There’s something in the water (potential)

There’s something joyful about catching a wave!

On our regular summer beach holidays to Kaka Point in the Catlins, my family’s favourite pastime is boogie-boarding. We don our wetsuits, slap on some sunblock, grab our boards and hit the beach whenever we can. There is something very primeval about pitting yourself against the waves. The exhilaration of catching a good ride which takes you all the way to the shore is palpable. The joy on people’s faces as they hurtle at the forefront of a powerful wave, barely in control, is often quite startling. Catching waves is a matter of skill, experience and luck. Body size helps as well. On an average day with reasonable waves my younger sons tend to get longer rides than me, they have the skill required and being lighter, they can make the most of the power of the waves. On days with smaller waves, being smaller can help a lot with catching waves (although experience is also important in making the most of the limited wave force). Still, boogie-boarding doesn’t really work well in those conditions. On days with big waves; wild, surging and, frankly, scary walls of water, then extra size is a bonus as you can stand up to the drag and not be knocked about by the sheer power of the ride. One of the great aspects of boogie-boarding, surfing, sea-kayaking and so on, is that while you remain much the same from day to day, the sea conditions are almost always different from day to day. How effective you will be, how many waves you will catch, how long the rides will be is largely dependent on factors other than you.

Sclerotinia infected lettuce
Sclerotinia infected lettuce

A dependence on habitat conditions is central to many elements of ecology. At the macro level, plants and animals behavioural and physiological responses are often influenced by factors such as weather, mineral deficiencies, presence of predators and competitors, fragmentation of habitat and so on. At the micro level, it turns out to be much the same. Sclerotinia is a fungus that can attack plants and causes white mold. Sclerotinia can persist in soil for long periods and causes many problems for crop plants, especially vegetables. Controlling this pathogen is extremely important for horticulture. One bioprotection tool that we can use are fungi from the Trichoderma genus. This fungus is often found in soil where it breaks down plant and fungus material. Trichoderma has been shown to be very effective in controlling Sclerotinia in experimental trials. However, results when used by growers in their crops has been highly variable which has limited the uptake of other growers in using Trichoderma themselves. Understanding, and potentially removing, this variation in success would allow this bioprotection tool to become far more widely used (and reduce our reliance on chemical solutions to white mold control).

Apothecia under cabbage seedling (Sclerotinia in soil germinate to produced apothecia)

Eirian Jones, with colleagues Damien Bienkowski and Alison Stewart, investigated the potential of water potential to be an important part of how Trichoderma performs. Soil water potential is made up of several components. The two that are most relevant to soil fungi are matric potential and osmotic potential. Matric potential is determined by the size and type of soil particles and influences water moving into a fungus by pores through capillary action. Osmotic potential is determined by soil organic and inorganic solutes in the water and influences the rate at which water moves into an out of a fungus through membranes. Eirian prepared suspensions of Trichoderma in six different levels of water potential and added to individual soil samples. Sclerotinia were added to these experiments a day later and their growth measured after two and four weeks. Eirian found some clear results (published in Annals of Applied Biology). Trichoderma growth, unlike Sclerotinia, decreased with decreasing matic and osmotic potentials. The more water challenged the external environment was, the harder Trichoderma found it to grow and the more Trichoderma struggled to control Sclerotinia. Matric potential seemed to play the larger role compared to osmotic potential. Broadly speaking, one of the reasons that Trichoderma may be so variable in its performance in protecting crops is that the ground may be too dry for it survive and grow to a point at which it can control Sclerotinia. This could be good news for Trichoderma as now we know which conditions will aid its growth, we can look at adding moisture when we inoculate soils, and this research found that there was variation between different strains (indicating that there is potential to select for more effective strains). So once again we see that the success of individuals depends on how they respond to the habitat around them and that this is also driven by changes in the habitat.


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