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Biology, and by extension agronomy, has been traditionally built around the concept of classification – providing a framework that understands organisms and biological systems as a collection of individual parts. This means that there has often been a focus on understanding the individual parts, but there is limited appreciation for the interactions between them. Yet, by understanding the biology of the whole system we are able to get a deeper understanding of how the plant works – enabling us to utilise its natural processes to increase its levels of resilience, which vastly reduces crop loss and helps to keep input costs down.
In recent years, the concept of ‘systems biology’ has become increasingly mainstream. It upends the traditional perspective by employing a holistic approach to understanding the complex interactions within biological systems. By viewing the system as a whole, one can observe important properties that belong to the system, but not to any individual part – these are known as ‘emergent behaviours’.
An example of an emergent behaviour would be a starling murmuration. If you were to isolate the movements of a single starling, then its behaviour would not make sense. But, when you look at the movements of the starlings together then you understand that the individual is part of a wider system – one that serves to protect the group, and each individual within it, from predators. So, by viewing at the level of the system, we are able to get a better understanding of the individual.
The same is true for plants. At present, in agronomy we often view plants both as a collection of individual parts, and as a whole individual that is separate from the plants, animals and microorganisms that immediately surround them. This leads to advice that focuses on distinct areas of the plant or growing ecosystem, without consideration of its wider impacts.
With the traditional approach, independent programmes are created for foliar pests, root pests, foliar diseases, root diseases, fertilisation and growing media selection. By not considering the impact that each of these programmes has across the whole plant and ecosystem, practices can be followed that are directly antagonistic to one another. This can lead to increased costs because more inputs are required to solve problems created by other actions. A classic example is the over-application of nitrate fertiliser, which promotes attractive fast green growth. Yet, this growth attracts pests and provides them with an easily accessible and nutrient-rich feeding source, necessitating subsequent pesticide applications.
This can be combated with a holistic approach. This approach encourages us to understand the plant as a collection of parts that continually interact with one another – as well as with the plants, animals and microorganisms that immediately surround them. By doing this, we holistically consider the wider effects of our agronomic inputs – not just on the target area. This enables us to employ practices that are complementary to one another, making them significantly more effective while reducing input costs.
How does holistic growing manage disease?
The key to controlling disease using holistic methods lies in understanding that a plant is not a sterile environment – nor would we want it to be. Instead, it is a complex structure hosting a variety of ecological niches that house communities of microbes, with which it is in continual interaction. If managed correctly, these communities can be exceptionally beneficial to plant health, but if managed poorly, they can be extremely damaging.
The key microbiomes of a plant are the rhizosphere (the area around the roots) and phyllosphere (the above ground parts of the plant). Both are colonised by microbes that will perform different functions, and these can either be beneficial, neutral or negative to the plants health. The potential benefits, which are emergent behaviours of the system, are exceptionally wide ranging.
A healthy microbiome will exclude or even attack pathogenic microbes in the space. In addition to this, these microbes can release nutrition within the proximity of the roots or shoots, reduce signalling chemicals that guide steady growth and limit potential entry points for pathogens, as well as inducing biochemical systemic resistance across the whole plant – meaning beneficial root microbes will provide protection to plant shoots and vice-versa. An unhealthy microbiome, on the other hand, lacks these beneficial microbes and instead harbours pathogenic ones that can attack the plant to cause disease.
Our aim, then, is to maximise the presence of beneficial microbes and limit the presence of harmful ones. Conveniently, as this is also the plant's aim, they possess a wide range of processes that enable them to cultivate healthy microbiomes—such as the release of metabolites to nourish the microbes. This allows for the recruitment and propagation of a friendly microbial community and the repulsion and combating of pathogens.
The systems approach is therefore useful because to do this the plant must be provided with all of the correct resources to be able to undertake these processes. This means providing the correct nutrition for both the plant and the beneficial microbes, the correct environmental conditions for both root and shoot growth, and a healthy surrounding ecosystem that the plant can recruit beneficial microbes from instead of pathogens.
Look out for part two on how to use holistic growing practices – coming soon. For more information, please contact Jack Haslam on 01903 256856 or email jack.haslam@fargro.co.uk.