unit two Plant Structure, Chemistry, Growth, Development

1
unit two Plant Structure,Chemistry, Growth,
Development, Genetics, Biodiversity, and Processes
6 Structure of Higher Plants  7 Plant Growth
Development   8 Plant Chemistry Metabolism 9
Genetics Propagation 10 Cultivated Plants
Naming, Classifying, Origin, Improvement
Germplasm Diversity and Preservation  11
Photosynthesis Respiration   12 Water
Relations   13 Mineral Nutrition  
2
KEY LEARNING CONCEPTS
After reading this chapter, you should be able to

• Explain how plants are named and classified.

• Use the nomenclature and system of taxonomic
  classification to identify plants and their
  relationship to each other.
• Explain how several crops originated and where
  they were domesticated.
• Discuss the importance of saving germplasm from
  extinction and the global system created to
  preserve germplasm.

3

• There are over 500,000 different kinds of plants.
  
• The first recorded names were attributed
  toTheophrastus (370285 bce).

• Naming plants began with simple names
  referringto the plants use, growing habit, or
  other attribute.
• A difficulty is that often names are only used
  locally.
• Any system of classifying plants depends on how
  the classification is to be used.

4
Climatic and Related Classifications

• Farmers and others who grow plants commercially
  have to be able to identify and name crops.
• And distinguish which crops and plants suit their
  climate.
• Plants can be classified into distinct groups by
  climate.

• The USDA has divided the U.S into several
  different cold hardiness zones many plants are
  classified by their ability to grow in the
  different zones.
• Some annuals have specific climatic requirements,
  and are distinguished as winter or summer
  annuals.
• Winter annuals are planted in the fall, and bloom
  earlythe following spring.
• Summer annuals are planted in the spring, and
  bloom through the summer and fall.

5
Climatic and Related Classifications

• Some crops grow best in certain seasons.

• Warm-season plants grow best where monthly
  temperatures average 65- 80 F.
• Corn, beans, tomatoes, peppers,, petunias,
  marigolds, zinnias.
• Cool-season crops grow best at average monthly
  temperatures average 60-65 F.
• Broccoli, cabbage, peas, flowering bulbous
  plants, cyclamen.

• Numerous flower and vegetable cultivars can be
  classified as early, midseason, or late maturing.
• Plants can be classified by the seasons in which
  they are most likely to flower and fruit.
• Or when product quality can be expected to be
  maximum.
• Many can be classed early, midseason, or late
  maturing

6
Climatic and Related Classifications

• Vegetables are classified into groups according
  to their edible parts.

• Ornamentals are sometimes classified by use, as
  are plants outside the home.
• Houseplants are often classified according to
  their foliage, flowers, or growth habits.

7
Climatic and Related Classifications

• Foresters classify trees into two broad
  groupshardwoods and softwoods.

• Some hardwood types are oaks (Quercus), maples
  (Acer), birch (Betula), and beech (Fagus).
• Some softwood trees are pines (Pinus), cedars
  (Cedrus), redwood (Sequoia), and spruce (Picea).

• Trees are also classified according to the
  hardiness zones in which they can survive.

8
Climatic and Related Classifications
9
Common and Botanical Names

• Most plants are generally known by their common
  nameseasier to remember, pronounce use.
• Names often evolve due to certain plant
  characteristics.

• A common name has value in conversation only if
  both persons know exactly what plant is being
  discussedmost likely with persons from the same
  community the plant name cannot be mistaken.

10
Common and Botanical Names

• JASMINE - AN EXAMPLE

Star jasmine(Jasminum gracillimum) Star
jasmine(Trachelospermum jasminoides) Blue
jasmine (Clematis crispa) Cape jasmine (Gardenia
jasminoides) Crape jasmine (Tabernaemontana
divaricata) Night jasmine (Cestrum
nocturnum) Night jasmine (Nyctanthes
arbor-tristis)
Many common plant names contain the word
jasmine,but do not resemble oneanother, and may
not beclosely related botanically.
11
Development of Botanical Classifications

• Theophrastus (370285 bce), a student of
  Aristotle, classified plants by their texture or
  form.
• He classified many as herbs, shrubs trees,
  noted annual, biennial perennial growth, and
  described differences in flower parts.

