David Moore's World of Fungi: where mycology starts

The word ‘murrain’ is not in common usage these days; in fact most dictionaries describe it as being obsolete. It’s the word that was used at the time and the word stayed with the story as it passed into history.

A ‘murrain’ is a great pestilence, a disease so widespread that it becomes a plague. This story deals with just such a terrible disease of the potato crop. Before developing the story, though, it’s essential to put it into historical scientific context.

The events mostly took place in 1845 and 1846. This was around twenty-five years before the great French microbiologist Louis Pasteur proposed his theory that diseases (of humans and animals) were caused by ‘microbes’ or ‘germs’. The mid-nineteenth century had little concept of disease beyond its being an affliction. An individual’s beliefs and prejudices might then determine their convictions about the cause of the affliction; which they might see as a judgement from God, maybe, or the work of the Devil, or maybe that witch down the lane, or even “…him next door, you know, the one with the evil eye.”

Nobody at that time would immediately associate dying plants with an infection. The first report of what was to develop into such a calamity can be found in a letter from Dr Bell Salter in the Isle of Wight to The Gardeners’ Chronicle and Agricultural Gazette. In the edition dated August 16th, 1845 Dr Salter reported the arrival in England of a new malady of the potato. Matters progressed so rapidly that the distinguished editor of that journal, Dr John Lindley published in his editorial the next week, August 23rd, that:

‘A fatal malady has broken out amongst the potato crop. On all sides we hear of the destruction. In Belgium the fields are said to have been completely desolated. There is hardly a sound sample in Covent Garden Market.’

The potato crop had been affected before, just like other crops. Damaged by too much rain in wet seasons or by too little rain when there was a drought. Sometimes the tubers were scabby and inferior quality, sometimes the leaves curled up and the crop was reduced. But nothing as destructive as this new murrain had been experienced before. Growing plants looked like they had been badly affected by frost (remember this was in August; the summer season). Lindley’s editorial told the story:

‘The first obvious sign is the appearance on the edge of the leaf of a black spot which gradually spreads; the gangrene then attacks the haulms (stems), and in a few days the latter are decayed, emitting a peculiar and rather offensive odor. When the attack is severe the tubers also decay.’

Lindley recognized that if this ‘gangrene’ continued to spread, an important part of the country’s food supplies for the coming winter would be lost. He offered little hope for treatment, though, saying:

‘As to cure for this distemper there is none. One of our correspondents is already angry with us for not telling the public how to stop it; he ought to consider that Man has no power to arrest the dispensations of Providence. We are visited by a great calamity which we must bear.’

But who would bear the greatest calamity? As August became September reports of the spread of the murrain came from Poland, Germany, Belgium, France, and from all over England. Lindley’s fears were not exaggerated. Every strain of potato in cultivation was attacked. When they were dug from the field the potatoes were blotched with the dark patches of rotting flesh that were symptomatic of the disease. Patches coloured like bruised and battered human flesh. Patches that smelled of pestilence.

And they spread. This was not something which ended when the crop was lifted. Leave potatoes on the floor of a barn for a few days and they became worse than when they were lifted. This was the unique character of the potato murrain. It spread amongst potatoes in the ground and also amongst those in store. The crop you might have thought safely harvested and stored could rot away in a few days; every tuber, no matter how slightly affected, would be lost.

There is a record of a shipment of potatoes sent, routinely, by ship from the East coast seaport of Kingston-upon-Hull to be marketed in Belgium. Two thousand tons of potatoes left Hull in sound, palatable condition, but the entire cargo was rotten before the ship reached its destination just a few days later.

Then, on September 13th Lindley made the most dramatic announcement in The Gardeners’ Chronicle:

‘We stop the Press, with very great regret, to announce that the Potato Murrain has unequivocally declared itself in Ireland. The crops about Dublin are suddenly perishing ... where will Ireland be, in the event of a universal potato rot?’

The potato murrain affected the whole of Europe, but right from the very start, it was clear that the Irish peasants would suffer most. Loss of the potato crop in England would bring distress, of course, but the poorest labourers in England lived on oat gruel and bread as well as potatoes. The cereal crops were intact and so a major proportion of their normal diet was still available.

