question: How do humans selectively breed plants?
comment: Let's say you have a whole bunch of jalapeno pepper plants. Like, 100 plants. After the season's over, let's say you were keeping track of all of the peppers and their qualities. Maybe one plant produced slightly more peppers. Maybe one plant grew slightly bigger jalapenos. Maybe one plant grew slightly spicier jalapenos on average. So, let's say you don't necessarily want spicier peppers, but you'd like more bang for your buck in the form of more peppers per plant, and larger peppers. So, you take the seeds from the largest plants and the plants with the highest output and plant those next year. Insects cross-pollinate between the two. Do the same thing this year and select the best-performing plants, take seeds from those peppers and use them next year. Rinse and repeat over a long period of time, and you may start noticing improvements over when you started. This is selective breeding.
passages: Under our system of plant breeding we carry the mating of varieties or breeds far beyond what is practised in the animal kingdom. In the first instance we mate varieties and also what were formerly regarded as distinct species of the same genera, and after fixation, the progeny by these combinations are further mated together. 
  
  A further extension of our system which is in itself unique and instructive, is the mating of uncultivated indigenous plants of the same Natural Order as the cultivated varieties. From such combinations most valuable results have been obtained. 
   Another part of our system is the improvement of existing varieties of agricultural plants. The method is similar to that adopted by the breeder of stock for the improvement of his animals, when fresh blood of the same breed is introduced from some other herd. 
  
  By crossing two distinct plants of the same variety the resulting progeny is more vigorous and robust in constitution, whilst the habit and individual character of the variety is maintained. 
  
  A year later, these Explanatory Notes come from the Gartons Seed Catalogue for Spring 1901:
   Section::::Methodology.
  
  Plants are bred using one of two main methods:
  
  Section::::Methodology.:Selective breeding.
   Section::::History.
  
  According to garden historian Paige Johnson 
  
  Section::::Comparison to other agronomic techniques.
   By mating the varieties of this species with cultivated varieties, new breeds have been produced which will under no conditions shed their seed when ripe, but which thresh out a perfectly clean sample with a much heavier yield per acre than common wheat. 
   Section::::Modern plant breeding.:Genetic modification.
   Plant breeding has been practiced for thousands of years, since near the beginning of human civilization. It is practiced worldwide by individuals such as gardeners and farmers, and by professional plant breeders employed by organizations such as government institutions, universities, crop-specific industry associations or research centers.
  
  International development agencies believe that breeding new crops is important for ensuring food security by developing new varieties that are higher yielding, disease resistant, drought tolerant or regionally adapted to different environments and growing conditions.
  
  Section::::History.
   Modern plant breeding may use techniques of molecular biology to select, or in the case of genetic modification, to insert, desirable traits into plants. Application of biotechnology or molecular biology is also known as molecular breeding.
  
  Section::::Modern plant breeding.:Marker assisted selection.
   Section::::Addressing global food security through plant breeding.:Breeding for tolerance.
   To illustrate the modificability you can take a look at our cultivated plants. The harvest of those plants do not only depend on the quality of the seeds but also greatly on environmental factors like the condition of the soil, the nutrient content of the soil, the fertilization, the humidity and temperature as well as the interference of other plants.
  
  Section::::Example.
   In countries that experience harsh winters such as Iceland, Germany and further east in Europe, plant breeders are involved in breeding for tolerance to frost, continuous snow-cover, frost-drought (desiccation from wind and solar radiation under frost) and high moisture levels in soil in winter.
  
  Section::::Participatory plant breeding.
   BULLET::::5. Increased tolerance to insect pests
  
  BULLET::::6. Increased tolerance of herbicides
  
  BULLET::::7. Longer storage period for the harvested crop
  
  Section::::Classical plant breeding.:Before World War II.
  
  Successful commercial plant breeding concerns were founded from the late 19th century. Gartons Agricultural Plant Breeders in England was established in the 1890s by John Garton, who was one of the first to commercialize new varieties of agricultural crops created through cross-pollination. The firm's first introduction was Abundance Oat, one of the first agricultural grain varieties bred from a "controlled" cross, introduced to commerce in 1892.
   The hardiness of constitution, standing power of straw, and remarkable fertility of the wild or land oat, Avena fatua, of Great Britain have been successfully introduced, but not without many difficulties, into some of the new breeds.
  
  Some progress has also been made with the improvement of existing varieties of Agricultural plants by introducing pollen from plants of the same variety to increase the vigour of the plant without materially altering its general characteristics.
  
  Section::::Varieties Bred and Introduced.
  
