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When the harvest was good, Irish peasants often ate 8—14 pounds 3—6 kilograms of potatoes a day and with little else, unless some milk was available from a cow. Although decidedly boring, this daily intake provided substantial nutrition, including protein, carbohydrates, and many vitamins and minerals—particularly, vitamin C.

Figure 1. Map of South America. The potato originated in the region around Lake Titicaca, between Peru and Bolivia. Harvesting potatoes in Maine in the early s. Potato plants produce an abundant and nutritious food supply. The grain crops, which grew poorly in Ireland anyway, were needed to pay the rent to the landowners, most of whom lived in England. In contrast to the wealthy landowners, most peasants lived in one-room, windowless huts with dirt floors, holes for a door and in the roof to let smoke from the fire escape, and little furniture or other possessions.

Fortunately, potatoes thrived in the cool, moist climate of Ireland, which was similar to that of the South American highlands, their place of origin. A family could grow enough potatoes to feed themselves on half the land required to produce the same number of calories in grains Figure 1.

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The Potato Plant: Valuable Tubers A field of growing potato plants is a beautiful sight, especially in midsummer, when the plants begin to bloom. The leaves on the bushy plants are composed of a number of dark-green, leaflike sections called leaflets, which are connected to a central petiole and therefore called compound leaves Figure 1.

Each plant has a bud at the growing tip and lateral side buds, where the leaves attach to the main stem. If the top of the plant is pinched off, the lateral buds begin to grow. Pinching off the top is a common practice for producing bushier house plants and other ornamental plants.

The flowers on potato plants may not be familiar to someone who has not seen potato fields. After blooming, fertile plants produce green berries that are similar to small tomatoes and filled with numerous tiny seeds. Rejection of these small, bitter fruits as food was probably another reason for the slow acceptance of this crop in Europe. The potato is in the botanical family Solanaceae, which also includes bell and hot peppers, eggplant, petunia, tobacco, tomato, and some poisonous members, such as deadly.

The potato, Solanum tuberosum. Left, an entire plant. Right top, flower. Right bottom, fruit berries. The Solanaceae family is worldwide in distribution, but some members—such as potato, tobacco, and tomato—are native to Central and South America and were unknown to Europeans before they began exploring Scientific names the Western Hemisphere.

The similarities in flower strucThe Latin binomial was devised by students ture make the relations among these plants clear, even of Linnaeus, who were assigned to write though they differ in other characteristics. The family down all the plants fed on by grazing aniname is derived from the Latin solamen, which means mals. Deadly names in use at the time, so they shortened members of the family slowed the acceptance of the edithe names to just two words. Until that time, ble members as food plants, but eventually, they were there was no standard format for naming discovered to be safe.

Some toxic alkaloids are present in species, and the use of long, cumbersome the leaves of potato plants, causing digestive upsets to definitions made communication between those who eat them. If potato tubers are left in the light, biologists difficult. All organisms are given a similar Latin bisufficiently different to be considered different nomial two-word name based on a system created in the species.

The second word is the specific epis by the famous Swedish naturalist, Carolus Linthet: a descriptive word that separates this naeus. Because tubers grow underground, they might apspecies from all others in that genus. Roots do not produce underlined when written. Once the genus has buds and leaves or turn green when left in the light. Tubeen written out in full, it can be abbreviated bers are actually underground stems adapted to the storin subsequent appearances, using the upperage of nutrients.

After several months in storage, the buds case first letter followed by a period and the on potato tubers begin to sprout and are ready to grow inspecific epithet, as in S.

These swellings are new tubut our expanding knowledge of the variety bers, which store the excess food the plant produces durof life has made this definition difficult to ing photosynthesis. The starchy tubers may be harvested apply in the case of many microorganisms. As the mature vines die aboveground, the tubers develop an outer cork layer for survival in the soil during the winter.

