Ever since we domesticated the first plants for food production, humanity has been dragged into the age-old arm’s race that exists between our crops and their pathogens...

The impact of one single crop pathogen on human society can be of a dreadful scale, especially when our crops are not naturally protected against them. The best example to illustrate this is the potato epidemic that caused the Great Irish famine in the mid-19th century. The culprit, an American microbe named Phytophthora infestans, crossed the Atlantic by ship, reached the European continent and wiped out entire potato harvests over various consecutive years. The impact was most devastating in Ireland, where people were highly dependent on one single variety of potato that did not bear strong natural resistance against the pathogen. About a million people died of starvation and another million or more were forced to leave the country. The famine reduced Ireland’s population by 25%, and the country has still not yet recovered to its original population size, even today.

It would, nonetheless, be very wrong to think that the threat of starvation due to crop pathogens is a problem of the past. According to the Food and Agriculture Organization (FAO) of the UN, at least 20% of global food production is lost due to plant disease and over 800 million people are chronically undernourished worldwide. In addition, the globalisation of trade since the Second World War combined with a lack of thorough disease control has allowed the spread of local pathogens to every corner of the world. And now, with the threat of climate change coming nearer and nearer, the future of agriculture in the face of disease becomes more uncertain. Simply eradicating pathogens is, however, practically impossible and ecologically irresponsible. What would provide us with more sustainable ways of combating crop disease and hunger, and equip us better for the changes to come, is a thorough understanding on how plant pathogens spread, colonise and adapt to their hosts in the first place, so that our agricultural systems can always be a step ahead of disease. For that, the history of a crop pathogen and its spread is a great starting point.

Read on: https://www.thenakedscientists.com/articles/science-features/what-herbaria-tell-us-about-crop-pathogens