  Barley Varieties:
   Classical breeding relies largely on homologous recombination between chromosomes to generate genetic diversity. The classical plant breeder may also make use of a number of "in vitro" techniques such as protoplast fusion, embryo rescue or mutagenesis (see below) to generate diversity and produce hybrid plants that would not exist in nature.
  
  Traits that breeders have tried to incorporate into crop plants include:
  
  BULLET::::1. Improved quality, such as increased nutrition, improved flavor, or greater beauty
  
  BULLET::::2. Increased yield of the crop
  
  BULLET::::3. Increased tolerance of environmental pressures (salinity, extreme temperature, drought)
  
  BULLET::::4. Resistance to viruses, fungi and bacteria
   Section::::Growing process.:Greenhouses/nurseries.
   Section::::Asexual propagation.
  
  Plants have a number of mechanisms for asexual or vegetative reproduction. Some of these have been taken advantage of by horticulturists and gardeners to multiply or clone plants rapidly. Humans may utilize these processes as propagation methods, such as tissue culture and grafting. Plants are produced using material from a single parent and as such there is no exchange of genetic material, therefore vegetative propagation methods almost always produce plants that are identical to the parent. Vegetative reproduction uses plants parts such as roots, stems and leaves. 
   Plant breeding has been used for thousands of years, and began with the domestication of wild plants into uniform and predictable agricultural cultigens. High-yielding varieties have been particularly important in agriculture.
  
  Selective plant breeding is also used in research to produce transgenic animals that breed "true" (i.e., are homozygous) for artificially inserted or deleted genes.
  
  Section::::Selective breeding in aquaculture.
   Although the natural laws which govern the Animal and the Vegetable Kingdoms bear a very strong resemblance to each other, further points can be realised and greater progress can be made in a limited time with plants than with animals under a system of cross breeding. 
  
  Not only have varieties of a given species, but what were formerly regarded as distinct species belonging to the same genus, been successfully mated. 
   Section::::Modern plant breeding.:Reverse breeding and doubled haploids (DH).
   The most common form of plant reproduction utilized by people is seeds, but a number of asexual methods are utilized which are usually enhancements of natural processes, including: cutting, grafting, budding, layering, division, sectioning of rhizomes, roots, tubers, bulbs, stolons, tillers, etc., and artificial propagation by laboratory tissue cloning. Asexual methods are most often used to propagate cultivars with individual desirable characteristics that do not come true from seed. Fruit tree propagation is frequently performed by budding or grafting desirable cultivars (clones), onto rootstocks that are also clones, propagated by stooling.
   Genetic modification of plants is achieved by adding a specific gene or genes to a plant, or by knocking down a gene with RNAi, to produce a desirable phenotype. The plants resulting from adding a gene are often referred to as transgenic plants. If for genetic modification genes of the species or of a crossable plant are used under control of their native promoter, then they are called cisgenic plants. Sometimes genetic modification can produce a plant with the desired trait or traits faster than classical breeding because the majority of the plant's genome is not altered.
   FOR over 20 years the work of cross-fertilising crop plants, with the object of producing New and Improved Breeds, has been carried on at Newton-le-Willows in Lancashire. It has there for the first time been demonstrated to Scientific Botanists as well as to Agriculturists that all the corn crops (cereals) and nearly all the other common crops of the farm are self fertilising. In other words, each individual plant provides the pollen which is required in the process of producing seed, to fertilise the female organs of its own flowers. This natural process results in a perfect system of in-breeding which has been going on for an indefinite period, making it possible to grow the different varieties of crops of the same kind in close proximity to each other, and even as mixed crops without any danger of crosses being produced. 
   Chemical mutagens like EMS and DMS, radiation and transposons are used to generate mutants with desirable traits to be bred with other cultivars – a process known as "Mutation Breeding". Classical plant breeders also generate genetic diversity within a species by exploiting a process called somaclonal variation, which occurs in plants produced from tissue culture, particularly plants derived from callus. Induced polyploidy, and the addition or removal of chromosomes using a technique called chromosome engineering may also be used.
   Section::::Conditioning.:Hardening off, frost hardiness.
   For future agriculture to thrive there are necessary changes which must be made in accordance to arising global issues. These issues are arable land, harsh cropping conditions and food security which involves, being able to provide the world population with food containing sufficient nutrients. These crops need to be able to mature in several environments allowing for worldwide access, this is involves issues such as drought tolerance. These global issues are achievable through the process of plant breeding, as it offers the ability to select specific genes allowing the crop to perform at a level which yields the desired results.
  