This layer also protects them from desiccation and wounding when they are harvested and put into storage. Stored potatoes must be kept cool to prevent rotting by bacteria and fungi present on the tubers. Most commercial potato growers and home gardeners do not plant the tiny seeds from the green berries produced after flowering. Instead, potatoes are grown by vegetative propagation; that is, small tubers or pieces of tubers are planted.

To maximize the planting stock, farmers may cut each tuber into several pieces. Each piece can grow into a new. Vegetative propagation has several advantages. In addition, each tuber piece grows into a plant that is genetically identical to the parent plant in size, time to maturity, and other important characteristics, including tuber taste and texture. True botanical seed, from the fruit of a plant, is the product of sexual reproduction, which results in genetic variation.

Each seed produces a plant that is slightly different from its parents and all of its siblings. Genetic uniformity is a great advantage when uniformity has an economic benefit—as in flowers, fruits, ornamental plants, and some vegetables—so vegetative propagation has become a common practice in modern agriculture Table 1. Tubers also provide an advantage to wild potato plants, because they help ensure survival in case the true seeds produced in the berries do not grow successfully.

There are, however, some disadvantages to vegetative reproduction of agricultural crops. The advantages of uniform characteristics may be outweighed by the disadvantage of uniform susceptibility to pests and pathogens. If one plant in a field is vulnerable to a particular disease, then so are all of its neighbors. Genetic uniformity increases the risk of loss. A second important risk lies in the large pieces of plant tissue that are planted during vegetative reproduction.

Bulbs, cuttings, roots, tubers, and other relatively large plant pieces may be planted, rather than tiny seeds. These large plant pieces often carry pathogens, especially viruses and other systemic parasites, into the planting area at the very beginning of the season. Many of these pathogens would not be present in true seed, produced by sexual reproduction. The yield and quality of the crop may be greatly reduced by the introduction of pathogens on or in plant parts.

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Of course, many kinds of parasites were not discovered or well understood until relatively recently, but farmers of the past observed the ravages of the diseases the parasites caused. Farmers suspected that reduced yields were related to the use of vegetative reproduction, which, despite its convenience, was conTable 1.

They believed that sexual Yams Dry broad beans 1. Sweet potatoes Wheat 1. Used by velop potato cultivars suitable for permission of CIP. As a result, the genetic variation among the potato cultivars was very limited. Crop losses occurred every year from various causes, and occasional food shortages were not unusual.

When crops were good, tubers were plentiful in the months after the harvest, but as the winter months passed, supplies diminished and the tubers began sprouting, ready to plant for the next crop but no longer suitable for food. The summer months were a hungry time, usually requiring the Irish peasants to spend what few coins they had for grain to feed themselves until the next potato harvest.

What were the important components that led to the tragedy? The human component should always be considered, and in this case, a large population depended on a single food crop. The Irish population had grown rapidly following the introduction of the potato, and no significant alternative foods existed when the crop failed. The grain crops the Irish planted were needed to pay the rent to the English landlords. If the rent was not paid, the people were thrown off their land and faced certain starvation. Perhaps this dependence on one crop for food sounds foolish or risky today, but the current human population, now approaching 7 billion, relies on essentially three species of plants—wheat, corn, and rice—to feed most of its people, an issue we will return to in Chapter In addition to the human component, we should consider the important biological components that combined to cause the blight of the potato crop.

Plant pathologists have devised a memory aid called the disease triangle Figure 1. The potato crop was derived from a small supply of tubers that survived the lengthy trip across the sea to Europe. They particularly favored one type of potato called Lumper. From the name, it is obvious that this cultivar was not grown for the beauty of its tubers but rather for the large quantity of food produced.

Thus, every plant in every field was nearly genetically identical—a desirable situation for agricultural characteristics, such as high yield to feed a large family, but a potentially dangerous situation for disease development. For the early weeks of summer in in Ireland, records show hot and dry weather overall.

Then the weather changed. Overcast skies dominated for 6 weeks, along with low temperatures.