Glossary: E

Early selection
Selection during an early generation after cross pollination when the selected individuals are heterozygous.
Early selection is usually acceptable in allogamous species but not in autogamous species.
Its advantage is a considerable shortening of the breeding cycle. Its disadvantage is that heterosis may give a false impression of resistance and yield, and that recessive polygenes will remain unexpressed.
These disadvantages are eliminated with late selection.
Echinochloa frumentacea
Japanese barnyard millet. This millet is the fastest growing of any cereal, and can produce a harvest in little more than forty days. It is grown as a minor cereal in the Orient and India, and as a fodder crop in North America where it can produce up to eight crops a year. A fun project for amateur breeders.
Ecology
The study of the interactions of species, or populations, with each other, and with their environment. Ecology makes considerable use of systems theory, and the concept of the ecosystem. It also tends to emphasise the higher systems levels, and the holistic approach.
See also: Pathosystem.
Economics, agricultural
One of the disciplines that make up crop science. Like general economics, agricultural economics can be divided into macro- and micro-economics.
See also: Self-organising crop improvement.
Ecosystem
A biological system that occupies a specified area, and which involves the interactions of all the living organisms in that area, both with each other, and with their environment.
A subsystem of the biosphere, defined by either geographical or biological boundaries.
Ecotype
A local variant that has been produced by selection pressures peculiar to its own locality within the ecosystem. Ecotypes are the result of micro-evolution and natural selection.
See also: cultivar, Landrace, agro-ecotype.
Edaphic
Pertaining to soils.
Eddoe
See: Colocasia esculenta.
Eelworm
The colloquial term for a nematode, or round worm.
Eggplant
See: Solanum melongena.
Elaeis guineensis
The oil palm, which is native to West Africa.
This palm has the highest yield of vegetable oil of any crop. The oil is obtained from the fruit which contains two distinct types of oil. Palm oil is extracted from the soft fruit flesh, which contains 45-55% of oil. Palm kernel oil comes from the seed, which contains about 50% of oil.
This is not a crop for amateur breeders.
Electron microscope
A microscope that uses electrons instead of light. It has the advantage of a far higher resolution that can show virus particles. But it is a very technical and expensive instrument.
Elephant garlic
See: Allium ampeloprasum.
Elephant grass
See: Pennisetum purpureum.
Elletaria cardomomum
Cardamom. This genus is native to S.E. Asia and is a member of the ginger family, Zingiberaceae. The fruits are widely used as a spice, and are particularly prized in Arab countries for adding to coffee.
The plants are open-pollinated and offer scope for amateur breeders located in areas suitable for cultivation.
Elusine coracana
Finger millet, also known as African millet, as well as wimbi, bullo, telebun, and other vernacular names.
It is an important crop in the drier areas of Africa and India, although sorghum and bulrush millet are more drought-resistant. It has a wide range of uses as flour, as an additive to various dishes, and for brewing. In a dry climate, it stores well for up to ten years.
Finger millet is self-pollinated and there are innumerable cultivars in both Africa and India. A suitable crop for amateur breeders, who should start by selecting within local landraces that are mixtures of inbreeding lines.
Emasculation
The physical removal of the anthers from a hermaphrodite flower, or the male flowers from a monoecious plant, in order to prevent self-pollination, and to compel cross pollination.
Alternative methods involve the use of a male-sterility gene, or a male gametocide.
Embryo
An unborn, unhatched, or ungerminated offspring. An embryo normally results from the fusion of a male gamete with a female gamete. However, in plants, nucellar embryos and apomictic seeds are also possible.
See also: Metaxenia.
Emergent property
This concept was first defined by C.D. Broad some eighty years ago. An emergent property is one that emerges at a particular level of complexity, a particular systems level, but which cannot occur at a lower systems level. Thus, the system of locking of the gene-for-gene relationship is an emergent that is possible only at the systems level of the two interacting populations of the pathosystem.
There must be a population of many different locks, and many different keys, if a system of locking is to function. At the lower systems levels of an individual lock, or an individual tumbler within a lock, a system of locking is impossible. The danger of doing research at too low a systems level is that an emergent may not be apparent. This is a major cause of suboptimisation.
