The effects of chitosan on mycelial growth and spore germination of Colletotrichum gloeosporioides were investigated on potato dextrose agar (PDA) containing 0%, 0.5%, 1.0%, 1.5%, and 2.0% (w/v) chitosan dissolved in 0.5% acetic acid. Complete inhibition of mycelial growth and spore germination was observed in the medium containing only 0.5% acetic acid. Media containing chitosan were less inhibitory, but the highest concentrations of chitosan, at 1.5% and 2.0%, were more inhibitory than the lower concentrations (0.5% and 1.0%). Chitosan treatment (0.5%, 1.0%, 1.5%, and 2.0%) of mangoes {Mangifera indica) previously inoculated with C. gloeosporioides resulted in a lower rate of disease progression compared with the controls. Chitosan concentrations of 0.5% and 1.0% had stimulatory effects on chitinase and β‐1,3‐glucanase activities. Additionally, chitosan coatings in mangoes delayed ripening and reduced respiration rate, ethylene production, and the loss of weight, ascorbic acid, and total titratable acidity. However, the firmness of mangoes treated at concentrations above 1% caused a perceptible decline in sensory quality.

At the present, the mechanism of chlorophyll degradation in response to ionizing irradiation in harvested fruits have not been examined. To understand the effect of electron beam (E-beam) irradiation on the chlorophyll degrading pathway in relation to chlorophyll degrading enzymes activity, reactive oxygen species (ROS) and antioxidant capacities of harvested mangoes stored at 13 °C for 16 days were studied. E-beam-treated fruit significantly suppressed the activities of chlorophyll degrading enzymes especially pheophytinase (PPH) and chlorophyll degrading peroxidase (Chl-POX) in the late stage of storage. This resulted in the chlorophyll content being maintained. However, E-beam irradiation did not affect the activities of chlorophyllase (Chlase) and magnesium de-chelatase (MD). The respiration rate, ethylene production, ROS accumulation (hydrogen peroxide [H₂O₂] and superoxide radical [O^−.₂]) immediately increased after E-beam treatment, following which they significantly decreased in comparison to the control. E-beam treatment enhanced the fruit’s antioxidant capacity by activating the activities of catalase (CAT) and ascorbate peroxidase (APX) and glutathione (GSH) content, and inactivated the activity of superoxide dismutase (SOD). Further, it did not affect the activity of glutathione reductase (GR) and glutathione disulfide (GSSG), vitamin C content, or total phenolic content. These results imply that E-beam treatment has the potential to delay chlorophyll degradation by suppressing the Chl-POX and PPH activities as well as reduce ROS production via CAT, APX, and SOD activities and GSH content.

The production of pectinase, the major virulence determinant of soft-rot Erwinia species, is controlled by many regulatory factors. We focused on the major regulatory proteins, KdgR, CRP, Pir, and PecS, characterized mainly in E. chrysanthemi, and tested for their presence and function in the control of pectate lyase (Pel) and polygalacturonase (Peh) production in E. carotovora subsp. carotovora. Homologues of kdgR and crp but not of pir and pecS were detected by Southern blot analyses in E. carotovora subsp. carotovora. In fact, KdgR and CRP homologues of E. carotovora subsp. carotovora had high amino acid identities to those of E. chrysanthemi, including a complete match of the hypothetical helix-turn-helix DNA-binding motif. However, in Western blot analyses using anti-Pir (E. chrysanthemi) antibodies, a cross-reacting protein was present in both Erwinia species, although Pel production in E. carotovora subsp. carotovora was not further stimulated by adding plant extract into the medium containing PGA (polygalac-turonic acid) in which hyperinduction by Pir has been reported in E. chrysanthemi EC16. When plasmids that contained each of these regulatory genes from E. chrysanthemi were introduced into E. carotovora subsp. carotovora, Pel production was controlled as predicted from their roles in E. chrysanthemi, except for PecS. PecS exerted a positive control in E. carotovora subsp. carotovora, in contrast to a negative control in E. chrysanthemi. DNA-binding assays demonstrated that KdgR, CRP, Pir, and PecS of E. chrysanthemi and KdgR and CRP homologues of E. carotovora subsp. carotovora could bind to the promoter regions of pel-1, pel-3, and peh of E. carotovora subsp. carotovora. Taken together, KdgR and CRP homologues of E. carotovora subsp. carotovora may regulate Pel and Peh production as in E. chrysanthemi. However, the presence of Pir and PecS homologues in E. carotovora subsp. carotovora was not identified in this study, though these proteins of E. chrysanthemi were functional on the promoter regions of the pectinase genes of E. carotovora subsp. carotovora.