Arbuscular Mycorrhizal Fungi and Modern Wheat Varieties (Direct Driller Issue 2 - Article 3)

Arbuscular Mycorrhizal Fungi and Modern Wheat Varieties



Procam have been working with a number of no-till farmers to look at ways of maximising crop yields whilst reducing inputs. One of the key areas which Procam have been looking at is the use of growth promoting bacteria and fungi to help stimulate root development and increase nutrient and water uptake by the crop. One such trial now in its second year, has been looking at the potential of modern varieties of wheat to be colonised by arbuscular mycorrhizal fungi and the benefits of this association.

Approximately 74% of flowering plants form associations with arbuscular mycorrhizal fungi (AMF), which require a plant host to survive, and the colonisation of plant roots by AMF has been shown to have a number of plant benefits, including; increasing plant uptake of nutrients and water, increasing a plants’ tolerance to both biotic (pathogen infection) and abiotic (drought) stresses and improving soil structure through the release of the protein glomalin.

However any current farming practices have depleted the natural levels of AMF in the soil, through the use of some pesticides and fertilisers to which they are sensitive, growing crop species such as oilseed rape, or sugar beet which are non-mycorrhizal and through cultivation practices where their hyphal network is damaged. No-till farming practices are a good environment for the re-development of natural mycorrhizal populations, and we have seen this on our trial farm down in Essex, which has very high background levels of AM fungi.

The trial I conducted on behalf of Procam, wanted to assess not only the ability o modern wheat varieties to be colonised by AM fungi, but also to assess any potential differences in varietal colonisation levels which might help us to be able to identify varieties best suited to the no-till growing system. The trial took place on a farm down in Essex which has been practicing no-till for over 10 years and with soils which had been tested and found to have high background levels of mycorrhizae present within the field.

A total of nine different varieties of wheat, plus the farmers’ own group 4 wheat variety blend were drilled in the autumn of 2016, following lucerne. The wheat was taken through to harvest with assessments made in March, when the plants were tillering and in July just before the crop was harvested, on the level of AMF colonisation seen. Colonisation levels were assessed by staining the wheat roots with a dye which binds to the AMF structures within the root cells, allowing me to visually assess the proportion of the root samples which were colonised.

The images in figure.1 are examples, taken using a microscope showing some AM fungi structures found in stained wheat roots at the assessment timings in March (A) and July (B). AMF structures have been stained dark blue, whilst plant cells remain white/ light blue. The results from the first year of the trial showed us that all the varieties of wheat tested were capable of AMF colonisation, although the levels of colonisation varied between varieties (figure.2). There was an overall increase in the level of AMF colonisation within the wheat roots from March to July and this is likely due to AM fungi becoming more active as temperatures increase and could also explain the lower variability in colonisation levels between varieties in the samples taken in July, as those less mycorrhizal varieties had a chance to ‘catch-up’.

Of all the varieties trialled KWS Bassett and KWS Silverstone appeared to be the most mycorrhizal, with KWS Silverstone having double to five times the proportion of root area colonised, compared to the other varieties at the March sample timing. This gap had reduced by the July sample timing and it was KWS Bassett that had the highest level of colonisation at this timing, although KWS Silverstone still had the second highest level of colonisation, suggesting that these two varieties are potentially the best to grow in no-till systems.

A second year of the trial is currently on-going, with most of the same varieties being tested, to try and see if the results of last year’s trial are replicable. Procam will be at Groundswell this year on 27th-28th June, at stand E5 in the pasture field, where I or my colleagues will be able to give more information out about our work on AMF, including some preliminary results from the second year of the wheat trial and our work with other biologicals, and our other no-till trials.