In Ireland, on the other hand, the poorest members of the population lived almost exclusively on potatoes. On average four to seven kilograms of potatoes per day, per person, day in, day out, for ten months of the year. That’s just over 5 tons per family per year. The only break in the cycle occurred in July and August, the gap between the old and the new potato crops, when they had to subsist on wheat meal and anything else they could find.

The population of Ireland had grown from four million in 1800 to over eight million in 1845, largely because of the ability of the potato plant to provide large crops of easily-stored tubers from small holdings on even relatively poor land. One acre of average land could produce six tons of potatoes each year; enough for the average family. The tubers were easy to store over winter, so the potato had brought reliability of food supply to the poorest peasant farmers.

It was clear to everybody that if the Potato Murrain spread through the small-holdings of Ireland there would be millions of men, women, and children, who would starve to death. And spread it did.

The crops of 1845 and 1846 were lost. In 1847 there was good weather and though there was a very much reduced acreage under potatoes in Ireland, the murrain was localized and relatively unimportant. With brilliant sunshine from July to September that year over the whole of Europe, harvests of grain and potatoes were good. The two worst years of famine were past but the misery went on in the shattered Irish countryside.

Two years of famine were devastating. In the years from 1845 to 1860, one million people died in Ireland as a direct consequence of the famine, and over two million emigrated. Those that survived changed the world.

Many headed for North America and the ‘Paddies’ became the labour force that built the foundation of the USA. They brought the Catholic Church to a position of prominence in a nation founded by Protestants. And now, 20% of the US population claim Irish ancestry.

They changed Ireland, too, creating a pattern of Ireland being an exporter of people. There’s an estimate that in the hundred years between 1830 and 1930 50% of those born in Ireland left the country to make their permanent home elsewhere. Ireland, now becoming a European ‘Tiger economy’ within the European Union, reported only in 1996 its first net gain in population since the famine.

The social upheaval caused by the Irish potato famine changed the demographic and political structure of the whole world and made an enormous contribution to the structure of the socio-economic civilization we enjoy today. It was caused by the potato murrain, so just exactly what was it? The main intellects of the day were unable to come up with a cause, much less a cure. There was an official Commission of Enquiry which recommended some perfectly sensible methods of storage for sound potatoes. But the crop then being harvested was not sound and the tubers continued to rot in the stores. It’s easy to be dismissive in retrospect but at the time it’s difficult to see what other advice the government’s scientists could offer. Probably, for the time, the best the Government of the day could do is what it did.

Prime Minister Peel requested a survey of the state of the Irish potato crop. In response to this, on 16 September 1845 the Inspector General of Constabulary, a Mr D. McGregor, issued a strictly confidential circular from the Constabulary Office in Dublin Castle which started:

‘Information having reached the Government that the POTATO CROP of the present year has totally failed, from disease, in many districts of this Country, County and Sub-Inspectors of Constabulary are hereby directed to make full and immediate inquiries respecting the state of this Crop in their several Districts, and to report the result of such inquiries without loss of time ... These inquiries are not only to be regarded as confidential but they are to be so conducted as to prevent speculation on the possible motives for seeking the information required.’

Over two hundred of these disease reports had been received by the end of September. The extent of the disease was quite clear. The impact was also evident. Sir William Wilde wrote in the Dublin University Magazine of 1854 that:

‘The late Bishop Brinkley, one of the most profound thinkers we have ever had in Ireland, who predicted the loss of the potato many years ago, and calculated mathematically the extent of ruin which was likely to follow, declared to his relative, the late Dr. Graves, that he was unable to sleep for an entire night, owing to the effect that it had upon him.’

From conscientious gathering of information the government knew that about two million people were dependent entirely on the potato for food in Ireland and £8 million were put into a relief effort in eighteen months between 1845 and 1847. That is about £1 sterling for every soul in Ireland at a time when the agricultural labourer earned about £2 per year. A colossal amount for the day, though the tragedy was so great that even this relief effort was overwhelmed.

