East Anglia is a major producer of sugar beet (Beta vulgaris) in the UK. Before I moved from London to East Anglia to go to university I don’t think I had heard of sugar beet and I certainly didn’t know that a large amount of the sugar in my diet and in my cake baking came from it (I thought it all came from sugar cane grown in tropical regions). Being a plant scientist and living in a sugar beet growing area has given me greater exposure to this interesting plant so when I heard some worrying news about it in the media I decided to highlight it as this week’s organism.
In East Anglia, farmers have been reporting the failure of sugar beet seedlings to germinate and the shoots to emerge above ground (1). In some areas more than 50% of the crop has been affected. At the moment it is not clear what is causing this problem, but it is possible that this year’s cold spring may have had an impact. Several varieties have been affected so it is not just a case of a single bad seed batch. Bizarrely, neighbouring fields sown with the same seeds can be affected differently with one field having normal levels of germination and emergence and the next having only 50% of the crop growing. Many farmers are now expecting substantially reduced yields and therefore loss of earnings for this year’s crop.
This mystery illness is worrying because the sugar beet industry is rather large with sugar beet accounting for 20% of the world’s total sugar produced in 2009 (3), second to sugar cane. Unlike sugar cane, which grows in tropical regions, sugar beet grows in temperate climates with the top producers of sugar beet being Russia, France, USA and Germany. Producing sugar from sugar beet became an increasingly important industry in Europe during the 19th century but didn’t catch on in the UK until the 1920’s, after shortages of sugar cane during the First World War drove interest in home-grown sugar production. Today, UK-grown sugar beet meets around 50% of UK sugar demand (2) with the rest coming from sugar cane-derived imports.
In the UK the annual sugar beet “campaign”, which is when the crop is harvested, delivered to the factories and processed into sugar, starts in September and lasts about 5 months. Fortunately even once the crop has been harvested the roots do not degrade very quickly so the crop can be stored (often in large piles on the edges of fields) before processing. However, if the crop freezes during the cold winter months it needs to be processed before it thaws in the spring as the thawing process results in sugar loss and affects the structure of the root making it more difficult to process. Once it arrives at the factory the beet is washed, chopped and passed through a diffuser that extracts the sugar from the beet by boiling it. The resulting raw sugar juice is then processed to remove impurities and then the purified sugar is crystallised.
The quality and yield of sugar beet crops can be affected by a number of factors including: climate, pests, diseases and competition from weeds. One disease that causes large yield losses is rhizomania, where instead of producing a large single tap root the plant develops many small roots, resulting in reduced root mass and lower sugar content (click here for a picture of healthy vs rhizomania roots). The disease is caused by Beet Necrotic Yellow Vein Virus (BNYVV) and is transmitted by a soilbourne fungus called Polymyxa betae that infects the roots of the sugar beet (4, 5). Yield losses due to rhizomania are often as high as 50-60% especially if the crop is infected early in the growing season (5). The BNYVV virus survives in spores of P. betae and there are not currently any effective forms of chemical control so once soil is infected it generally remains so.
Control of rhizomania currently relies on the use of resistant varieties developed by conventional breeding. Most of these varieties carry a single resistance gene Rz1. Unfortunately using a single form of resistance in the sugar beet puts selective pressure on the virus to evolve resistance to that trait. Variants of the BNYVV virus that can overcome the Rz1 resistance in the sugar beet have already been identified in some areas (5). To avoid the complete breakdown of resistance to the virus in the sugar beet other forms of resistance need to be developed, with the development of sugar beet varieties containing several resistance genes being preferable. More robust resistance could be achieved by breeding varieties that have resistance to both the virus and infection by the P.betae fungus.
In the UK most sugar beet research is carried out by or in association with The British Beet Research Organisation (BBRO). The BBRO are already investigating the mystery illness that has struck down this year’s sugar beet crop but this will not change the fact that 2013 looks set to be a difficult year both the UK sugar beet producers and the processor British Sugar.
Something to think about next time you put sugar in your tea or bake a cake!
British Beet Research Organisation http://www.bbro.co.uk/home
British Sugar http://www.britishsugar.co.uk/uk-beet-history.aspx
(1) BBC news http://www.bbc.co.uk/news/uk-england-22536822
(3) Agribusiness Handbook: Sugar beet white sugar, Food and Agriculture Organization, United Nations (2009)
(5) McGrann et al (2009) Progress towards the understanding and control of sugar beet rhizomania disease. Mol Plant Pathol.