Abstract
Biochar has been reported to play a positive role in disease suppression against airborne pathogens in plants. The mechanisms behind this positive trait are not well-understood. In this study, we hypothesized that the attraction of plant growth-promoting rhizobacteria (PGPR) or fungi (PGPF) underlies the mechanism of biochar in plant protection. The attraction of PGPR and PGPF may either activate the innate immune system of plants or help the plants with nutrient uptake. We studied the effect of biochar in peat substrate (PS) on the susceptibility of strawberry, both on leaves and fruits, against the airborne fungal pathogen Botrytis cinerea. Biochar had a positive impact on the resistance of strawberry fruits but not the plant leaves. On leaves, the infection was more severe compared with plants without biochar in the PS. The different effects on fruits and plant leaves may indicate a trade-off between plant parts. Future studies should focus on monitoring gene expression and metabolites of strawberry fruits to investigate this potential trade-off effect. A change in the microbial community in the rhizosphere was also observed, with increased fungal diversity and higher abundances of amplicon sequence variants classified into Granulicella, Mucilaginibacter, and Byssochlamys surrounding the plant root, where the latter two were reported as biocontrol agents. The change in the microbial community was not correlated with a change in nutrient uptake by the plant in either the leaves or the fruits. A decrease in the defense gene expression in the leaves was observed. In conclusion, the decreased infection of B. cinerea in strawberry fruits mediated by the addition of biochar in the PS is most likely regulated by the changes in the microbial community.
Highlights
Biochar, a by-product of pyrolysis, is the subject of many agricultural studies (Lehmann and Joseph, 2009)
We postulated that the changes in the microbiome are essential for the effect of biochar amendment on plant disease resistance and that microbial changes in the rhizosphere lead to (1) a change in the nutrient content of the plant and/or (2) activation and/or priming of plant defense genes
The present experiment revealed that in the presence of biochar, a more severe infection with B. cinerea was observed on the leaves of strawberry plants, while disease symptoms on fruit were reduced
Summary
A by-product of pyrolysis, is the subject of many agricultural studies (Lehmann and Joseph, 2009). For soilless cultivation, biochar has been reported to be beneficial: first, because it can partially replace peat (Blok et al, 2017), and second, because it improves plant-based traits (De Tender et al, 2016b; Nieto et al, 2016). Low concentrations of biochar in growing media have been reported to support disease suppression (Frenkel et al, 2017). Symptoms of airborne diseases caused by pathogens, such as Botrytis cinerea, Colletotrichum acutatum, Podosphaera aphanis, and Leveillula taurica (Elad et al, 2010; Meller Harel et al, 2012; De Tender et al, 2016a,b), as well as soilborne pathogens, such as Pythium, parasitic nematodes, and Fusarium oxysporum (Huang et al, 2015; Frenkel et al, 2017; Jaiswal et al, 2018, 2020), are reduced on the application of biochar to the growing media or soil. No direct toxic effect of biochar on pathogens has been reported (e.g., Huang et al, 2015; Wang et al, 2020), indicating that other mechanisms play a role in disease suppression
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