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Plant probiotics: developing an evidence base

Over the last five years a University of Queensland (UQ) research team, lead by Prof. Susanne Schmidt, has been working with farmers to understand how bacteria and fungi in soil can help, or hinder, crop growth.

Good bacteria and fungi can help plants defend themselves against pathogens, acquire essential resources, and become more resilient against stressors such as drought, heat, insects or other pests, soil toxicity and nutrient limitations. Encouraging these organisms with probiotic products could lead to higher yield, obtained using fewer agri-chemicals.

In 2016 Prof. Schmidt’s team published foundational research in Scientific Reports where they demonstrated that inoculation of sugarcane with Burkholderia bacteria resulted in beneficial changes in gene expression, physiology and morphology. Scanning and transmission electron microscopy at Microscopy Australia’s UQ facility were used to examine the bacterial cultures used for the inoculation, and the colonisation of the root surface.

Discoveries like this have lead to a boom in plant probiotic products. However, there is a lack of know-how of where microbial products are best suited, and where alternative or complementary practices are more effective, such as using composts with rich microbial communities, or improving agronomic practices in the first place. “I would argue that many plant probiotics on sale at present do not deliver the promised benefits, potentially depriving our farmers of genuine products developed and tested with scientific rigour. Companies selling effective products are competing with those who just have a good marketing pitch” says Prof. Schmidt.

This is because in Australia, manufacturers are not currently required to provide evidence that their product can actually help crops. This also raises concerns about biosafety: importers can claim there aren’t pathogens in the bottle, without hard proof.

In response, the UQ researchers are teaming up with industry partners to improve product effectiveness, transparency and, hopefully, regulation in the Australian market through scientific testing of microbial products. Their research challenges the ‘one size fits all’ approach to crop probiotics in Australia, and aims to advance the design of effective crop probiotics.

Recently they tested commercial probiotics at both Wide Bay Seedlings, one of Australia’s largest horticulture nurseries, and at a North Queensland sugarcane farm in collaboration with Herbert Cane Productivity Services Limited (HCPSL). They found that the commercial products either did not help the seedlings, or the microbes wouldn’t take hold in the soil. “Unfortunately, probiotic products do not always deliver on their promises. Scientifically valid experimentation needs more emphasis – that is, in relevant settings, over several years and across multiple regions and soils,” Professor Schmidt says.

Following these experiments, the team is now taking a deeper look at the traits of microbes and their potential applications. “We identified numerous microbes with beneficial traits and are testing them for their potential as crop probiotics. The second line of research is to work out how microbes can best be formulated into efficient products,” Professor Schmidt says. For example, in collaboration with Meat & Livestock Australia, they are exploring naturally occurring, beneficial soil microbes to guide practices that ensure soil fertility to ensure long-term sustainability of grazing lands.

As part of this they are contributing to the Australian Microbiome Initiative, a project to map the ecological community of microorganisms inhabiting Australia to create a unique, publicly accessible reference that will enable planners to better manage our environment. It also aims to reduce Australia’s biosecurity risks and increase awareness of potential agricultural and mineral hazards and opportunities.

Published on: Feb 19, 2021