• Carl von Linné (17071778), devised a system of
  categorizing plants that led to the modern
  taxonomy or nomenclature of plants.

12
Scientific Classification

• The scientific system classifies living things by
  groupstaxabased on physical characteristics.

• The first taxon, Domain, divides living things
  into
• Prokaryotes (cells having no separate subcellular
  units).
• Eukaryotes (cells having subcellular units).
• The Eukaryote Domain is divided into the
  Kingdoms
• Fungi, Protista, Plantae, and Animalia.
• The Plantae Kingdom is divided into
• Bryophytes (includes mosses and liverworts)
• Vascular plantsdivided by seedless and seeded.

13
Scientific Classification

• Seedless seeded plants are classed by Phyla.
• Seedless phyla include the Pterophyta (ferns).
• Seeded phyla include Cycadophyta (cycads),
  Ginkgophyta (ginkgo), Coniferophyta (conifers),
  and Anthophyta (angiosperms).

• After phylum, plants are classified in descending
  rank by class, order, family, genus, and species.
  
• Each descending rank more closely defines the
  physical characteristics common to members of
  that rank.

14
Plant Identification and Nomenclature

• The family is usually the highest taxon commonly
  included in plant identification or study.
• Students are usually required to learn family,
  genus, and species of some plants, as well as
  their common names.

• Since the early Christian era, naturalists wrote
  their books in LatinLinnaeus used names of Latin
  form.
• Most names he gave are phonetic,and give a clue
  to plant characteristics, native habitat, or for
  whom it is named.

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Plant Identification and Nomenclature

• Names that refer to leaves include folius,
  phyllon,or phyllausually as suffixes.
• Names can also have prefixes, such as macro or
  micro.

• Words are created
• macrophylla (large leaf).
• microfolius or microphylla (small leaf)
• illicifolius (holly leaf) salicifolius (willow
  leaf).

The Latin for flower is flora addthe prefix
grand, and it becomes grandiflora (large flower),
as in Magnolia grandiflora L. The southern
magnolia
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Plant Identification and Nomenclature

• Shapes or growing habits of plants are described
• altus or alta (tall), arboreus (treelike),
  compactus (dense).
• nanus or pumilus (dwarf), repens or reptans
  (creeping).
• scandens (climbing).

• Names based on flower or foliage color
• albus or leuco (white), argentus (silver).
• aureus or chryso (gold), rubra, rubens, or
  coccineus (red)
• croceus, flavus, or luteus (yellow).

17
Plant Identification and Nomenclature

• Species names sometimes reflect the plants place
  of origin.

• australis (southern), borealis (northern).
• campestris (field), insularis (island), montanus
  (mountain).
• canadensis (from Canada).
• chinensis or sinensis (from China).
• chilensis or chileonsis (from Chile).
• japonica, nipponica, or nipponicus (from Japan).

18
Plant Identification and Nomenclature

• Each plant has a two-wordbinomialLatin name,
  which is international, and understood
  universally.
• The first name refers to the genus the second,
  its species.

• Complete Linnaean names have a third
  elementauthoritythe abbreviated name of the
  scientist who named the species.
• Wild or naturally occurring plants are named
  under the International Code of Botanical
  Nomenclature.
• Cultivated plants are covered by the
  International Code of Nomenclature for Cultivated
  Plants.

19
Plant Identification and Nomenclature

• Basic rules of nomenclature

• The generic name always begins with a capital
  letter itis underlined if hand- or
  type-written, italicized in print.
• The specific epithet usually begins with a
  lowercaseletterbut may be capitalized if it is
  a persons name.
• To complete the binomial name, authority for
  describing and naming the plant is given after
  the genus and species.
• Authority names are often abbreviated and
  taxonomybooks have a list of the full names of
  these authorities.
• When several plants in the same genus are listed,
  the genus name is given in full for the first,
  then shortened to the first initial (capitalized)
  for the other plants in the list.
• This procedure should not be used if there is any
  chanceof confusion with another genus with the
  same first initial.

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Plant Identification and Nomenclature

• Occasionally the genus is known but the exact
  species is not.
• In such a case, the genus is given, followed by
  lowercase letters sp. for species (singular)
  and spp. (plural).
• The singular and plural spelling of species is
  the same.
• The sp. or spp. is never underlined or
  italicized.