Possibly the best example of emergent properties in biology is the schooling of fish, and the flocking of birds. A scientist studying a single fish in an aquarium, or a single bird in an aviary, cannot possibly observe the phenomenon of schooling or flocking because this property emerges only at the systems level of the population.
Empirical science
Science that emphasises facts, as opposed to concepts and theories. Its converse is rationalism. Either extreme constitutes bad science, and good science must be a blend of both facts and theories.
Endemic
1. An endemic species is one that is uniquely present in a locality.
2. An endemic disease is one that is continuously present, as opposed to an epidemic disease, which is intermittently present.
Endive
See: Cichorium.
Endosperm
The nutritive material, usually oil or starch, stored in some seeds.
Endothia parasitica
The fungus that was accidentally introduced to America from Europe early in the twentieth century. It causes ‘chestnut blight’ and it destroyed the wild chestnut forests of North America.
Engineering, agricultural
One of the many disciplines that makes up crop science. It is concerned primarily with agricultural machinery.
Ensete
See: Ensete ventricosa.
Ensete ventricosa
This member of the banana family is grown for food in Ethiopia. Ensete edule is also cultivated for food in this area. These crops are not recommended for amateur breeders.
Entomologists
Scientists who study the science of insects, or entomology.
Entomology
The scientific discipline concerned with the study of insects. Crop entomology is concerned with the study and control of insects that are crop parasites, crop pollinators, or agents of biological control and integrated pest management.
Entropy
The degree of disorder or randomness of the constituents of a system. In a closed system, entropy increases. That is, all energy gradients disappear, and complexity of pattern is reduced to total simplicity of pattern.
Its converse is negative entropy (negentropy). In an open system, negentropy can increase. All living systems are open systems.
Environment
Approximately synonymous with habitat, the environment can be defined as all the external conditions that affect the survival and growth of an organism.
Enzyme
An organic catalyst, which can both promote and control a specific biochemical reaction.
Ephemeral
Short-lived, temporary.
Epidemic
Parasitism at the systems level of the population.
An epidemic may be continuous or discontinuous, and this determines the relative importance of the two kinds of resistance, and the two kinds of infection. A continuous epidemic is sometimes called an endemic but this usage is best avoided.
See also: Epiphytotic, Epizootic.
Epidemic cycle
An epidemic cycle occurs with a discontinuous epidemic, and it concerns the overall development of an individual epidemic, from the initial inoculum of the parasite to its population extinction.
An epidemic cycle normally coincides with a growing season, such as a summer in temperate regions, or a rainy season in the tropics. However, the epidemic cycle of rubber in the Amazon Valley is defined by the deciduous nature of the rubber tree, whose leaf-fall is independent of season in this continuously warm and wet environment.
Epidemiological competence
A parasite can cause an epidemic only if it has epidemiological competence in the area in question. The level of epidemiological competence can vary from one area to another, and from one season to another, and it is controlled mainly by climatic factors such as temperature and humidity.
For example, the maize disease called ‘tropical rust’ (Puccinia polysora) lacks epidemiological competence outside the lowland tropics. Maize cultivars in Europe are highly susceptible to this disease, but they are not vulnerable to it, because of its inability to cause an epidemic in a temperate climate. The susceptibility of these European maize cultivars becomes apparent only if they are cultivated in the lowland tropics.
Variation in epidemiological competence explains the need for on-site selection when breeding for horizontal resistance.
Epidemiology
The study of epidemics, which requires both a holistic and a mathematical approach.
Epidermis
The outermost tissue of leaves and herbaceous stems. The epidermis usually consists of a single layer of cells, often protected by a layer of wax.
The pattern of cells, similar to that of a jigsaw puzzle, is often characteristic of a particular species, and can be used during research for plant identification in animal feces, and in certain forensic situations.
Stomata are a component of the epidermis.
Epiphyte
A plant that lives on another plant without being parasitic. For example, moss and lichen growing on a branch of a tree are epiphytes.
