ICL-Royal Holloway Study: Seaweed research for plant parasitic nematodes.

We recently caught up with Tamsin Williams to find out more how her PhD research has progressed. In this first part we focus on the issue of Plant Parasitic Nematodes in Turfgrass.

What was the title of your PhD research and where did you do the work?

Tasmin: “Plant Parasitic Nematode Infection in Turf: Novel Approaches for Management using Seaweeds. My main supervisor was Professor Alan Gange from School of Biological Sciences at Royal Holloway, University of London. The work had an Industrial supervisor; Dr Andy Owen, International Technical Manager at ICL, and was a BBSRC iCASE studentship.”

So the focus is plant parasitic nematodes (PPNs) for turf, did you get an impression of how large a problem this is for the industry?

Tasmin: “Yes, I completed an industry questionnaire chapter which allowed me to quantify that, and basically there is a recognition across the industry of the issue, but most respondents did not see it as one of the key problems facing turf managers. However, for the few turf managers out there where PPNs are an issue – they are searching desperately for the right solution to implement. It is a big problem for them at that time.”

So why look at seaweeds as a mechanism for management of the problem?

Tasmin: “We were looking for a sustainable solution for the PPNs in turf, and actually, there was quite some anecdotal evidence for some seaweed types having a positive effect on the problem.

My industrial supervisor at ICL (Dr Andy Owen) had run some small-scale trials with alkaline extracted seaweeds giving very positive outcome. Hence the development of the project. This approach was completely vindicated whilst researching for our published meta-analysis paper (Williams, T. et al., 2021.

Evaluating the use of seaweed extracts against root knot nematodes: A meta-analytic approach. Journal of Applied Soil Ecology 168 1-8) which showed certain seaweed extracts could help control root knot nematodes in some crops, but the effects were dependent on seaweed type; Ascophylum nodosum seaweed extracts had the greatest control effect, and alkaline extraction versions seemed to have been the most studied.

The results did seem to be variable depending on the PPN type and crop group, so not 100% success for all PPNs or in all crops, but still very positive.”

What were your key experimental findings?

Tasmin: “My pot-based trials using alkaline extracted Ascophylum nodosum demonstrated significant reductions (P<0.01) in PPNs from seaweed applications (three applications at label rate at 21-day intervals), but these trials were in a fairly controlled environment.

Things got more complicated when I took the research into the field. Over the course of three field trials – I did see reductions in PPN numbers from the same seaweed application schedule, but the natural variability of PPNs I measured meant the results did not always demonstrate a significant reduction.

However, on balance we reduced PPNs and certainly significantly lowered the variability, as we published in the European Turfgrass Society Conference paper. (Williams, T. et al., 2020. Ascophylum nodosum extract use on plant parasitic nematode abundance and diversity on a golf green. Rasen 3. 84-85). I think there is clear evidence of efficacy of the method, and with greater replication and trial site selection it could have been much clearer.”

What was the mode of action, how was an alkaline seaweed extract working? Did you investigate that?

Tasmin: “The mode of action will be multi-faceted, but we showed in one experiment how applications of alkaline extracted seaweeds can up-regulate defence genes and defence signalling pathways to potentially allow the plant to defend better against PPN attack.

This was essentially an elicitor response. Allowing the plant to display a range of defence mechanisms. This work was completed on a model plant species (not turfgrass), so there needs to be an element of caution when translating this response to turf species – but I suspect it is highly likely (especially looking at the current areas of research being carried out on the benefits of seaweed applications). A second mode of action was the slowing of the rate of hatching from PPN egg masses.

There was still some hatching of juvenile nematodes but a delayed hatching or a more spread hatching period could allow the plant to better prepare for defence or reduce the overall impact of the PPN infection.”

What is best advice for a turf manager who suspects they have a PPN problem or are managing turf with a history of PPN issues.

Tasmin: “Firstly, monitor and measure the severity of the problem, it is important to get a positive identification of the issue and the species involved. So, collect samples and send off to a Turf Disease Centre and have the turf properly assessed and the nematode species and populations counted.

Secondly, from the work I have completed, use an Ascophylum nodosum seaweed (I exclusively used the SMX product from ICL) with an alkaline extraction and make preventative applications at recommended rate in the period leading up to the key stress periods. My trial work showed positive results following three or four applications at 21-day intervals. I tested greater than recommended rate applications – and they did not seem to add any benefit, but perhaps more frequent applications at standard rate would be useful (however this was not tested).