21
Subspecific Categories

• Sometimes a botanical binomial is not sufficient
  to identify a specieswild or cultivated.
• Botanists and horticulturists may form
  subspecific categories, such as botanical
  variety, cultivar, and group.

22
Botanical Variety

• A plant group can be so different in the wild
  fromthe general species it warrants a botanical
  variety classification below that of species.
• An example is Buxus microphylla Sieb. and Zucc.
  var. japonica Rehd. and Wils.
• The var. stands for varietas, Latin for
  variety.

• When a varietas epithet is formed from a
  surname,it may or may not be capitalized
  depending on the personal preference of the
  author.
• The trend is to not capitalize them, as
  recommended by the International Codes.

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Cultivar

• There are two main categories of cultivarsthe
  clones and the lines.
• The word cultivar is abbreviated cv. the
  plural is cvs.

• A cultivar is often a distinct variant selected
  because it was uniquely different from any plant
  in cultivation.
• The cultivar name is always capitalized but never
  underlined or italicized.
• Either single quotes or the term cv. is used,
  but never both.
• Tables or lists usually use cultivar or cv.
  in theheading to avoid single quotes around each
  name.

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Group

• The group category is used for some vegetables
  some ornamentals like lilies, orchids, roses
  tulips.
• Below species, not used as frequently as the
  cultivar.

• A group includes more than one cultivar of a
  particular kind of plant.
• When a species has many cultivars, cultivars that
  are similar are categorized into groups.

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Family

• The family is a group of closely related genera.
• Relationship can be based on plant structures or
  chemical characteristics, but flower structure is
  the usual basis.

• The first letter of family names is always
  capitalized and names are sometimes underlined or
  italicized.
• Family names may be written entirely in capital
  letters.

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Family

• The nightshade family SOLANACEAEincludes

Potato flower
Solanum (potato) Lycopersicon (tomato) Capsicum
(pepper) Nicotiana (tobacco) Datura (deadly
nightshade) Petunia, and many others.
Tomato flower
All species in this family have similar flower
structures, as shownin the similarities between
a potato flower and a tomato flower.
27
Family

• Most families names end with -aceae (ace-ay-ee)
  attached to a genus name,
• Eight families did not follow this standard rule,
  andnew names have been adopted for these
  families.

28
Plant Identification Key

• Keying plants is a process of elimination by
  making yes or no decisions to characteristics
  offered in the keyrejecting those that do not
  apply (dichotomy).
• To use a key you need to know the vocabulary of
  plant structure.

• To use a key, eliminate the alternative that does
  not pertain to the plant in question proceed to
  the next pair of numbers directly under the
  proper choice.
• This procedure is followed until the plant to be
  identified fits a given set of plant
  characteristics.

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Plant Identification Key

• Certain plant parts might not be available
  because of seasonwhen needed to identify the
  plant.
• It might be necessary to preserve flowers for
  future examination or describe them thoroughly
  when abundant.
• Then wait for the fruit to develop to accurately
  determine its characteristics.

• Family characteristics are determined by
  observing and studying certain flower
  characteristics.
• Once the family is known, species are
  identified by referring to taxonomic books with
  detailed keys.

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Plant Identification Key

• Simplified dichotomous key used to identifysome
  commonly known seed-bearing plants
  (Spermatophyta).

See the entire table on pages 203-204 of your
textbook.
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Plant Identification Key

• Examples of hard-to-classify plants.

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Plant Identification Key

• Examples of hard-to-classify plants.

33
Plant Identification Key

• Examples of hard-to-classify plants.

34
Origin of Cultivated Plants

• Most crop plants important today were
  cultivatedin a primitive way long before
  recorded history.

• Most are still cultivated, but in much improved
  forms.
• Others unknown to early humans have been added to
  make our present-day selection of food plants.
• Much later, people became more concerned about
  aesthetics added shade trees, shrubs, flowering
  plants lawn grasses to the list of cultivated
  plants.
• Swiss botanist Alphonse DeCandolle wrote Origin
  of Cultivated Plants, first published in 1833.
• Russian plant geneticist Nikolai Vavilov
  published The Origin, Variation, Immunity, and
  Breeding of Cultivated Plantstranslated from
  Russian in 1951.