Epiphytotic
A somewhat pedantic term, sometimes used to describe an epidemic in plants, on the grounds that the Greek root demos refers to people. But the term ‘epidemic’ is an English word, and common usage allows it to be applied to plants and animals.
Note that epiphytology is the study of epiphytes, and that the study of epiphytotics is epiphytotiology. These usages are not recommended. See Also: Epizootic.
Epizootic
A somewhat pedantic term (pronounced epi-zoh-otic), sometimes used to describe an epidemic in animals. The study of epizootics is epizootilogy. These usages are not recommended. See also: Epiphytotic.
Eradication
Eradication, like the word ‘unique’, is a word that should be used with caution. Eradication is an absolute, which either does or does not succeed. In the present context, it means the total and complete elimination of a pest or disease, within a stated area.
For example, eradication of the accidental introduction of Colorado beetle of potatoes in Germany was successful, but attempts to eradicate a later introduction in France failed, and this pest then became firmly established in Europe. Occasional appearances of the beetle in Britain have been successfully eradicated.
Eragrostis curvula
A subtropical fodder grass native to Southeast Africa.
Eragrostis tef
This cereal is unique to Ethiopia where it is used for the production of the staple dish ‘njera’. It is also an excellent fodder crop. The self-pollinated flowers are very small and this makes cross pollination extremely difficult. Not recommended for amateur breeders.
Ergotism
The human disease caused by the ingestion of poisonous ergots. The symptoms of ergotism are a constricting of the blood vessels which can lead to gangrene, abortion in pregnant women, and death.
Before the discovery of the cause of this disease, ergots were common in rye produced in a wet summer, and ergotism was a powerful incentive for the cultivation of potatoes in the rye districts of Europe, particularly in eastern Germany, Poland, and western Russia.
Today, ergots are recognised and easily separated from rye before milling. They have a market value in the pharmaceutical industry as an aid to childbirth.
Ergots
Toxic black bodies produced in rye by the fungus Claviceps purpurea. Toxic ergots are also produced by Claviceps penniseti in bulrush millet. When ingested, ergots are the cause of the human disease ergotism.
Erosion of horizontal resistance
A quantitative loss of horizontal resistance. There are four categories of erosion:
1. A host erosion results from genetic changes in the host. This can occur during the cultivation of a genetically flexible crop, but not during the cultivation of a genetically inflexible crop. It can also occur during the breeding of any crop in the absence of a parasite, particularly if the screening population is protected by a functioning vertical resistance or by a pesticide. It is then known as the vertifolia effect.
2. An environment erosion results when a cultivar is taken from an area of low epidemiological competence, and is cultivated in an area of high epidemiological competence.
3. A parasite erosion results from genetic changes in the parasite. This is important only occasionally, and only with facultative parasites.
4. A false erosion results from sloppy experimental work, when a cultivar thought to be resistant is later found to be susceptible.
Erysiphales
The plant-pathogenic powdery mildews, characterised by growing on the external surfaces of plants.
This Order contains six genera defined by the cleistothecia, which may have one or several asci, and various types of appendage: Erysiphe (several asci, simple appendages), Sphaerotheca (one ascus, simple appendages), Microsphaera (several asci, dichotomous appendages), Podosphaera (one ascus, dichotomous appendages), Phyllactinia (several asci, rigid appendages), and Uncinula (several asci and curled appendages).
The imperfect stage, consisting of hyphae and conidia only, is called Oidium.
Erysiphe
A genus of the Erysiphales, or powdery mildews.
The most important species are Erysiphe graminis, which attacks wheat, barley, rye, oats, and many fodder grasses; Erysiphe polygoni, which attacks peas, clovers, and swedes; and Erysiphe cichoracearum, which has a wide host range that includes various cucurbits, tobacco, and many ornamentals.
Vertical resistances are common and there is considerable scope for breeding for horizontal resistance by amateurs.
Erythroxylon coca
Coca, the source of cocaine, native to tropical and subtropical South America.
Escapes from parasitism
See: Chance escape.
Essential oils
This term means ‘essence’ rather than indispensable. Essential oils are obtained from a wide variety of plants, and the oil is extracted either by distillation or by solvents, which are then evaporated off and reused.