Of course, it also makes sense to try and reduce the stress the turf is under, to provide greater turf resilience, for example by raising height of cut a little, if possible, by spreading wear, managing moisture in the rootzone and ensuring the plant is not deficient in any nutrients etc.”

PhD encompasses a lot of work, were there other areas to highlight from outside the main-focus of Plant Parasitic Nematodes?

Tasmin: “Yes, I completed an industry questionnaire to highlight some issues which was interesting. It used an innovative system of ranking questions called Q-methodology so allowed modelling of responses – it showed turf industry people were broadly split into 3 groups which was fascinating.

The three groups were ‘Solution-focused – negative thinkers’, ‘Progressive, positive thinkers’ and ‘Acquisition-centered traditionalists’. All groups identified the importance of finding sustainable management options, but these would be implemented at different key stages depending upon the group identity.

There was generally a positive attitude towards biostimulant based management tools, but again the recognition of their importance in a magement programme was different across the groups. It did come across that the industry would take on more sustainable
approaches to management – if they can be clearly demonstrated to work and provide an acceptable level of surface performance.

The Acquisition-centered traditionalists were generally more focused on surface performance in their answers.

There was also a positive trend towards the requirement for more sustainable-centered research to help guide turf managers. The questionnaire provided some valuable and interesting insight and could be worth focusing on completely for a separate article.”

Really interesting, what else?

Tasmin: “There were a number of smaller scale research trials, within the main body of the PPN work. I think four of these would be of interest here.

1.  I showed clearly that applications of alkaline extracted Ascophylum nodosum significantly increased plant rooting. This was very clear for Lolium perenne in particular. We also saw a change in root architecture with the same applications, more branching and more fibrous rooting. However, this was from pot-based trials, and care is always needed translating results from pot-based trials to an applied turf situation. For my field trials on mature turf – I did not measure significantly increased rooting – although there were trends towards greater root biomass. Measurement of rooting in the field is actually quite tricky to do consistently and robustly. It takes a lot of time, and care and I’m not sure the simplistic methodology sometimes employed is that reliable.
2. I also measured mycorrhizal root infection, and applications of alkalineextracted Ascophyllum nodosum significantly increased root infection by naturally occurring mycorrhizae, which was really positive. Better mycorrhizal infection should confer many benefits to the plant, certainly acquisition of some nutrients like phosphorus, and will help under droughting conditions. As an interesting point – we saw less benefit when a combination of commercial mycorrhizal powder and seaweed was applied. The seaweed seemed to work better and provide greater levels of infection with the natural mycorrhizae in the soil than with an applied mycorrhizal powder application which provided a lower rate of root infection – it would have been really nice to follow this up but is a prime example of not having time to follow every avenue of research and leaving some questions unanswered for future research to pick up.
3. One result that surprised me was that in the field trials I didn’t see any improved plant quality benefits, from applications of seaweed extract, in terms of better turf colour or turf growth, at least that I measured. However – all the trials were on well managed turf that received fertilisers and a good level of management, so perhaps this would have been difficult to separate out any plot-based responses coming just from the seaweed applications. Some existing research does show improved plant quality traits, such as crop yield – but Turfgrass can be a difficult crop to assess for quality.
4.  I did some work on entomopathogenic nematodes. These are the ones that might be used to help manage insect larvae as pests in the rootzone. There is a species used to help manage chafer grubs and a species used to help manage leatherjackets in the turf.
   I wanted to check that seaweed applications had no effect if these applications overlapped. The results were very clear. I completed a serial dilution test – so starting with very dilute extract and doubling concentration in sequence. In each case I saw no ill-effect from the seaweed extract – these entomopathogenic nematodes stayed alive and were tested as viable. So clearly even at quite a strong concentration the seaweed extract is not having a direct control upon the live nematode.”

What did you miss from your thesis? Was there something more you wished you could have done?

Tasmin: “There are always unanswered questions and areas you would like to do more research. For me the Covid lockdowns meant I could not continue with more in-field research, it would have been great to have done another season of field trials on a more PPN susceptible site. Also, I could have looked in more detail at the relationship between seaweed applications and the rhizosphere microbiome, in terms of any changes to the environment and the biology there. That would have been really interesting, and I suspect really complicated.”

So what does the future hold? Some more turf research, I hope?

Tasmin: “Not quite, although I have really enjoyed the turf aspect to the research, and the opportunity of the research grant and the industrial support from ICL. I have recently accepted a position as Assistant Editor working for the Frontiers in Plant Science Journal. I will be working with the publication process for research papers in this area, something I am really looking forward to.”