Abstract
A growing world population and an increasing demand for greater food production requires that crop losses caused by pests and diseases are dramatically reduced. Concurrently, sustainability targets mean that alternatives to chemical pesticides are becoming increasingly desirable. Bacteria in the plant root microbiome can protect their plant host against pests and pathogenic infection. In particular, Streptomyces species are well-known to produce a range of secondary metabolites that can inhibit the growth of phytopathogens. Streptomyces are abundant in soils and are also enriched in the root microbiomes of many different plant species, including those grown as economically and nutritionally valuable cereal crops. In this review we discuss the potential of Streptomyces to protect against some of the most damaging cereal crop diseases, particularly those caused by fungal pathogens. We also explore factors that may improve the efficacy of these strains as biocontrol agents in situ, as well as the possibility of exploiting plant mechanisms, such as root exudation, that enable the recruitment of microbial species from the soil to the root microbiome. We argue that a greater understanding of these mechanisms may enable the development of protective plant root microbiomes with a greater abundance of beneficial bacteria, such as Streptomyces species.
Highlights
Cereal crops, or “cereals”, are plants belonging to the grass family Poaceae that are grown and harvested primarily for their edible grain [1]
An analysis of the microbial composition of this soil led to the isolation of the bioactive strain Streptomyces griseoviridis; this was used to formulate the broad-spectrum biofungicide Mycostop®, which is active against a number of crop diseases, including wheat head blight caused by Fusarium species [70]
Increasing amounts of phenolic-related compounds are exuded by A. thaliana roots at later developmental stages and these have been shown to correlate with an increased number of microbial transcripts related to antimicrobial production, including streptomycin produced by Streptomyces species, independent of changes to bacterial abundance [131]
Summary
“cereals”, are plants belonging to the grass family Poaceae that are grown and harvested primarily for their edible grain [1]. Many pesticides can lead to both acute and chronic toxicity in humans and they are increasingly being shown to cause wide-spread damage to the wider ecosystem by impacting non-target organisms, such as pollinator species, and through the pollution of soil and water systems [18,19,20]. These non-target effects can extend to reducing the diversity of beneficial microbial species in the soil, which can in turn release pathogen populations from competition and increase the chances of pathogen invasion [21]. It is being realised that the microorganisms living within soil and in close association with plant roots can make large contributions to plant health and could be engineered as biocontrol agents
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