THE GREAT FAMINE: Gone, But Not Forgotten
By Sean Henahan, Access Excellence
One-hundred and fifty years ago a fungus called
Phytophthora infestans began a destructive process that would
change the course of Irish and, indirectly, world history. The
country is now commemorating the 150th anniversary of the potato
famine that would lead to the deaths of millions of citizens and
the emigration of many millions more.
A hundred and fifty years ago in September, 1845, the Dublin
Evening Post reported a "disease in the potato crop". This turned
out to be potato blight which destroyed 40% of the crop that year
and almost 100% the following year. The ensuing devastation was
known as "The Great Hunger" and resulted in widespread starvation
and mass emigration to Britain and the Americas. As a result the
population declined from 8,295,000 to less than six million in a
few short years.
Towards the end of the 18th century and well into the 19th
there was a rapid rise in the Irish population. More and more
land was used for potato growing to the neglect of other crops.
Some of the older, better quality potatoes were abandoned in
favor of the high yielding but poor quality "Lumper". By 1800,
90% of the population were wholly dependent on the potato and in
large parts of the country many depended on a single variety,
In 1845 a fungal disease, called late blight, appeared in
the Irish potato crop with devastating results. The disease,
called late blight, manifests itself in any part of the plant.
Discoloration of the leaves accompanied by downy mildew is
sometimes the first sign. The tubers may also be infected in the
field or in storage, with discoloration of the skin, with a
reddish brown dry rot extending
into the tuber. Later a slimy, foul smelling rot may destroy the
It is now known that the blight is caused by the fungus
Phytophthora infestans an Oomycete (class) which belongs to the
family Pythiaceae. This species is characterized by coenocytic
mycelium and the production of biflagellate, motile zoospores.
The fungus is heterothallic and can reproduce sexually in the
presence of an opposite mating type. Sexual reproduction follows
fertilization of an oogonium by an antheridium resulting in the
production of an oospore. Overwintering can be in the form of
resting mycelium (most usual) or oospores. After germination both
will result in the production of sporangia which can germinate
directly by means of a germ tube or indirectly by means of the
motile zoospores. Germination is followed by encystment and
Penetration of the leaf surface is by means of an infection
peg followed by intercellular invasion with penetration of the
cells by means of an haustorium. Invasion of he leaf is rapid,
eventually resulting in necrosis and death of the leaf tissue.
Under favorable conditions, the sporangiophores emerge through
the stomata with a fresh crop of sporangia within 4 to 5 days of
the initial infection. This multicycle, airborne pathogen can
therefore spread rapidly within crops and from one crop to
About 40% of the potato crop was lost to the blight in
1845,and the entire crop was lost by early August, 1846. The
loss of that year's crop had its worst effects in the early part
"Black '47", the year when mass emigration started,. Apart from
starvation, the lack of food led to other diseases such as
scurvy, dysentery, typhus and cholera. Although the 1847 crop was
unaffected by blight, famine conditions intensified because there
was a shortage of seed potatoes and not enough potatoes had been
In 1845 the population of Ireland was estimated at
8,295,000. When in 1851 the famine was officially over, the
population had been reduced by some two and a half million. One
and a half
million people had died of starvation and disease and a further
million had emigrated.
Phytohphthora infestans also affected potato crops in the
northeastern United States and Southern Canada as well as much of
western Europe in addition to Ireland in 1845, but the effects
were nowhere near as devastating as in Ireland because in those
places the diet was much more diversified and the people were not
so dependent on the potato.
In 1882, Millardet, a French botanist, noticed that grapes
in a vineyard which had been sprayed with a mixture of copper
sulfate and hydrated lime (in order to prevent theft) had
free from attacks of downy mildew. Millardet went on to
demonstrate the effectiveness of this "Bordeaux Mixture" in
preventing potato blight. By the beginning of the twentieth
century, spraying of potatoes with this fungicide was in general
use in Ireland and remained so until the introduction of organic
fungicides in 1934, and more recently, the newer systemics.
Potato breeders are attempting to develop "field resistance"
or durable resistance to the fungus. The Lumper, the potato of
the famine times is no longer grown. About 25 varieties of
potatoes are grown commercially in Ireland today. The main
variety grown is Kerr's Pink which has low resistance to blight.
Three other popular varieties, Record, Golden Wonder and Rooster
have very good resistance to tuber blight and moderate resistance
to foliage blight. Another popular variety, Cara, has excellent
tuber and foliage resistance. The gene R2 has been found to delay
the onset of an epidemic by 10 to 14 days and attempts to
incorporate this gene into varieties with a high level of durable
resistance are underway.
A complex strategy of blight control has been developed
involving protectant, systemic and translaminar fungicides, at
times combined with adjuvants to enhance their effectiveness.
This strategy is designed to control the blight and avoid the
problem of fungus resistance.
Although it happened 150 years ago, the Irish have not
forgotten "The Great Hunger". Because of the influence of weather
on the development and spread of late blight, the Irish
Meteorological Service continues to broadcast warnings of weather
favoring the spread of
potato blight. Moreover, the Irish people have gained a
reputation for contributing personnel and resources in areas of
the world currently facing famine, well out of proportion to the
size and economy of their small island.
Anyone planning on visiting Ireland may want to visit the
recently opened Famine Museum at Strokestown House, Co.
Related information at other Web sites
Irish Potato Famine Web Page
More Irish Famine Links