Plant immunity inducers: from discovery to agricultural application

While conventional chemical fungicides directly eliminate pathogens, plant immunity inducers activate or prime plant immunity. In recent years, considerable progress has been made in understanding the mechanisms of immune regulation in plants. The development and application of plant immunity inducers based on the principles of plant immunity represent a new field in plant protection research. In this review, we describe the mechanisms of plant immunity inducers in terms of plant immune system activation, summarize the various classes of reported plant immunity inducers (proteins, oligosaccharides, chemicals, and lipids), and review methods for the identification or synthesis of plant immunity inducers. The current situation, new strategies, and future prospects in the development and application of plant immunity inducers are also discussed.

A Polysaccharide of Ganoderma lucidum Enhances Antifungal Activity of Chemical Fungicides against Soil-Borne Diseases of Wheat and Maize by Induced Resistance

Ganoderma lucidum polysaccharide (GLP), which is the primary active ingredient in G. lucidum, has been widely used in functional food and clinical medicine. However, it is rarely reported in the prevention and control of plant diseases. In this study, we found that the GLP can increase the germination rates and seedling heights of maize and wheat. We also found that the combination of GLP and chemical fungicides as a seed coating chemical compound has a control effect of more than 75% on the primary soil-borne diseases of the wheat and maize growing areas in both greenhouse and field trials. Furthermore, the combination of GLP and chemical fungicides prolongs the lasting period and reduces the application dosage of the chemical fungicides by half. In addition, GLP seed dressing could increase the resistance-related gene expression of the TPS and WRKY53 in maize and WMS533, NbPR1a, and RS33 in wheat. The combination of GLP and low-dose chemical fungicides proved to be an effective way to effectively prevent wheat sharp eyespot, root rot, and maize stalk rot in the wheat and maize continuous cropping areas in the North China Plain and to reduce pesticide use and increase crop yield.

Beneficial effect of Achromobacter insolitus MB20 and manures in reducing Pythium aphanidermatum disease in cucumber

The increased global livestock production, such as chickens, cows, goats, and rabbits causes increased animal waste in both liquid and solid forms. The utilization of animal manures are considered as a beneficial way to minimize the livestock waste problems. Application of manure is advantageous to the soil nutrient balance, soil structure and moisture-holding capacity, and facilitates environmental protection. A combination of biocontrol agent of Achromobacter insolitus MB20 and manures was studied as alternative to chemical fungicides to protect crop from diseases without damaging the environment and human health. The chemical fungicides cannot be used continously and do not represent a sustainable method control. Result showed that an application of A. insolitus alone reduced cucumber damping-off as high as 60%, and in combination of A. insolitus with chicken manure was 80%, goat manure 70%, cow manure and rabbit urine 65%. The in vitro test indicated that A. insolitus inhibited P. aphanidermatum growth by 28%. This antagonist bacterium also produced extracellular enzyme of protease and cellulase with proteolytic index (PI) value was 1.4 and cellulolytic index (CI) value was 1.7. An application of A. insolitus with chicken manure resulted the best combination and the most effective in reducing of cucumber damping-off.

Antifungal Activity of Hyptis spicigera Methanol Leaf Extract and Flavonoid Fraction

Control of plant fungal diseases using synthetic fungicides continue to cause major problems to human health and the entire ecosystem. The aim of this research was to investigate the phytochemical and antifungal properties of Hyptis spicigera methanol leaf extract and flavonoid fraction on Aspergillus and Fusarium species, with a view to uncovering effective bio-fungicides for development as substitutes to chemical fungicides. Phytochemical screening revealed the presence of sterols and triterpenes, cardiac glycosides, flavonoids, tannins and alkaloids. The quantitative analysis showed that saponin (690 mg/g GAE), phenolics (220 mg/g GAE) and flavonoids (140 mg/g GAE) were found to be in high concentration. The antifungal effects of H. spicigera methanol extract on F. graminearum (21 mm) was significantly (p<0.05) higher than the control fungicide (Mancozeb). Similarly, the flavonoid fraction was more effective on A. parasitic (18 mm) than the control fungicide used. The extract and fraction exhibited MIC with range 3.13-12.5 mg/mL and MFC 6.25-12.5 mg/mL, indicating promising antifungal efficacies against A. flavus and F. graminearum. Our findings have revealed that H. spicigera flavonoid rich fraction has potential for development as effective bio-fungicide to control plant fungal diseases of the Aspergillus and Fusarium species.

Electrospun Polymer-Fungicide Nanocomposites for Grapevine Protection

Nowadays, diseases in plants are a worldwide problem. Fungi represent the largest number of plant pathogens and are responsible for a range of serious plant diseases. Esca is a grapevine disease caused mainly by fungal pathogens Phaeomoniella chlamydospora (P. chlamydospora) and Phaeoacremonium aleophilum (P. aleophilum). The currently proposed methods to fight esca are not curative. In this study, polymer composites based on biodegradable polymer containing chemical fungicides with antifungal activity were successfully prepared by electrospinning. The obtained materials were hydrophobic with good mechanical properties. In vitro studies demonstrated that the fungicide release was higher from PLLA/K5N8Q fibrous mats (ca. 72% for 50 h) compared to the released drug amount from PLLA/5-Cl8Q materials (ca. 52% for 50 h), which is due to the better water-solubility of the salt. The antifungal activity of the fibrous materials against P. chlamydospora and P. aleophilum was studied as well. The incorporation of the fungicide in the biodegradable fibers resulted in the inhibition of fungal growth. The obtained materials are perspective candidates for the protection of vines from the penetration and growth of fungal pathogens.