As to the real cause, well, there were some hints. The peculiar changes of weather which had occurred during the summer of 1845 must have had much to do with the outbreak and spread of the potato murrain. The early part of the season that year was good; good for planting, good for early growth, so the crops looked really promising right up to July. In July the weather was hot and dry. The temperatures up to four degrees above the average for previous years. Somebody called Mr F. J. Graham recorded all this in an essay on the history of the murrain, which won a prize and was eventually published in the Journal of the Royal Agricultural Society. He went on:

‘It then suddenly changed to the most extraordinary contrast that I ever witnessed in this fickle climate, the atmosphere being for upwards of three weeks one of continued gloom, the sun scarcely ever visible during the time, with a succession of most chilling rains and some fog, and for six weeks the temperature was from 1.5 degrees to 7 degrees below the average for the past nineteen years.’

Dr Lindley theorized about the cause of the murrain, though his explanation was wrong. Lindley argued that it was the result of this cold and wet July weather causing the potato plants to become overladen with water. The man who got the explanation right, at the time, was the Reverend Miles Joseph Berkeley who was, in Lindley’s words,

‘a gentleman eminent above all other naturalists of the United Kingdom in his knowledge of the habits of fungi’.

Berkeley associated the murrain with growth of a kind of mould (= hyphal growth) in the affected tissues. He saw the damaged foliage himself in his parish, near King’s Cliffe in Northamptonshire, and put forward the revolutionary theory that the mould was the cause and not the consequence of the potato murrain. That the murrain, in other words, was a disease. Lindley argued that Berkeley was taking his interest in fungi too far, and that any mould that might be present was one of the

‘... myriads of creatures whose life could only be maintained by the decomposing bodies of their neighbours ...’

The way in which moulds and mildews appeared, almost overnight, and how they reproduced was a great mystery at the time. Felice Fontana had examined rust on wheat under a microscope in 1767, recognizing it as a minute vegetable with bodies resembling seeds. Indeed, in 1807 in France, Bénédict Prévost had actually seen the spores of the bunt fungus on wheat germinating like seeds in water. Nevertheless, it was still commonly believed that small fungi could be produced in decaying matter by spontaneous generation.

Robert Hooke published his Micrographia in 1667. He was the first person ever to use a compound microscope to describe the appearance of fungus growth. He examined a blue mould on some old leather and some rose leaves which had yellow spots on them. His opinion was that:

‘the blue and white and several kinds of hairy spots, which are observable on different kinds of putrify’d bodies are all of them nothing else but several kinds of small and variously-figured mushrooms, which from convenient materials in those putrefying bodies, are by the concurrent heat of the air, excited to a certain kind of vegetation’.

The belief of the day, therefore, was that putrefaction caused the appearance of the lesser organisms. The Rev. M. J. Berkeley was going against this core belief by making his suggestion. But he was in frequent correspondence with other naturalists in Europe so from their observations he was able to confirm that the same mould fungus was associated with this potato disease across the Channel. The same mould was on the diseased potatoes themselves. Though Berkeley had never seen this particular species of mould before, it resembled one he had seen growing on onions and shallots. It also appeared to be related to the fungus which was associated with a very serious disease of silkworms in Europe. The potato murrain, the Rev. M. J. Berkeley insisted, was due to the growth of this particular fungus, and no other, as a parasite on the potato plants.

Berkeley called it a species of Botrytis infestans; today we call it Phytophthora infestans, the causal organism of the Late Blight of Potato. The cool, wet and very humid weather at the end of July favoured the spread of this moisture-loving fungus and the disease became an epidemic.

There is great scientific significance in Berkeley’s ideas as to the most probable cause of the potato murrain. His was a new conception of the nature of disease. By advancing the hypothesis that a living parasitic organism on the potato foliage was the cause and not the consequence of the potato murrain the Rev. Berkeley was doing no less than anticipating the germ theory of Pasteur by almost twenty-five years.

Of course, Pasteur proved it, Berkeley only suggested it. But it’s a measure of the intellect of the cleric who was at work in King’s Cliffe in Northamptonshire late in the summer of 1845. Sadly, despite all the varied intellects which were devoted to the potato murrain no cure or treatment emerged.

A sad postscript to this story is that one person of the day did have an effective way of saving the potato crop. It was widely known that the murrain started on the foliage of the potato plant and then made its way to the tubers. A Dr Morren in Belgium pointed out that if the upper parts of affected plants were removed and destroyed, the tubers remained healthy. And he did this within two weeks of the first appearance of the murrain in 1845. If Morren’s measure had been adopted, much of the potato crop could have been saved in the famine years.

Hindsight is a wonderful thing.