Growing plants with friendly fungi

21st Jul 2011

Natural symbiosis can boost crop growth in dry spells and reduce chemical use.

A hot, dry summer might be an enticing prospect for beach and barbeque lovers, but for food growers the lack of rainfall in spring 2011 and high summer temperatures were predicted to hit harvests and lead to higher food prices – raising the cost of that barbeque no matter how pleasant the weather.

Climate change may mean that these dry and hot conditions will become more common in the UK, so researchers are looking at novel ways to make plants more tolerant of dry spells.

Dr Chris Thornton and colleagues at the University of Exeter are examining whether adding a safe and harmless fungus to compost boosts the growth and proliferation of crops' roots which can help them grow using less water. Not only that, trials currently underway with a supplier to a major supermarket brand are investigating whether the plants exposed to the fungus can be grown in the absence of fertiliser too. 

"So far we've shown the growth promotion effect in lettuce grown in the glasshouse – in the absence of fertiliser you still get an amazing growth increase with a five-fold improvement in root matter," says Thornton. "This is the first time we know of that it's been tried on brassica [broccoli and sprouts] plants in the field."

Even better, previous studies have shown that the fungus has properties as a natural biocontrol agent of pathogenic fungi and could reduce the need for synthetic fungicides (1).

Root of the matter

The method of boosting root growth is simple. The fungus, T. hamatum (GD12 strain), is a free-living soil fungus that feeds on organic matter. The fungus is cultured in wheat bran which is added to the compost in which brassica seedlings are first planted and it is here that root growth flourishes. After a period of growth, the seedlings are transplanted to the field for further growth. This is a common planting technique for many crops resulting in a highly compatible method for growers in the UK and across the world.

The field trials are at an early stage, but early indications show a striking effect after just two or three weeks. "We have dug up fungus treated versus untreated plants grown next to each other and there is a noticeable difference in root mass and the size of leafy green matter," says Thornton.

Thornton says the technique also appears to improve drought tolerance. "As it happens the field trials we are running at the moment coincide with one of the driest Mays in Lincolnshire, so this may explain in part why we have better growth in the Trichoderma-treated plants." Other studies have shown a delay in plants' drought response when exposed to Trichoderma (2).

Together is better

The field trial is a collaboration between university, grower and retailer. Manor Fresh Ltd in Lincolnshire supplies Marks & Spencer's with brassicas such as broccoli and sprouts, and M&S has been working closely with its supplier in developing the technique.

Furthermore, a BBSRC Responsive Mode grant recently awarded to Thornton and Exeter colleague Murray Grant is supporting laboratory-based work that will attempt to unravel the molecular basis of the plant-growth-promotion phenomenon.

"It's a nice tie in between industry and fundamental research back at Exeter," he says. "We know the fungus produces a water soluble compound that stimulates plant growth… but why and how does the plant respond to this stimulus?"

The association between the fungus and the plant doesn't appear to be symbiotic because there's nothing in it for the fungus that we can so far see – this particular strain of Trichoderma (GD12) does not grow inside the plant's roots, instead it lives around them in a zone called the rhizosphere (3,4). But it is apparent that somehow the fungus is changing the way that the plant perceives its environment and causes changes in the plants' chemistry that increase root and shoot growth.

Thornton says the plant growth phenomenon has been known for a decade or so (5). But it's the move in recent years to adopt more sustainable agricultural systems in line with modern food security agendas that has brought the use of organisms like Trichoderma (ref 6) back into focus.

"There is potential to use it everywhere," says Thornton, who says his group is the only one in the UK who still works on the plant-growth-promoting aspects of organism. "With the move to sustainable mechanisms of control these organisms are right up the agenda again. This is the first time there's been an interaction between a UK university department and plant growers to replace costly fossil fuel fertilisers with a strain of Trichoderma that stimulates plant growth and at the same time acts as a biocontrol agent of root diseases."

References

1. Precise Detection and Tracing of Trichoderma hamatum 382 in Compost-Amended Potting Mixes by Using Molecular Markers

2. The beneficial endophyte Trichoderma hamatum isolate DIS 219b promotes growth and delays the onset of the drought response in Theobroma cacao

3. An immunological approach to quantifying the saprotrophic growth dynamics of Trichoderma species during antagonistic interactions with Rhizoctonia solani

4. Production of a monoclonal antibody specific to the genus Trichoderma and closely related fungi, and its use to detect Trichoderma spp. in naturally infested composts

5. Tracking fungi in soil with monoclonal antibodies

6. US EPA on Trichoderma

 

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