35
Origin of Cultivated Plants

• Vavilov concluded that various cultivated plants
  originated in eight independent centers.

• Central China India Indochina and Malay
  Archipelago.
• The TurkeyIran region The Mediterranean area.
• The EthiopiaSomaliland area of east Africa.
• Mexico and Central America
• The PeruEcuadorBolivia and BrazilParaguay
  area.

36
Domestication of Plants

• There is evidence that agricultural villages
  existed about 8000 to 9000 bce in the Fertile
  Crescent.
• Radiocarbon dating suggests animals were being
  domesticated in this area by at least 5000 to
  6000 bce.

• An indigenous savanna type agriculture was
  developing from domesticated native plants about
  4000 bce in a belt across central Africa.
• The first home of the human race, as we know it
  now.
• The Chinese center of agricultural origins became
  important about 4000farming culture in southeast
  Asia Indonesia domesticated rice about 6000 bce.

37
Domestication of Plants

• In the New World, evidence from archeological
  sites shows agricultural beginnings in two areas.

• One is present-day southern Mexico and Central
  America.
• Where plant cultivation began about 5000 to 7000
  bce.
• The second is a broad noncenter stretching from
  Chile northward to the Atlantic Ocean and
  eastward into Brazil.

• No major cultivated crop originated in the area
  of the present-day U.S.agriculture here relies
  in a large measure on introduced crops.
• The only food crop to originate in the continent
  of Australia was the macadamia, or Queensland nut.

38
Domestication of Plants
39
Vegetative or Asexual Propagation Methods

• Some of the oldest cultivated woody plants are
  the easiest to propagate by vegetative methods
  suchas hardwood cuttings.
• Grape, fig, olive, mulberry, pomegranate, and
  quince.

• Many types of ancient plants brought domesticated
  by early people were easily maintained
  increased by unsophisticated vegetative methods.

40
Seed or Sexual Propagation Methods

• Domestication of seed-propagated plants probably
  began as purposeful harvesting of wild grass
  seeds.
• Some of which were sown to produce the next
  years crop.

• In cereals, this procedure starts to separate the
  shattering typesthe seed separates from the
  headfrom the nonshattering types.
• Most of the seeds that shatter fall to the
  ground, while nonshattering seeds are harvested
  and can be resown.
• Planting harvested seeds closely in a cultivated
  plot kept free of competing weeds automatically
  selects for the stronger, more vigorous plants.

41
Seed or Sexual Propagation Methods

• Desirable characteristics arising from selection
• Loss of seed dormancy, increased flower
  numbersand larger inflorescences.
• Trends toward determinate growth.

42
Improvement in Some Important Crop Plants

• Present, improved cultivars of important
  cropshave been so adapted to conform to
  humancultural practices that they all now
  completely depend on our care for their continued
  existence.

43
Grains and Vegetable Crops

• Wheat(Triticum aestivum and T. turgidum Durum
  group)

• The most widely cultivated plant in the world
  today, the chief cereal, and is used worldwide
  for making bread.
• Evolved from wild wheatlike grass found and
  cultivated by ancient humans in the Near East
  region about 7000 bce.
• Probably improved by spontaneous hybridizations,
  by chromosome doubling mutations to increase
  fertility.
• Species occur in a series with increasing
  chromosome numbers.
• Breeders have developed dwarf forms of wheat,
  whichcan produce high seed yields without
  falling over (lodging).
• From the Near East, early wheat forms were taken
  into ancient Egypt, the Balkans, and central
  Europe.
• The Spanish brought wheat to the Americas.

44
Grains and Vegetable Crops

• Wheat(Triticum aestivum and T. turgidum Durum
  group)

• Introduction of Turkey Red wheat by Russian
  immigrants established the U.S. hard red winter
  wheat industry.

• The two major wheat species today are
• Triticum aestivumused for flour in making breads
  and pastries
• T. turgidum (Durum group)for macaroni, spaghetti
  noodles.
• Wheat cultivars resistant to the devastating stem
  rust disease must continually be developed to
  cope with the mutating stem rust pathogen.
• Wheat plants are self-pollinated, allowing
  farmers tosave their seeds for future planting.
• Wheat has perfect (bisexual) flowers, making
  crosspollination difficult.

