Growing plants with friendly fungi
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.
Lush growth: Brussels sprout seedlings are grown in compost in modular units before transplant to the field. Image: C. Thornton
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 (ref 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.
Trichoderma is a natural biocontrol agent. Top left panel shows complete loss of lettuce biomass due to the pre-emergence lettuce pathogen Sclerotinia sclerotiorum compared to control, top right, to which T. hamatum (GD12 strain) has been added. Bottom left shows damage to lettuce by post-emergence pathogen Rhizoctonia solani and control by T. hamatum, bottom right. Image: C. Thornton
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 (ref 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 (see 'Field works' below).
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.
A sprout seedling prior to field transplant. Green material around the root is the sporulating Trichoderma fungus. Image: C. Thornton
"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 (ref 3, ref 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 (ref 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."
The trial is in line with M&S' Plan A, its environmental and ethical programme, where the retailer is committed to working towards their fruit, vegetables and salads being 75% pesticide residue-free by 2015.
Simon Coupe, M&S Technologist says as part of their Plan A commitment, they want M&S to become the world’s most sustainable retailer by 2015. "The project with the University of Exeter and the BBSRC is an example of how we are progressing towards achieving this, and we are very proud to have worked closely with both parties that has resulted in this interesting development in agriculture.
"The results that we have seen so far in growth trials will revolutionise how we farm," he says. "If we can harness this technology, we will get healthier plants and greater food production by using less fertiliser, water and plant protection products and building a future for farming"
M&S is also committed to working with its suppliers to improve water efficiency and encourage good water stewardship.
Image shows the positive growth effect of adding the Trichoderma treatment (centre strips) compared to untreated sprouts (sides) after growth in the field for two weeks.
Image: C. Thornton
- Precise Detection and Tracing of Trichoderma hamatum 382 in Compost-Amended Potting Mixes by Using Molecular Markers (external link)
- The beneficial endophyte Trichoderma hamatum isolate DIS 219b promotes growth and delays the onset of the drought response in Theobroma cacao
- An immunological approach to quantifying the saprotrophic growth dynamics of Trichoderma species during antagonistic interactions with Rhizoctonia solani (external link)
- 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
- Tracking fungi in soil with monoclonal antibodies (external link)
- US EPA on Trichoderma