The potential of metchnikowin, a 26-amino acid residue proline-rich antimicrobial peptide synthesized in the fat body of Drosophila melanogaster was explored to engineer disease resistance in barley against devastating fungal plant pathogens. The synthetic peptide caused strong in vitro growth inhibition (IC50 value ∼1 μM) of the pathogenic fungus Fusarium graminearum. Transgenic barley expressing the metchnikowin gene in its 52-amino acid pre-pro-peptide form under the control of the inducible mannopine synthase (mas) gene promoter from the Ti plasmid of Agrobacterium tumefaciens displayed enhanced resistance to powdery mildew as well as Fusarium head blight and root rot. In response to these pathogens, metchnikowin accumulated in plant apoplastic space, specifying that the insect signal peptide is functional in monocotyledons. In vitro and in vivo tests revealed that the peptide is markedly effective against fungal pathogens of the phylum Ascomycota but, clearly, less active against Basidiomycota fungi. Importantly, germination of the mutualistic basidiomycete mycorrhizal fungus Piriformospora indica was affected only at concentrations beyond 50 μM. These results suggest that antifungal peptides from insects are a valuable source for crop plant improvements and their differential activities toward different phyla of fungi denote a capacity for insect peptides to be used as selective measures on specific plant diseases.

This study aimed to evaluate the ability of Piriformospora indica to colonize the root of Chenopodium quinoa and to verify whether this endosymbiont can improve the growth, performance and drought resistance of this species. The study delivered, for the first time, evidence for successful colonization of P. indica in quinoa. Hence, pot experiment was conducted in the greenhouse, where inoculated and non-inoculated plants were subjected to ample (40%-50% WHC) and deficit (15%-20%WHC) irrigation treatments. Drought adversely influenced the plant growth, leading to decline the total plant biomass by 74%. This was linked to an impaired photosynthetic activity (caused by lower g s and C i /C a ratio; stomatal limitation of photosynthesis) and a higher risk of ROS production (enhanced ETR/A gross ratio). P. indica colonization improved quinoa plant growth, with total biomass increased by 8% (controls) and 76% (drought-stressed plants), confirming the growth-promoting activity of P. indica. Fungal colonization seems to diminish drought-induced growth hindrance, likely, through an improved water balance, reflected by the higher leaf w w and g s .Additionally, stomatal limitation of photosynthesis was alleviated (indicated by enhanced C i /C a ratio and A net ), so that the threat of oxidative stress was minimized (decreased ETR/A gross ). These results infer that symbiosis with P. indica could negate some of the detrimental effects of drought on quinoa growth, a highly desired feature, in particular at low water availability.

We explored the antifungal activity of thanatin, a 21 amino acid synthetic peptide from the hemipteran spined soldier bug Podisus maculiventris, against the mycotoxin‐producing plant pathogenic ascomycete Fusarium graminearum. In vitro germination assays showed complete inhibition of macroconidia germination and mycelia growth by >10 μm thanatin. Moreover, detached leaves of thanatin‐expressing Arabidopsis thaliana plants displayed enhanced resistance towards colonization with F. graminearum. Consistent with this, the plants showed also enhanced resistance of detached leaves to colonization with Botrytis cinerea. The results demonstrate a potential of thanatin for use in plant protection.

Plant systemic resistance induced by natural product is an alternative technique of disease management. Riboflavin (vitamin B2) usually used as abiotic elicitor to improve the plant immunity against different pathogens. This work aimed to explore the efficiency of three riboflavin concentrations (0.5, 2.5, and 5 mM) to enhance resistance toward Tobacco Mosaic Virus (TMV) in tomato plants. Our results showed that exogenous application of 2.5mM riboflavin, 5 days before virus challenge was the most effective concentration, which provided a reduction in disease incidence and disease severity by 80% and 75%, respectively. Furthermore, obtained results were confirmed by using DAS-ELISA test, which showed that concentration 2.5 mM of riboflavin decreased the virus concentrations by 46.4% in treated-inoculated plants. It was remarked that exogenous application of 2.5 mM riboflavin showed a positive effect on some plant growth parameters either in presence or absence of TMV challenge. The plant height and number of leaves per plant were significantly improved in treated-inoculated plants about 30% and in compared to the infected control 78%. In time course investigation, 2.5mM riboflavin treatment reduced the virus symptoms particularly at 9 th day, where after the symptoms become evident. In addition, expression of phenylalanine ammonia-lyase (PAL) and pathogenesis-related protein (PR10), which are the markers of systemic acquired resistance (SAR), were rapidly increased in inoculated-treated tomato from 1-3 days after treatment. Moreover, the results of the biochemical changes analysis revealed that, the levels of the defense markers including peroxidase (PO), and polyphenol oxidase (PPO) were increased four days after of treatment and reached maximum levels at 8 days in the treated-inoculated plants. In conclusion, it could be suggesting that riboflavin exerted a great influence on TMV disease, as indicated by reduction of disease symptoms as well as enhancement of biochemical changes in plant defense against infection with TMV.