Beneficial Soil Additives Improve Apple Tree Health and Natural Defenses

Greg Howard
27th May, 2024

Beneficial Soil Additives Improve Apple Tree Health and Natural Defenses

This reported experiment was designed to compare the effects of two microbial inoculants, Bacillus velezensis FZB42 and Pseudomonas sp. RU47, against a control on apple plants grown in soil either affected by apple replant disease (ARD) or from a healthy grassland.

Image adapted from: Hauschild et al. / CC BY (Source)

Key Findings

  • The study from the Julius Kühn Institute in Braunschweig, Germany, explored eco-friendly methods to combat apple replant disease (ARD) using microbial inoculants
  • Applying Bacillus velezensis FZB42 and Pseudomonas sp. RU47 to apple roots increased the plants' defense compounds, especially in non-ARD soil
  • The inoculants significantly altered the microbial community in ARD soil, reducing harmful bacteria like Enterobacteriaceae on apple roots
Improving soil health and combating plant diseases through eco-friendly methods is a significant focus in sustainable agriculture. One promising approach is the use of microbial inoculants to modulate the soil microbiome, enhancing its disease-suppressive properties. Recent research from the Julius Kühn Institute, Braunschweig, Germany, has provided new insights into how the application of specific microbial strains can benefit apple trees, particularly those affected by apple replant disease (ARD)[1]. ARD is a condition that hampers the growth of new apple trees in soil previously used for apple cultivation. This study investigated the ability of two microbial inoculants, Bacillus velezensis FZB42 and Pseudomonas sp. RU47, to colonize apple root-associated microhabitats and influence the root microbiome. The researchers aimed to see if these inoculants could help mitigate ARD by altering the microbial community in the soil. The study involved growing apple plants in two types of soil: one affected by ARD and another from a grassland area not previously used for apple cultivation. The researchers applied the microbial inoculants to the apple plants and monitored their establishment using selective plating techniques. They also measured the levels of phytoalexins—compounds produced by plants as a defense mechanism—in the roots at different time points (3, 16, and 28 days post-inoculation). Phytoalexins play a crucial role in plant defense against pathogens[2]. The study found that the inoculants increased the phytoalexin content in apple roots, with a more pronounced effect observed in grassland soil compared to ARD soil. This indicates that the apple plants recognized the presence of the inoculants and responded by boosting their defense mechanisms. The researchers also sequenced 16S rRNA gene and ITS fragments from DNA extracted from various soil and root samples 28 days post-inoculation. This analysis revealed significant changes in the fungal community structure (β-diversity) in the root-affected soil and rhizoplane (the root surface). Notably, in ARD soil, the relative abundance of certain bacterial groups, particularly Enterobacteriaceae, was significantly altered by the inoculants. Both Bacillus velezensis FZB42 and Pseudomonas sp. RU47 reduced the relative abundance of Enterobacteriaceae in the rhizoplane of apple trees grown in ARD soil. The study's findings align with previous research highlighting the potential of microbial inoculants to influence plant-associated microbial communities and improve plant health. For example, Pseudomonas jessenii RU47 was previously shown to effectively suppress bottom rot in lettuce by establishing itself as the dominant Pseudomonas population in the rhizosphere and stabilizing the microbial community structure[3]. Similarly, the current study demonstrates that microbial inoculants can modulate the root-associated microbiome of apple trees, potentially offering a sustainable solution to ARD. Moreover, the concept of using microbial inoculants to restore or stabilize the plant microbiome has been discussed extensively in recent literature[4]. Microbial inoculants can induce various beneficial shifts in the plant microbiome, such as increasing microbial diversity, restoring balance after a pathogen-induced disruption, and suppressing harmful pathogens. The current study supports these ideas by showing that the inoculants not only established themselves in the apple root-associated microhabitats but also influenced the microbial community in a way that could benefit the plant. In conclusion, the research from the Julius Kühn Institute provides valuable insights into the potential of Bacillus velezensis FZB42 and Pseudomonas sp. RU47 as eco-friendly solutions for mitigating apple replant disease. By modulating the root-associated microbiome and enhancing the plant's natural defense mechanisms, these inoculants offer a promising strategy for improving soil health and promoting sustainable apple cultivation.

AgricultureBiochemPlant Science

References

Main Study

1) Rhizosphere competent inoculants modulate the apple root-associated microbiome and plant phytoalexins.

Published 27th May, 2024

https://doi.org/10.1007/s00253-024-13181-8

Related Studies

2) Biphenyls and dibenzofurans of the rosaceous subtribe Malinae and their role as phytoalexins.

https://doi.org/10.1007/s00425-023-04228-7

3) In vitro antagonists of Rhizoctonia solani tested on lettuce: rhizosphere competence, biocontrol efficiency and rhizosphere microbial community response.

https://doi.org/10.1111/j.1574-6941.2009.00685.x

4) Microbiome Modulation-Toward a Better Understanding of Plant Microbiome Response to Microbial Inoculants.

https://doi.org/10.3389/fmicb.2021.650610


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