Plant Health Week – day 5

Humble spuds have a very interesting history. Originating in South America, the earliest finds date from about 2500 BCE. It subsequently became a staple food for indigenous people in Andes region, the main energy source for those living in the Inca Empire. It arrived in Europe as early as mid-16th century but the acceptance as the food was initially low. It took the efforts of the French and German governments and landowners in the second half of the 18th century for the potato to become a staple crop in northern Europe. Perhaps the famines of 1770s helped as well. The crop was resistant to spoilage, easy for cultivation even on small fields and gardens, and a good source of calories and some vitamins and minerals. It appears to have arrived in the US via Ireland. Today, potatoes are grown across the globe, but with the highest concentration in Europe, India, China and the US.

Frederick the Great encouraging potato planting. By Robert Müller –, Public Domain,

King of Prussia, Frederick the Great, is sometimes called der Kartoffelkönig – potato king – as he was instrumental in introducing the crop into Prussia and Eastern Europe. By 1840s, potatoes accounted for 11% of Prussian and 14% of Belgian arable land, but it was Ireland that adopted the plant as the main source of food (32% of arable land). A whole Irish (or British, or German, or Polish) family could survive by growing potatoes on a single acre of land. It could also be grown in city gardens, supplementing the diet of Industrial Revolution workers.

Symptom of late blight on the underside of a potato leaf
Phytophthora infestans symptoms. By Howard F. Schwartz, Colorado State University, United States –, CC BY 3.0,

The rapid growth of potato cultivation was not, however, associated with good biosecurity practices. The American and European crops were dominated by a single variety (called Lumper; it was not resistant to blight but with a high yield), so it was a disaster in waiting. Indeed, in the early 1800s, potato blight (Phytophthora infestans) started spreading in Central and North America and it arrived in Europe in 1840s.

The map of approximate potato blight spread in 1845.Source unknown.

Starting in northern France and Belgium in June 1845, it rapidly spread throughout Europe, reaching Ireland in September-October. A catastrophic failure in the crop that supported the Irish combined with the failure to help the starving population led to a million deaths and possibly two million leaving the country.

Population of Ireland. Source unknown.

Scotland, and particularly Scottish Highlands, were affected as well leading to migration. US and Canadian people celebrate their Irish and Scottish ancestry, perhaps not realising that their origins are due to a plant pathogen.

However, it was not only the populations of Ireland and Scotland who were affected, as the famine spread throughout Europe resulting in losses as high as 80% in Belgium and 50% in Denmark and parts of German Empire. As other crops (wheat, rye, oats) also failed in 1845 and 1846, there was a general shortage of food. Food prices were rising and the demand for goods produced in newly industrialising nations fell. Unemployment led to general dissatisfaction with the governments. The Spring of Nations, the Revolutions of 1848 followed suit.

Philippoteaux - Lamartine in front of the Town Hall of Paris rejects the red flag.jpg
By Henri Félix Emmanuel Philippoteaux, Public Domain,

While it is perhaps a stretch of the imagination to say that the 1848 revolutions were the result of the potato famine, the loss of food security – caused by Phytophthora infestans – certainly contributed to people’s dissatisfaction with the governments.

The potato blight is still a huge problem, even though we now have ways to treat it. Some pesticides are based on copper. Because of the shortages of the metal during World War 1 (used to produce shells and wires), a major outbreak devastated potato crop in Germany, leading to mass starvation. Using resistant varieties is one way to battle it, as is using good quality seed potatoes (Scottish ones are best in the world!).

Visit The Grave Of Frederick The Great - Berlin Experiences
Frederick the Great’s grave.

And, people still remember the Prussian King, Frederick the Great and his contribution to potato cultivation by placing tubers on his grave (thanks to Agnieszka for this link!).

[The previous version associated the 1848 Revolution with Les Miserables, but of course the events in Victor Hugo’s book are the 1832 uprising, not the 1848 revolution; apologies for the mix-up! In fact, the 1832 uprising was also associated with harvest failures and cholera outbreaks – epidemics are everywhere!]