Most essential oils are used in the perfume industry and for aromatherapy, but a few also have medicinal uses. Many of them offer scope for amateur breeders who, however, should be aware of the limited markets that are easily saturated.
Ethrel
The trade name for ethephon, which is 2-(chloro-ethyl)-phosphonic acid. It is an ethylene (ethene) generator when applied to plant surfaces. Ethylene has numerous physiological effects, such as inducing synchronous flowering and fruit ripening, which assists mechanical harvesting, etc.
Ethrel is also used as male gametocide to induce random cross pollination for recurrent mass selection in inbreeding cereals such as wheat.
Eucalyptus spp.
A genus of trees, known as gum trees, originating in Australia. These fast-growing trees are an excellent source of firewood in areas that are short of fuel for cooking. They are now widespread throughout the tropics and subtropics. There is considerable scope for amateur breeders to select within existing populations for fast growth.
Eucaryote
All organisms, other than bacteria and cyano-bacteria, are eucaryotes, and they are characterised by consisting of cells that contain a distinct nucleus enclosed in a membrane and containing chromosomes, as well as other specialised organelles.
See also: Procaryote.
Eugenia carophyllus
The clove tree, which originated in the spice islands of the Moluccas, in eastern Indonesia.
The cloves of commerce are the dried, unopened buds, and they became a monopoly of the Portuguese in the early sixteenth century. The Dutch gained the monopoly in 1605, and kept it for two centuries. Later, cloves were taken to many areas, but they flourished best in Zanzibar, which became the main producer.
Cloves are now grown increasingly in Indonesia, where they are in great demand for clove cigarettes.
Evergreen
Evergreen trees and shrubs have persistent leaves and continuous pathosystems and, consequently, a gene-for-gene relationship and vertical resistance will not evolve in them. A gene-for-gene relationship can evolve only in a discontinuous pathosystem. See also: Deciduous.
Evolution
The results of natural selection, often described as the survival of the fittest.
Macro-evolution (or Darwinian evolution) occurs during periods of geological time, and involves genetic changes that are both new, and irreversible. New species are formed by macro-evolution. Macro-evolution also produces an increase in complexity, and new genetic code.
Micro-evolution occurs during periods of historical time, and it involves genetic changes that are not new, and that are reversible. It does not increase complexity, but merely reorganises existing complexity. Nor does it produce new genetic code; it merely rearranges existing code.
The formation of ecotypes is micro-evolution by natural selection, and the production of cultivar or agro-ecotypes, by plant breeding is micro-evolution by artificial selection.
The mechanism of evolution has long been disputed and is now thought to be the result of natural selection operating on emergents at all systems levels.
Examples of horizontal resistance
See: horizontal resistance, examples.
Exobasidium vexans
The fungus that causes blister blight of tea. There is great scope for selection for horizontal resistance within existing crops grown from true seed, as these crops constitute a vast hybrid swarm.
Exoskeleton
The hard external surface of all arthropods, including the insects. Because the exoskeleton cannot expand or grow, it must be shed or moulted at several stages during the growth of the individual arthropod. See also: Instar.
Extension service
The service that provides technical and specialised information to farmers. In the USA, the extension officers are known as county agents. It is rare that they are trained in alternative techniques like organic farming and horizontal resistance breeding.
Extensive crop
A crop that has low production costs and profit margins. Soybeans, maize, and wheat are typical extensive crops in North America.
See also: intensive crop.
Extinct wild progenitors
Crops whose wild progenitors have been harvested by ancient hunter-gatherers to extinction.
The domesticated forms survived because farmers are always careful to preserve propagating material of their crops. But food gatherers may be careless about wild plants and, in the course of a few human generations, they may not have noticed the decline in numbers that was occurring because of their activities.
Among ancient clones, this loss of wild progenitors has occurred with black pepper, garlic, ginger, olive, saffron, and turmeric.
Among other crops, a loss of wild progenitors also occurred with broad bean, cassava, chillies, green peas, onions, peanuts, soybean, sweet potato, tea, turmeric and yams.
Extinction
The total loss of a species resulting from either natural competition, or the activities of humankind.