Here in the Northeast, we’re experiencing the coldest, wettest and darkest summer in recent memory. The tomato crops of many farm and home gardens have been decimated by a disease that thrives on just this sort of weather. The disease is late blight, caused by a water mold named Phytophthora infestans. The severity and incidence of the disease is the worst that anyone can remember.
Several important and timely lessons can be taken from the destruction of these farm and home garden tomato crops. But first, let’s revisit a time long ago when almost the exact same conditions as we have experienced for the last 5 months—unseasonably cool, wet, and overcast days—continued nonstop for 5 years and led to the Great Irish Potato Famine of the 1840s.
Records show that northern Europe was battered by persistently gloomy springs, summers and autumns interrupted only by the typical dark winters. This weather—of which we’ve received a 5-month dose—so favored late blight that all but a fraction of Ireland’s potato crop was devastated for several consecutive years. It is hardly known that the rest of Europe and the United States suffered from potato losses only slightly less devastating than those that occurred in Ireland. The tragic difference was that these other parts of Europe and the United States had a more diverse food crop base than did Ireland, where over a million people starved and from which several million emigrated over the subsequent decade.
Even lesser known is the surprising fact that, contrary to conventional wisdom, in the 1840s there were nearly two dozen distinct potato cultivars grown throughout Ireland and over fifty in the rest of Europe. Far from the popular image of a “monoculture”, potatoes grown in Ireland included a diverse group of white, yellow, pink, brown and red skinned varieties. These had been collected both in the wild and from native markets in South America and deposited in the botanical gardens of Europe over 300 years before the famine. While it is certainly true that many of these various cultivars existed within a “type” of all-purpose boiling and mashing potato, it’s also true that, out of this quite diverse gene pool, post-famine “survivors” appeared. These became the ancestors of new and resistant potato cultivars grown to this very day.*
Therefore, the first lesson to be learned from the near collapse of so many fields of tomatoes on farms and in home gardens dotted across the northeastern United States, is that no normal diversity of cultivars or genetic variation can resist an aggressive, virulent strain of the late blight organism under conditions that nurture its explosive growth and dispersal.
However, there is a second lesson that is of—literally—great value. Modern hybrid tomatoes—carefully and deliberately developed over many years—possess sufficient vigor to withstand all sorts of diseases, including a particularly destructive and widespread attack of late blight.
This is vividly demonstrated in the high survival rates of hybrid tomatoes throughout the hardest hit growing regions. In our trial gardens at Fordhook Farm, we see rows of old-fashioned heirlooms and open-pollinated market varieties of tomatoes lying in heaps of wilted foliage and diseased fruit, and—just a few feet away—rows of healthy hybrid plants loaded with heavy, flawless fruit.
As the name implies, late blight generally occurs later in the season. It has never occurred this early nor been so widespread in the United States; last year there were only a few reported incidences of the disease. The same varieties of tomato have been grown in the Northeast for years, and the various stains of the disease-causing organism have likewise been present for years. However, our recent, freakishly unseasonable weather has been ideal for the growth of the organism and the spread of the disease.
If the spring and summer of 2009 is followed in succession by similar seasons in 2010, 2011, 2012 and 2013, we could face a complete extinction of many—not all—of the old-fashioned heirlooms and open-pollinated tomato varieties that folks in the Northeast have come to enjoy since those varieties were reintroduced in the early 1980s. However, just as there were survivors among the potato varieties that succumbed during the years of the great famine and which gave rise to the modern, resistant potatoes of today, so the hybrid tomatoes of the 20th century as well as those of the early 21st century will be the saving grace of tomato lovers everywhere. We might even discover utterly new sources of resistance, although that will probably come from wild, weedy relatives of tomato and potato. It’s the silver lining of, quite literally, a very dark storm cloud.
Media stories about the monolithic food industry, Big Agriculture, “bioengineering”, and “industrial farms” ill inform us of the virtues of modern agriculture and obscure the role of plant breeding as a science and discipline. Plant breeders who work in productive crops such as wheat, corn, rice, potatoes, and the wide range of vegetables and fruits upon which the world depends, struggle toward their various goals with many positive purposes in mind. One of the most important of these is disease resistance.
Plant breeding is ancient. In its essence, it was probably practiced before agriculture was widespread. Early nomadic people may have saved seed that was larger or that was easily separated from unwanted parts, carried it with them, and planted it far from its source. In this way, they honed plant characteristics that were useful to them.
Plant breeding has its formal roots in the work of the humble Austrian monk, Gregor Mendel, who with the common pea first demonstrated predictable patterns in the transmission of genetic traits. Since Mendel, plant breeding has progressed to the point that scientists are able to breed food crops that can thrive in salty water and deep shade and withstand a host of pests while, at the same time, yield abundant and delicious produce. It has been due to the skill of the plant breeder that plants have been selected and hybridized so that they require less water, less space, less fertilizer, and less protective chemicals. This is the height of human discernment.