Plant Health Week – day 4

Back in 2009 I was with my family in Poland and we were doing some hill walking in Beskidy, a beautiful mountain range in South Poland. Hills in that range are usually well covered by forests, both mixed and single species – mostly spruce. This is what I was used to at least.

Spruce forest in Beskidy, Poland, 2009.

However, in places, the mature spruce forest was giving way to patches of a rather sad looking dead trees. When the landscape opened even more, we were walking through miles and miles of a apocalyptic-looking dead tree forests; the result of a combined drought and bark beetle onslaught.

Spruce forest in Beskidy, Poland, 2009

Ips typographus, known as an eight-toothed spruce bark beetle or the European spruce bark beetle, is a serious and destructive pest of trees. It usually attacks weakened trees, so its outbreaks often follows dry periods when spruce – with its rather shallow roots – becomes particularly stressed. But, if summers are long and warm, the beetle can fit several generations (from eggs through larvae to adults) into the year. As each generation represents an exponential increase compared to the previous one, a huge outbreak can follow. The resulting density of beetles can overcome the resistance even of healthy trees, resulting in a massive outbreak which devastated forest in southern Poland and nearby Czech Republic and Slovakia.

Map of South Poland showing the extend of deforestration – colours denote year of forest loss, with purple to light blue corresponding to 2001-2009 and green to red corresponding to 2010-2018.

This pattern is now being repeated again and again in different locations and with different trees and pests. As the climate becomes warmer, with less snow and higher temperature in winters forest insects like Ips typographus are finding it easier to survive. Less snow in winter and hotter summers also means drought which stresses trees. This combination is likely to lead to more and more disappearing forests – at least forests as we know them.

Don’s risk it!

What can we do? Ips typographus is a native in continental Europe, but not present in the UK. We can try to make sure it is not brought into the UK by accident, and if it arrives – as it happened in Kent in 2018 – to eradicate it as quickly as possible.

Beskidy forest, 2009

We can also replant the forests with other trees, recognising that perhaps the forests we are used to might need to look differently in 20, 50 or hundred years. This requires a lot of planning of how to adapt the forests to the climate change and make them useful as well as beautiful.

Me in Białowieża Forest in northern Poland, 2019. Białowieża is a unique old forest which has recently been devastated by Ips typographus.

Plant Health Week – day 3

Having written about two very large and very important plant diseases, I want today to focus on a much less known fungal pathogen, Rhizoctonia solani.

Department of Plant Sciences

There is a personal aspect to it. In 1993 I joined the Department of Plant Sciences at the University of Cambridge as a post-doctoral researcher. I already had been working on human disease modelling, but this was the first time I encountered plant pathogens. Colleagues who were biologists and mycologists introduced me to a wonderful world of soil-borne fungi. I have been fascinated with the fungi ever since.

Rhizoctonia solani damping off on radish seedlings.

Rhizoctonia is a group of fungi causing various symptoms in plants, including sheath blight (the second-most devastating disease of rice after rice blast) and damping-off which affects seedlings. In the field, it can form densely infected patches causing large yield losses.

Rhizoctonia experiments

As a modeller, I was not allowed to do experiments (in case I do something stupid which will spoil the work), but I enjoyed seeing the experiments set up. We grew Rhizoctonia solani in trays filled with sand in which seedlings of brassicas (radish, cauliflower) were planted.

Rhizoctonia experiments

Another fungus, Trichoderma viride was introduced on poppy seeds, in an attempt to control the disease. A poppy seed had to be placed in an exact position and if dropped by mistake, they would ruin the experiment. It was amazing that the poppy seeds could not really be distinguished from grains of sand which made placing them tricky – but Rhizoctonia knew exactly where they were. A race between Rhizoctonia and Trichoderma ensued to see which one will get to “food” earlier.

Field experiments

We also did field experiments and I really enjoyed going out, meeting farmers and getting my boots dirty. Talking to people who actually grow the plants – propagators, farmers and farm managers – made me realise that mathematical and statistical modelling of plant pests and diseases must be connected to economics and behavioural sciences – a line of research that I have been pursuing since.