Using an electronic nose to detect decay in tree roots

Following on from my initial post about using electronic noses to pick up decay within a tree (which I suggest you glance over before reading this), I thought I’d visit further literature on the subject but with more of a refined focus. In this instance, we’ll be looking solely at the ability for electronic noses (specifically the PEN3 electronic nose) to detect decay within the rooting environment of trees. As was elucidated to in my previous post, the PEN3 can pick-up decay from root systems in the field setting, though here we can observe how a slightly earlier study fared in terms of its efficacy upon root samples inoculated in the laboratory and stored beneath different types of soil.

Because not all fungi will colonise the root system of a tree, the fungal species chosen in this study were Armillaria mellea, Ganoderma lucidum, and Heterbasidion annosum (a shame that Meripilus giganteus was not included). These three species can be considered principal root-rotters. These fungi were, once cultivated and made into mycelial plugs, brought into contact with healthy root samples (1-3cm in diameter and 2-10cm in length) of adult trees of the species Aesculus hippocastanum, Cedrus deodara, Liquidambar styraciflua, Platanus x hispanica, and Quercus robur. Such roots, complete with fungal inoculum, were then buried beneath sourced urban soils (and also ‘professional’ nursery soils), in order to reflect what soils the PEN3 would need to ‘sense’ through if it were to be applied in the ‘field’, and a period of time was given for the mycelium to begin colonising the root samples and. After a year, the samples were ready for testing. Then, following a set of complex processes that only a three-page methodology could ever fully encapsulate, it was time to look at the results (which are equally as complex, so I’ll do my best to simplify them).

What the researchers found was that the ability for the PEN3 to detect decay in the roots of different tree species by different wood decay fungi, all whilst under different soil types, was quite good (and more notably for urban soils) – see the below graphs. The nose was able to differentiate between healthy and decayed samples of root tissues with a high degree of variance between the two, meaning that there was little to no scope for ‘confusion’ between healthy and decayed root samples. Similarly, it was able to significantly differentiate between the fungal agents causing the decay in certain instances, and particularly in the cases where the fungi-tree relationship would naturally occur in the ‘field’. For example, the nose could identify (but not significantly differentiate between the two) oak roots colonised by A. mellea and G. lucidum – both are natural pathogens of the species. Granted, this trend wasn’t conslusive, as the nose couldn’t differentiate between healthy and A. mellea-infected samples in horse chestnut. The second set of graphs outlines the data collected with regards to differentiating between the decay from different fungal species.

PEN3rootdecay
The ability of the PEN3 to discriminate between healthy (green) and infected (blue) tree roots for A. hippocastanum (a), C. deodara (b), L. styracuflua (c), and Q. robur (d).

Under the urban soils, the nose worked more effectively, and this is considered to be because soils also emit their own VOCs, and professional nutrient-rich soils will have a ‘stronger’ emission. However, these professional soils still didn’t stop the PEN3 from identifying whether a root was decayed or healthy.

PEN3fungirootdecay
How the PEN3 differentiated between decay from different fungi (A. mellea [blue], G. lucidum [red], H. annosum [grey], and healthy [green], on the tree species A. hippocastanum (a), C. deodara (b), L. styraciflua (c), P. x hispanica (d), and Q. robur (e).
Evidently, some work is required in ensuring the PEN3 becomes very able to differentiate between the decay from different fungi on different tree species (and under different soils), though even from the graphs above we can see how there is, by-and-large, some degree of differentiation between the readings (as shown by the clusters, which infrequently overlap, but are sometimes close together). The decay from different fungi in Cedrus deodara appears to be particularly well differentiated, whilst decay in Aesculus hippocastanum is less so. Of course, it’s mainly a calibration and sensory game, and if the PEN3 can be accentuated in sensory ability then there’s certainly scope for this to be a very effective field diagnostic test for decay of root systems, and all whilst not having to damage the tree in any manner. Compiled with the more recent results of the PEN3 being able to work in the ‘field’, it’s an interesting piece of technology to keep an eye on.

Source: Baietto, M., Pozzi, L., Wilson, A., & Bassi, D. (2013) Evaluation of a portable MOS electronic nose to detect root rots in shade tree species. Computers and Electronics in Agriculture. 96 (1). p117-125.

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Using an electronic nose to detect decay in tree roots

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