45
Grains and Vegetable Crops

• Corn(Zea mays)

• Originated in the New World about 5000 to 6000
  bce.
• Probably in several places in both Mexico and
  South America.
• Maize is known only as a domesticated plantthere
  isno wild form except, apparently, teosinte, a
  close relative.
• Economic life of the ancient American
  civilizationsthe Aztecs, Mayas, and
  Incasdepended on corn.
• At the time of Columbuss expeditions to the New
  World,corn was being grown by Indian tribes from
  Canada to Chile.
• Corn mutates easily, forming new types.
• Even today, it is an extremely variable species,
  from grain color, to the size shape of the
  grains ears.

46
Grains and Vegetable Crops
Hypotheses advanced to explain the origin of corn

• It developed from pod corn, a type in which
  each individual kernel is enclosed in floral
  bracts.
• It originated from teosinte, by gradual selection
  underthe influence of harvesting by humans
• Corn, teosinte Tripsacum (a perennial grass)
  descended along independent lines directly from a
  common ancestor.
• A tripartite theory that
• (a) cultivated corn originated from pod corn.
• (b) teosinte is a derivative of a hybrid of corn
  and Tripsacum.
• (c) the majority of modern corn cultivars are the
  product of an admixture with teosinte or
  Tripsacum, or both.

47
Grains and Vegetable Crops

• Corn(Zea mays)

• The development of hybrid corn in the 1930s is
  one ofthe outstanding achievements of modern
  agriculture.
• In 1935, 1 of corn planted in the U.S. was of
  the hybridtypeby 1970, almost all corn produced
  was hybrid.

• Hybrid cultivars, along with fertilizers,
  irrigation, and mechanization, dramatically
  improved production.
• Corn is now one of the worlds chief food crops.
• Specialty cornssuch as white, waxy, hard
  endosperm food grade, high oil, nutritionally
  enhanced, high amylase and high extractable
  starch cornare being developed.
• Ethanol production from high-starch corn as a
  replacementfor some petroleum fuels has become a
  major use of corn.

48
Grains and Vegetable Crops
Improvement in corn
A primitive type (left ) still growingon the
eastern slope of the Andes mountains in South
America, Modern hybrid corn (right ).
49
Grains and Vegetable Crops

• Rice(Oryza sativa)  

• The basic food for more than half the worlds
  population.
• One of the oldest cultivated cropsbelieved to
  have originated in southeast Asia about 5,000
  years ago, or even earlier.
• There are about twenty-five species, but O.
  perennis, is likely the one from which cultivated
  rice was developed.
• During cultivation, mutations and hybridization
  with other species probably occurred, leading to
  improved forms.
• Rice was first cultivated in America about 1685.
• Experiment stations were established by the U.S.
  in the 1900s, and have resulted in many superior
  cultivars being introduced.
• Hybrid rice is now common in China Southeast
  Asia.
• A genetically engineered rice has been developed
  that produces beta-carotene increasing the
  nutritional value.

50
Grains and Vegetable Crops

• Soybean(Glycine max)

• U.S. soybean production has risen from 5 million
  bushels in 1925 to about 3 billion bushels in
  2008.
• Partly due to more productive, disease-resistant
  cultivars.
• From 1910 to 1950, many new strains seed lots
  were brought to the U.S. from the Orient, largely
  by the USDA.
• Hybridization developed many superior cultivars.
• High yields, proper bean maturity for the
  particular area.
• Strong, erect plants that hold their seeds until
  harvest.
• High disease resistance and bean quality.
• The soybean is particularly well adapted to the
  U.S. Midwest corn belt and the southeastern
  states.
• Which together account for about 40 of the
  worlds soybeans.

51
Grains and Vegetable Crops

• Sugar Beet(Beta vulgaris)

• The modern sugar beet was developed entirely by
  human efforts in plant breedingour only major
  food crop not grown in some primitive form in
  ancient times.
• Developed about 250 years ago in Europe to
  competewith very expensive cane sugar.
• Sugar beets and sugar cane contain the same kind
  of sugar.
• Breeding and selection increased the sugar
  content in the root from about 2 to about 16 -
  20.
• By the end of the nineteenth century, sugar beets
  were being grown in North America.
• They are an important temperate zone crop in many
  areas of the U.S. southern Canadamore so in
  other parts of the world.

