Chitosan Effects on Blackmold Rot and Pathogenic Factors Produced by Alternaria alternata in Postharvest Tomatoes

Abstract

<jats:p>Stem scar application of chitosan inhibited growth and production of pathogenic factors by blackmold rot [<jats:italic>Alternaria alternata</jats:italic> (Fr.:Fr.) Keissl.] in challenged tomato (<jats:italic>Lycopersicon esculentum</jats:italic> Mill.) fruit stored at 20 °C for 28 days. Blackmold lesions were visible within 4 days of inoculation in control fruit, compared with &gt;7 days in chitosantreated fruit. Macerating enzyme activity (polygalacturonase, pectate lyase, and cellulase) in the tissue in the vicinity of the lesions was &lt;50% in chitosan-treated fruit compared with control fruit. Chitosan also inhibited production of oxalic and fumaric acids (chelating agents) and host-specific toxins such as alternariol and alternariol monomethylether by the fungus. The pH of the infected tissue decreased from 4.7 to 4.0 in the control fruit, the optimum for polygalacturonase activity, while the pH of chitosan-treated fruit remained at 4.6. In addition, chitosan also induced production of rishitin (a phytoalexin) in tomato tissue. Such chitosan-pathogen-host interactions may be exploited in the control of postharvest pathogens of fresh fruit and vegetables.</jats:p>

Changes in Phenolic Acid Content During Alternaria alternata Infection in Tomato Fruit

“…The pathosystem Alternaria ‐tomato is well documented and we observed the classical blackmold lesions in inoculated tomatoes, indicating the active infection of the fruit 4 days after inoculation. This finding agrees with previous experiments in our lab in which tomato fruits were infected with the same strain of A. alternata (Troncoso et al., 2005; Troncoso‐Rojas et al., 2005) and with other experiments in which harvested tomatoes were inoculated with A. alternata (Reddy et al., 2000).…”

Inhibitory effect of chitosan on growth of the fungal phytopathogen, Sclerotinia sclerotiorum, and sclerotinia rot of carrot

“…1). These results were similar to previous findings on the antifungal activity of chitosan against several other fungal pathogens, such as Aspergillus parasiticus (Cota-Arriola et al 2011), Geotricum candidum (El-Mougy et al 2012), Alternaria alternata (Reddy et al, 2000), Fusarium solani and Sclerotium rolfsii (Eweis et al 2006). Several complex mechanisms were proposed in these previous studies to explain the antifungal activity of chitosan.…”

Alternaria alternata (Black Rot, Black Spot)

“…In previous studies, it was shown that application of chitosan affects growth, morphology, and toxin production by A. alternata f. sp. Similarly, Reddy et al (2000) reported that stem scar application of chitosan inhibited the development of A. alternata on tomatoes stored at 20°C for 28 days by 34%, and reduces production of pathogenic factors by the fungus, such as cell wall-degrading enzymes (polygalacturonase, pectate lyase, and cellulose), organic acids, and host-specific toxins responsible for fungal penetration and host tissue damage. Similarly, Reddy et al (2000) reported that stem scar application of chitosan inhibited the development of A. alternata on tomatoes stored at 20°C for 28 days by 34%, and reduces production of pathogenic factors by the fungus, such as cell wall-degrading enzymes (polygalacturonase, pectate lyase, and cellulose), organic acids, and host-specific toxins responsible for fungal penetration and host tissue damage.…”