya Protection against Colletotrichum gloeosporioides

A series of 19 novel eugenol derivatives containing a 1,2,3-triazole moiety was synthesized via a two-step process, with the key step being a copper(I)-catalyzed azide-alkyne cycloaddition reaction. The compounds were assessed for their antifungal activities against Colletotrichum gloeosporioides, the causative agent of papaya anthracnose. Triazoles 2k, 2m, 2l, and 2n, at 100 ppm, were the most effective, reducing mycelial growth by 88.3, 85.5, 82.4, and 81.4%, respectively. Molecular docking calculations allowed us to elucidate the binding mode of these derivatives in the catalytic pocket of C. gloeosporioides CYP51. The best-docked compounds bind closely to the heme cofactor and within the channel access of the lanosterol (LAN) substrate, with crucial interactions involving residues Tyr102, Ile355, Met485, and Phe486. From such studies, the antifungal activity is likely attributed to the prevention of substrate LAN entry by the 1,2,3-triazole derivatives. The triazoles derived from natural eugenol represent a novel lead in the search for environmentally safe agents for controlling C. gloeosporioides.

G-site residue S67 is involved in the fungicide-degrading activity of a tau class glutathione S-transferase from Carica papaya

Thiram is a toxic fungicide extensively used for the management of pathogens in fruits. Although it is known that thiram degrades in plant tissues, the key enzymes involved in this process remain unexplored. In this study, we report that a tau class glutathione S-transferase (GST) from Carica papaya can degrade thiram. This enzyme was easily obtained by heterologous expression in Escherichia coli, showed low promiscuity toward other thiuram disulfides, and catalyzed thiram degradation under physiological reaction conditions. Site-directed mutagenesis indicated that G-site residue S67 shows a key influence for the enzymatic activity toward thiram, while mutation of residue S13, which reduced the GSH oxidase activity, did not significantly affect the thiram-degrading activity. The formation of dimethyl dithiocarbamate, which was subsequently converted into carbon disulfide, and dimethyl dithiocarbamoylsulfenic acid as the thiram degradation products suggested that thiram undergoes an alkaline hydrolysis that involves the rupture of the disulfide bond. Application of the GST selective inhibitor 4-chloro-7-nitro-2,1,3-benzoxadiazole reduced papaya peel thiram-degrading activity by 95%, indicating that this is the main degradation route of thiram in papaya. GST from Carica papaya also catalyzed the degradation of the fungicides chlorothalonil and thiabendazole, with residue S67 showing again a key influence for the enzymatic activity. These results fill an important knowledge gap in understanding the catalytic promiscuity of plant GSTs and reveal new insights into the fate and degradation products of thiram in fruits.

Elicitation of Fruit Fungi Infection and Its Protective Response to Improve the Postharvest Quality of Fruits

Fruit diseases brought on by fungus infestation leads to postharvest losses of fresh fruit. Approximately 30% of harvested fruits do not reach consumers’ plates due to postharvest losses. Fungal pathogens play a substantial part in those losses, as they cause the majority of fruit rots and consumer complaints. Understanding fungal pathogenic processes and control measures is crucial for developing disease prevention and treatment strategies. In this review, we covered the presented pathogen entry, environmental conditions for pathogenesis, fruit’s response to pathogen attack, molecular mechanisms by which fungi infect fruits in the postharvest phase, production of mycotoxin, virulence factors, fungal genes involved in pathogenesis, and recent strategies for protecting fruit from fungal attack. Then, in order to investigate new avenues for ensuring fruit production, existing fungal management strategies were then assessed based on their mechanisms for altering the infection process. The goal of this review is to bridge the knowledge gap between the mechanisms of fungal disease progression and numerous disease control strategies being developed for fruit farming.