Society should cherish the human ability to select different traits from various plant populations and mix them together, just as Nature would under ideal circumstances. Call plant breeders the “nuclear physicists” of the biology world.
* To elaborate, let’s take Ireland in the 1840s. In a nation smaller than the state of Maine, the Irish had raised potatoes for at least 125 years. Within the two-dozen distinct or unique varieties, there was a wide variation due to the separate and diverse genetic background of each cultivar. They differed in tuber size, tuber shape, size of yield, time of yield, quality of tuber (wet or dry), color of skin, color of flesh, thickness of skin, ability to tolerate bad soils (hard or low in nutrients, etc.) and ability to remain viable in long periods of storage.
More interesting to my point is that they differed also in resistance to heat, to cold and to frost. Plus, they varied in resistance to a virus called “Leaf Curl”, as well as to a tendency of tubers to develop warts, and—most important—to fungi and molds. This last genetic variability proved decisive in providing the post-famine Irish with new varieties—based partly on the surviving potatoes—that would replace those that lacked the strength to fight off late blight, a phenomenally destructive plant disease caused by a water mold or more technically an Oomycete.
So, an interesting question might be: Do today’s potato farmers of Maine—an area substantially greater than the size of Ireland—grow 22 distinct cultivars? For those of you in the south, Ireland would fit comfortably in South Carolina. For midwesterners and westerners, two “Irelands” would fit in Wisconsin, and three would fit in Oregon—with Connecticut tossed in. Rather than the Irish farmer in the 1840s, could it be the contemporary potato farmer who best exemplifies a “dependency” on a handful of cultivars?
Thanks to the noted historian Redcliffe Salaman, here is a list of the “top ten” varieties of the nearly two-dozen potatoes grown in tiny Ireland in 1839:
1. Champion aka Congo aka The Cup: a red skinned, cream fleshed, early to mid season, medium sized tuber; extremely popular due to its flavor and nutrition. A bit hard to digest, so it was mainly sold to people in towns and cities where it got above average prices. (A much later progeny of Champion, “Flourball”, proved easier to digest, as well as blight resistant.)
2. Howard aka Cluster aka The Turk: White skinned and white fleshed, great in poor soils, forming medium sized tubers on short stolons in tight clusters. It was very popular with rural people and the poor. It was early to mid season and turned out to be somewhat resistant to blight, i.e., not all plants succumbed, and many were entirely resistant.
3. Irish Apple Red: Red skinned, late and also somewhat long-keeping in storage. Very dry tubers rather than wet—perfect for both boiling and mashing to which milk could be added. Extremely popular and well liked, due to tuber quality and storage, but also because it produced crops in the mid July to late August period when most other varieties of its kind did not. Susceptible to fungal diseases and very hard hit by late blight during the famine, it has virtually disappeared from cultivation.
4. Irish Apple White: White skinned version of #3.
5. Kerr’s Pink aka White Kidney: Very early, small to medium sized tubers with pink skin and white flesh. Could be double-cropped in some areas. Good tuber quality for all-around purposes. Some but not good blight resistance.
6. Lumper aka Leinster Wonder: Extremely productive, versatile variety that was, therefore, popular with the poor. White skinned and white fleshed tubers of medium size and poor to average quality. Early to mid to late season. Minimal resistance to blight. Legendary in famine history due to popularity with poor, who comprised nearly all the starvation dead.
7. The Manly: Medium to large tubers with white flesh and brownish tan skin. Extremely productive main or mid season variety that would produce record weight harvests. Average tuber quality, but was popular due to high yields.
8. The Noble Ox: Very large tubers that some described as “ugly”, some were also misshaped. Dark brown to almost “black” skin and white flesh, very productive with continuous yields mid to late season. Virus resistance and some blight resistance recorded. Used for both human and dairy cow consumption.
9. The Yam aka Surinam: Red skinned with red streaked flesh. Variable sized from medium to large. Was considered very flavorful and attractive, sold well in towns and cities, less in rural areas.
10. The Lapstone Kidney: White skin and tuber, “mid early” which was popular due both to its niche harvest time, and to its outstanding ability to keep well for almost a year in storage. Also, it was medium to higher yielding with high quality, long, medium-sized tubers.
Remember: the potato farmers of Ireland grew more than twice this number of diverse cultivars—hardly the “monoculture” characterized in recent popular history. In fact, they turned out to be the single most influential group of farmers in modern history. It was the tragedy of the Great Potato Famine that spurred worldwide interest in plant genetics and led, indirectly, to the popularization of not only Mendel, but also Darwin.