You can read the Article online which is on Page 6 Of Direct Driller Magazine here: https://issuu.com/directdriller/docs/direct_driller_issue_2/6

 

[Fat hen]

I wonder what (if any) affect the introduction of what is a 'foreign' species of AMF in such high concentrations has upon the soil's own natural MF. In other situation in nature if you introduce a foreign, albeit related, species then it can have a devastating affect on the native species.
I may be barking up the wrong tree here as it may be that AMF are the same species as what it already living in your soil

 

[Clive]

I wonder what (if any) affect the introduction of what is a 'foreign' species of AMF in such high concentrations has upon the soil's own natural MF. In other situation in nature if you introduce a foreign, albeit related, species then it can have a devastating affect on the native species.
I may be barking up the wrong tree here as it may be that AMF are the same species as what it already living in your soil

A good point and I guess no one really knows the answer yet

 

[Chris F]

I wonder what (if any) affect the introduction of what is a 'foreign' species of AMF in such high concentrations has upon the soil's own natural MF. In other situation in nature if you introduce a foreign, albeit related, species then it can have a devastating affect on the native species.
I may be barking up the wrong tree here as it may be that AMF are the same species as what it already living in your soil

I've read quite a few articles on AMF before we have picked the one's in Direct Driller, but not read anything to the above effect. There does seem to be different AMF species that work with different plants. But in the articles about using them as biofertisilers, I've not read anything about species matching. So that's not a definitive answer, but I reckon Dr Iain Gould of Lincoln University might know more, so I'll ask him.

This is worth a read: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4717633/

In it they talk about the issues of adding AMF field scale and they don't mention our issue, not that that's a definitive answer.

Extract:

The production of AMF crude inoculum on a large-scale remains very challenging even though new methods for massive production (IJdo et al., 2011) and seed coating technology (Vosátka et al., 2013) have been developed in recent years (van der Heijden et al., 2015). The main obstacle to the production of an AMF inoculum lies in the obligate symbiotic behavior of AMF, that is, their need to have a host plant for growth and completion of their life cycles. This means that the propagation step must include a phase of cultivation with the host plant that is usually time and space-demanding. As a consequence, the setting up of AMF reference collections also requires methodologies that are rather different and more binding than those used for other microbial collections. Moreover, the absence of a prompt method for assessing whether and to what extent the host plant is colonized by AMF also contributes to making AMF agricultural usability challenging. The management of the high amount of inoculum necessary for large-scale application is also a demanding process. However, AMF inoculation is carried out more easily for plant production systems that involve a transplant stage, since smaller amounts of inoculum are needed.

At a first glance, carrying out an open-field, extensive inoculation treatment could seem technically impractical and economically prohibitive. However, once AMF biodiversity is restored and well-established, and if an AMF-friendly management, such as fall cover cropping (Lehman et al., 2012) and conservation tillage (Säle et al., 2015) is put in place, the AMF community will persist. If no detrimental practices are carried out before and after cultivation, it is known that the biodiverse mycorrhizal hyphal network will remain unaltered and infective in the future. As an alternative to large-scale inoculation, a small-scale approach is also feasible. Taking inspiration from the idea of creating the so-called “fertility islands” (Allen, 1987), AMF inoculation could be limited to small portions of a field, and this would gradually lead to the establishment of a healthy AMF mycelial network, but with reduced costs. This technique would be particularly indicated when the AMF inoculation is aimed at assisting the revegetation of a degraded land, since inoculated fertility islands likely allow native plant species to recover the nutrient impoverished land faster.

Hence, AMF restoration only represents an initial cost that, if the persistence of AM fungi is favored in the soil, could be prorated over the years. As already demonstrated (Gulati and Cummings, 2008; Barr, 2010), AMF inoculation can be economically profitable, in comparison to conventional fertilization, providing substantial savings for growers and for degraded land recovery projects. In order to provide further data to assess AMF inoculation attractiveness, it is important that the end-users should also cultivate an uninoculated portion of their crop, so as to be able to evaluate the cost-effectiveness and beneficial effects on plant fitness due to AMF (Dalpé and Monreal, 2004).

 

[Simon C]

This field was not inoculated with foreign mycorrhizae. Lottie was observing naturally occurring mycorrhizae that had built up over three years of undisturbed lucerne. The wheat was then direct drilled into the lucerne stubble and the living hyphae moved straight onto the the new roots.

The interesting thing is that we have often supposed that modern varieties are not capable of extracting nutrients by the natural system of mycorrhizal colonisation and need to be spoon fed, however this trial proved that they are all perfectly suitable to be used in a biological system.