Abstract
Reactive oxygen species (ROS) play an active role in plant defense. Polyphenol oxidase (PPO) and peroxidase (POD) participate in the synthesis of phytoalexins. The comparative activities of ROS, including hydrogen peroxide (H2O2), superoxide anions (O2−), and hydroxyl radicals (·OH), against the fungal pathogen Colletotrichum gloeosporioides from papaya fruit were evaluated. The effects of ROS on PPO and POD activities in papaya fruit inoculated with C. gloeosporioides and the development of natural decay in intact fruit were also investigated. ·OH was the most effective in inhibiting conidial germination and mycelial growth of C. gloeosporioides in vitro. However, 20 or 30 mM H2O2 exhibited the best control of the three ROS treatments at ameliorating the disease symptoms associated with the highest levels of PPO and POD activities in papaya fruit. Furthermore, the activities of PPO and POD negatively correlated with the disease index. Overall, H2O2 treatments can induce the resistance of papaya fruit against C. gloeosporioides owing to the enhanced activities of PPO and POD. Treatment with 20 mM H2O2 also significantly reduced the incidence of decay in intact papaya fruit in semi-commercial experiment, which could make it a potential alternative manner to control postharvest disease in papaya fruit.
Highlights
Numerous pathogens exist in the natural environment and result in the substantial loss of crops
Was found to be the at inhibiting germination and mycelial growth diates are most toxiceffective to pathogens, and, conidial they were suggested to be of Co. gloeosporioides of the reactive oxygen species (ROS)
A low amount of H2 O2 may play a central role in the plant defense system, such as mediating the transcription of specific genes that encode PR proteins, inducing the generation of phytoalexins, and enhancing lignification or other defense responses [6,10–12]
Summary
Numerous pathogens exist in the natural environment and result in the substantial loss of crops. The hypersensitive response (HR) is an early defense phenomenon that successfully recognizes pathogens by causing cell death and necrosis to attack pathogen growth [3]. In this phase, significant amounts of reactive oxygen species (ROS), including superoxide anions, hydrogen peroxide (H2 O2 ), and hydroxyl radicals, are produced [4,5]. ROS have been reported to participate in the plant defense systems as antimicrobial byproducts against pathogen infection [5–7]. ROS, H2 O2 , has been suggested to serve as an antimicrobial agent during the plant defense response [5–7]. Et al reported that treatment with 5 mM H2 O2 inhibits the development of inocula from 4-day-old Septoria tritici cultures [8]. Micromolar concentrations of H2 O2 markedly inhibit the germination of Peronospora tabacina, Cladosporium cucumerinum, and Colletotrichum lagenarium spores in vitro [9]
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