52
Grains and Vegetable Crops

• Potato(Solanum tuberosum) 

• One of the big four crops that feed the worlds
  population.
• Wild species are widespread in South America, and
  were likely cultivated in this area more than
  4,000 years ago
• About 1575, Spanish explorers carried it back to
  Europe, where today 90 worlds potatoes are
  grown.
• The potato plant produces pink, white, or blue
  flowersthat develop into small green berries
  containing seeds.
• The seeds produce new types of potato plants much
  different from the parent plant and from each
  other in many respects.
• In early potato culture, the South American
  Indians likely selected superior plant types
  from natural crosses.
• A single superior plant could be perpetuated and
  increasedin great numbers as a clone by tuber
  division.

53
Grains and Vegetable Crops

• Potato(Solanum tuberosum)

• Some superior selections propagated by vegetative
  methods became commercially successful cultivars.
  
• Certain of these cultivars would degenerate after
  many generations yield only weak unproductive
  plants.

• These clonal cultivars had become infected with
  viruses that passed along to generation after
  generation.
• Such viruses do not pass through seed to new
  plantsgrowth is not inhibited by the virus in
  potatoes propogated by seed.
• In modern commercial potato growing, seed tubers
  or seed potatoes are planted to maintain clonal
  uniformity.
• Certified seed potatoes are produced by
  commercial growers and strictly inspected by
  state government agencies.

54
Grains and Vegetable Crops

• Tomato(Lycopersicon esculentum)

• The cultivated tomato originated from wild forms
  in the PeruEcuadorBolivia area of the Andes
  Mountains.
• Explorers introduced the tomato to Europe about
  1550.
• It was brought back west, to the Carolinas, about
  1710.
• Most people considered the tomato poisonous.
• U.S. acceptance of it as a food plant began about
  1825.
• In the early 1900s, USDA state experiment
  stations began breeding cultivars to include
  specific characteristics.
• Recently introduced cultivars are resistant to
  fusarium wilt, verticillium wilt, and
  nematodesthose developed for machine harvesting
  have firm-fleshed fruits that all ripen at one
  time
• Vigorous, highly productive F1 hybrids, marketed
  both as seeds bedding plants, are recent
  developments by seed companies.

55
Grains and Vegetable Crops

• Apple(Malus pumila) 

• Early colonists likely planted many seedlings
  because it was easier to bring seeds rather than
  material for grafting.
• They continued to increase their orchards by
  planting seedlings.
• Certain individual seedling trees were much
  superior to the others formed the starting
  point for many hundreds of cultivars grown in the
  U.S.
• These numbers dwindled until the 1980s, when 15
  cultivars accounted for over 90 of the apples
  produced in the U.S.
• All the major apple cultivars now being grown
  originated as chance seedlings many years ago.
• The McIntosh apple was found growing as a
  seedling treenear Dundela, Ontario, Canada by
  John McIntosh in 1796.
• The Delicious started as a chance seedling near
  Peru, Iowa.

56
Grains and Vegetable Crops

• Pear (Pyrus communis)  

• Cultivars originating as chance seedlings have
  dominated.
• Te Bartlett originated in England as a chance
  seedling in 1796.
• No pear cultivar from a controlled breeding
  program inthe United States has become
  commercially important.

57
Fruit Crops

• Peach and Nectarine(Prunis persica)  
• Important peach and nectarine cultivars grown
  today are the products of public private plant
  breeding programs.

58
Fruit Crops

• Strawberry(Fragaria x Ananassa)

• Todays strawberry originated in France about
  1720 as a natural hybrid between two American
  Fragaria species.
• A number of cultivar selections were made and
  maintained vegetatively by runners in the early
  days of strawberry culture.
• Early cultivars were susceptible to viruses,
  verticillium wilt, and other diseases and were
  low in productivity.
• Since World War II, many new cultivars have
  replaced older ones, from USDA state breeding
  programs.
• New cultivars have been developed for
• Specific climatic regions.
• Adaptability of fruits to for freezing or for
  fresh shipping.
• Resistance to viruses, fungi and to winter cold.
• Fruit appearance flavor, and extended
  fruit-producing period.

