Role of Reactive Oxygen Species against Pathogens in Relation to Postharvest Disease of Papaya Fruit

Antifungal and elicitor activities of p-hydroxybenzoic acid for the control of aflatoxigenic Aspergillus flavus in kiwifruit

Aspergillus flavus not only reduces kiwifruit production but also synthesizes carcinogenic aflatoxins, resulting in a relevant threat to human health. p-Hydroxybenzoic acid (pHBA) is one of the most abundant phenolics in kiwifruit. In this study, pHBA was found to reduce A. flavus mycelial growth by blocking the fungal mitotic exit network (MEN) and cytokinesis and to inhibit the biosynthesis of aflatoxins B1 and B2. The application of pHBA promoted the accumulation of endogenous pHBA and induced oxidative stress in A. flavus-infected kiwifruit, resulting in an increase in H2O2 content and catalase (CAT) and superoxide dismutase (SOD) activities. Preventive and curative treatments with 5 mM pHBA reduced A. flavus advancement by 46.1% and 68.0%, respectively. Collectively, the antifungal and elicitor properties of pHBA were examined for the first time, revealing new insights into the role of pHBA in the defense response of kiwifruit against A. flavus infection.

Decrypting the multi-functional biological activators and inducers of defense responses against biotic stresses in plants

Plant diseases are still the main problem for the reduction in crop yield and a threat to global food security. Additionally, excessive usage of chemical inputs such as pesticides and fungicides to control plant diseases have created another serious problem for human and environmental health. In view of this, the application of plant growth-promoting rhizobacteria (PGPR) for controlling plant disease incidences has been identified as an eco-friendly approach for coping with the food security issue. In this review, we have identified different ways by which PGPRs are capable of reducing phytopathogenic infestations and enhancing crop yield. PGPR suppresses plant diseases, both directly and indirectly, mediated by microbial metabolites and signaling components. Microbial synthesized anti-pathogenic metabolites such as siderophores, antibiotics, lytic enzymes, hydrogen cyanide, and several others act directly on phytopathogens. The indirect mechanisms of reducing plant disease infestation are caused by the stimulation of plant immune responses known as initiation of systemic resistance (ISR) which is mediated by triggering plant immune responses elicited through pathogen-associated molecular patterns (PAMPs). The ISR triggered in the infected region of the plant leads to the development of systemic acquired resistance (SAR) throughout the plant making the plant resistant to a wide range of pathogens. A number of PGPRs including Pseudomonas and Bacillus genera have proven their ability to stimulate ISR. However, there are still some challenges in the large-scale application and acceptance of PGPR for pest and disease management. Further, we discuss the newly formulated PGPR inoculants possessing both plant growth-promoting activities and plant disease suppression ability for a holistic approach to sustaining plant health and enhancing crop productivity.

Arbuscular mycorrhizal fungus alleviates anthracnose disease in tea seedlings

Tea has been gaining increasing popularity all over the world in recent years, and its yield and quality depend on the growth and development of tea plants [Camellia sinensis (L.) Kuntze] in various environments. Nowadays, biotic stress and extreme weather, such as high temperature, drought, waterlogging, pests, and diseases, bring about much pressure on the production of tea with high quality. Wherein anthracnose, which is the most common and serious disease of tea plants, has earned more and more attention, as its control mainly relies on chemical pesticides. Arbuscular mycorrhizal fungi (AMF), forming symbiosis with most terrestrial plants, participate in plant resistance against the anthracnose disease, which was found by previous studies in a few herbaceous plants. However, there are a few studies about arbuscular mycorrhizal (AM) fungal regulation of the resistance to the anthracnose pathogen in woody plants so far. In this paper, we investigated the effect of AMF on the development of anthracnose caused by Colletotrichum camelliae and tried to decipher the pertinent mechanism through transcriptome analysis. Results showed that inoculating AMF significantly reduced the damage of anthracnose on tea seedlings by reducing the lesion area by 35.29% compared to that of the control. The content of superoxide anion and activities of catalase and peroxidase significantly increased (P < 0.05) in mycorrhizal treatment in response to the pathogen with 1.23, 2.00, and 1.39 times higher, respectively, than those in the control. Pathways of plant hormone signal transduction, mitogen-activated protein kinase (MAPK) signaling, and phenylpropanoid biosynthesis might play roles in this regulation according to the transcriptomic results. Further redundancy analysis (RDA) and partial least squares structural equation modeling (PLS-SEM) analysis found that plant hormones, such as auxin and ethylene, and the antioxidant system (especially peroxidase) were of great importance in the AM fungal alleviation of anthracnose. Our results preliminarily indicated the mechanisms of enhanced resistance in mycorrhizal tea seedlings to the anthracnose pathogen and provided a theoretical foundation for the application of AMF as one of the biological control methods in tea plantations.