Finding a solution to Fusarium Basal Rot - the onion disease that threatens the staple vegetable

4th Nov 2013

Onions offer a variety of health benefits and are a vitally important horticultural crop. More than 78.5 million tonnes of onions are produced worldwide each year, with an economic value of around £18,673 million. 

But onion crops around the world are being blighted by a disease called Fusarium Basal Rot (FBR). Last year, losses due to FBR were estimated at £11 million in the UK alone. 

“The problem with FBR is that it can affect the root of the onion at any stage in the plant's development, causing seedling death or resulting in the bulb rotting in more mature plants,” explains Dr Andrew Taylor. “We’re seeing increasingly severe cases where entire onion fields are lost.”

Higher than normal average temperatures have led to increased UK losses this year. Andrew warns that the problem may get worse: “FBR likes warm, wet conditions, and based on current climate change predications, the UK is becoming more conducive to this disease.”

There has been little research investment into ways to prevent and reduce the damage caused by FBR. However, since 2009 the Defra-funded research project 'VeGIN' (Vegetable Genetic Improvement Network) at the Warwick Crop Centre has helped to increase our understanding of the disease. 

Dr John Clarkson: “Fusarium oxysporum produces long-lived spores that can survive for many years. This explains why attempts to control the disease through long rotations, soil sterilisation and drenches with fungicides have had limited success.”

To limit environmental impact, and taking into account legislation restricting pesticide use in some countries, Andrew and John are focussing on developing disease-resistant varieties of onion.

“Identifying and developing disease-resistant onions is much more of an environmentally- friendly and sustainable approach,” says John.

In the VeGIN project, onion lines were exposed to a highly virulent strain of Fusarium and screened for resistance. This allowed identification of a range of resistance responses in onion lines ranging from ‘highly susceptible’ through to ‘moderately resistant’ and ‘highly resistant’ lines. By the end of 2012, several highly resistant onion lines had been verified. 

As part of the Horticulture and Potato Initiative (HAPI), a new BBSRC-funded project starts in April 2014 to develop this research further.

“One of the main aims of the work will be to use next generation DNA sequencing to identify the genetic basis for Fusarium resistance so that DNA-based markers can be developed to accelerate breeding of new resistant onion varieties.

“This should provide us with the information, tools and resources to understand the genetics that control resistance [and] will allow resistance genes to be tracked throughout the breeding process and new onion lines to be rapidly genetically screened for resistance.”

Another aim is to identify the genes that enable particular strains of F. oxysporum to specifically attack onions. This could help scientists to understand how different fungal strains attack different crops, and may aid in the development of diagnostic kits.

Alongside developing disease resistant onions, the team also needs to develop varieties of onion that meet agricultural and consumer needs too, as John explains: “The new varieties need to have characteristics that are essential for commercial production such as high yield, uniform bulb size, and ability to store well.

“Although this is a long term goal, we have made significant progress towards finding a solution to a globally important onion disease which threatens current and future food security.”

This story has been adapted from the news item on the University of Warwick website here: http://www2.warwick.ac.uk/knowledge/science/finding-a-solution-to-fusarium-basal-rot-the-onion-that-threatens-the-staple-vegetable#.Une-o5RHDpc

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