59
Evolution and Darwinism

• Charles Darwin provided scientific
  explanationsof how evolution occurred, published
  in 1859.
• In Darwins time, nothing was known about
  heredity.

• Gregor Mendel, in the 1860s, demonstrated the
  genetic mode of plant inheritance.
• The foundation for the science of genetics.
• Integration of Darwinian selection and Mendelian
  genetics are now generally accepted as the proper
  explanation of evolution.
• Many crop scientists have discovered patterns of
  evolution in various crop genera.
• Breeders have made useful application of this
  knowledge in terms of collecting utilizing
  germplasm resources

60
Evolution and Darwinism

• Modern breeding programs have produced an array
  of new cultivars for many cropsin what has been
  called directed and accelerated evolution.

• Since the start of the 20th century, breeding
  programs have had a tremendous beneficial impact
  on our food supply and range of ornamental
  plants.
• The USDA most state agricultural experiment
  stationsin the United States maintain such
  programs.
• Most new vegetable flower lines are far
  superiorin vigor and insect disease
  resistance.
• New vegetable cultivars are also superior in
  flavor, appearance, and productivity.

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Evolution and Darwinism

• By developing plants that show strong resistance
  to insects and disease, plant breeders are
  reducingthe need for insecticides and
  fungicides.

• Plant breeders have a useful procedure for
  obtaining improved plant forms by spontaneous or
  induced mutations from chromosome or gene
  changes.
• Induced by chemical treatment with colchicine or
  by irradiation with gamma or X-rays.
• Breeders created a new human-made cereal,
  triticale, by hybridizing, wheat and rye.
• The name triticale derives from the generic names
  of these two grains Tritium and Secale.

62
Evolution and Darwinism

• Germplasm is the protoplasm of reproductive cells
  containing the units of heredity.
• Chromosomes genes.

• Plant explorers continue their searches for
  germplasm containing useful genes.
• They have found many plants that have
  subsequently made a major impact on the worlds
  agriculture.
• Plants moved into a new region often perform much
  better than they did in their original home.

63
Evolution and Darwinism

• Many early plant collecting trips were
  unsuccessful because the plants did not survive
  the long trip back.

• Nathanial Ward, invented the Wardian caseasmall
  glass-enclosed box with soil in the bottom.
• Plants in a Wardian case could survive long sea
  voyages, allowing importation of species never
  before received alive.
• Many plant explorers from the U.S. brought back
  plants that would be the foundation for several
  crops.
• Plant-collecting trips to the native homes of
  certain desirable plant types are still being
  made.

64
Evolution and Darwinism

• Two international conventions relate to
  promotionof conservation protection of
  biological diversity.
• The Convention on International Trade in
  Endangered Species of Wild Fauna and Flora
  (CITES).
• The Convention on Biological Diversity (CBD).

• Annually, an estimated 500 - 800 billion of
  genetic resources derived products is traded
  globally.
• Moving plant materials about the world can
  introduce devastating insect or disease pests
  into a country where they have never before
  appeared.
• To guard against the introduction of such pests,
  most countries have set up elaborate inspection,
  fumigation, and quarantine procedures.

65
Evolution and Darwinism

• A concerted worldwide effort is needed to ensure
  the survival of the earths endangered plant
  species and thus preserve genetic diversity.
• In 1998, FAO estimated that 6.1 million
  accessions of food, forage industrial crops had
  been conserved.

• Genetic diversity of plants, animals and
  microbes,is of fundamental importance to our
  survival.
• Food and other agricultural crops are derived
  from the genetic diversity of natural plant
  populations.
• As many as one in ten plant species is now
  extinct or endangered.
• Such endangered germplasm can be saved stored
  for future use as seeds or living plants in
  protected locations.

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Broadening the Base of Agricultural Production

• The worlds peoples are largely fed today by only
  about twenty crops.
• Reliance on so few crops could lead to a
  catastrophic famine if but a few of them were
  obliterated by insector disease attacks or by
  climatic changes.

• Since 1990, crop scientists have met regularly in
  the United States to share information on new
  crops and the potential for new crop development.
  
• Looking for solutions to problems like hunger,
  malnutrition, deforestation, desertization, and
  agricultural sustainability.

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