Plant Breeding

this unit of study deals with plant breeding this unit will cover the basic principles and understanding of plant inheritance Mendelian genetics and plant breeding methods used to improve crop varieties plant breeding is the art and science of improving genetically controlled traits of plants for human benefit it began thousands of years ago when humans first observed differences in plant growth and began to collect and store seeds for planting next year's crop until the last century plant breeding mainly relied on the art of identifying and selecting superior types based on skill judgment and luck often this important task was the responsibility of women in the ancestral farming communities as the scientific fields such as botany genetics chemistry and mathematics progressed in the last century so did the science of plant breeding an Augustine monk Gregor Mendel working with garden peas published a landmark paper in 1866 which explained the basic mechanisms of plant inheritance through advances in scientific knowledge since Mendel's time plant breeders became able to design and create new more effective breeding methods to improve crop species the modern plant breeder takes a lot of credit for the advances in crop production we should not forget however that primitive agriculturalists selected crops for centuries before more modern scientists began developing the art and science of plant breeding one should realize that successful plant breeding improves the genetic potential for optimum growth of crop plants the inheritability of crop plants to produce will be greatly influenced by the production environment such as moisture soil characteristics fertility and pests to maximize genetic performance of improved crop varieties the proper production practices must be used the next topic for study is the section on plant inheritance you should now stop the VCR and study this section in your text then return to the VCR for further tutoring the phenotype of a plant is the appearance and/or performance of the plant in other words it's what we see or observe in the plant most of us have probably noticed large variation in the way plants grow and develop even for plants that are closely related to each other this phenotypic variability is caused by genetic and environmental variability for the usable portion for plant breeders is the genetic variability because this portion is heritable by selecting superior plant traits that are under genetic control the desired traits can be passed on to the progeny if you selected a desired phenotype that was due to environment the progeny may not be light the selected parent because environmental changes are not heritable and differ from day to day in year to year in this case selection for superior traits would not be successful each of the thousands of traits that make up the individual are controlled by genes genes are the basic unit of heritance that are passed on to new generations all of the genes of an individual are contained in the chromosomes chromosomes are actually strands of DNA which are composed of proteins and nucleic acids in encoded form that contain the complete assembly and operational instructions for the cell genes are segments of DNA strands that code for a specific trait there are hundreds of genes on each chromosome and each cell contains many chromosomes the actual number of chromosomes among cells within a plant or species is constant but the number will vary among crop species for example each normal cell in a maize plant has 20 chromosomes barley cells contain 14 chromosomes while wheat cells contain 42 chromosomes the entire genetic blueprint of the cell or individual is found in these chromosomes and the genes they contain thus the chromosomes of an individual contain all the genetic information of thousands of genes and the multitude of traits they control in most crop species there are two complete sets of chromosomes in each normal cell nucleus one set coming from each parent for example maize has a total of 20 chromosomes or two complete sets of 10 chromosomes each therefore each chromosome has a homolog or in other words another chromosome that is structurally similar to it each homolog carries the same genes at the same location in the same order these similar pairs of chromosomes are called homologous chromosomes plants or cells that contain two sets of all chromosomes are referred to as diploid and are designated 2n reproductive cells such as egg or sperm cells have only one set of all chromosomes reproductive cells are referred to as haploid and are designated one in thus a normal leaf cell of maize would be 2n contained two complete sets of 10 chromosomes each in a total of 20 chromosomes an egg cell of maize would be one an contained one complete set of 10 chromosomes for a total of 10 chromosomes the term genome is used to describe a complete set of chromosomes all diploid cells contain two genomes for example in a maize diploid cell both genomes consist of 10 different chromosomes for a total of 20 chromosomes a single chromosome contains many genes the location or place that the gene occupies on the chromosome is called the locus Llosa refers to the locations of several genes because there are homologous chromosomes in the nucleus of a diploid cell there are two copies of each gene or a gene pair for each trait at a particular locus each gene can have different forms of expression called alleles for example a gene controlling flower color can have an allele for red flowers another allele for blue flowers and another for yellow flowers and so on thus a gene may have many alleles but an individual plant has only one pair some alleles are dominant over other recessive alleles dominant alleles express themselves with or without the presence of a recessive allele recessive alleles are masked in the presence of a dominant allele and are only expressed when the gene pair has both identical recessive alleles this can be illustrated using an imaginary pair of homologous chromosomes the one on the left came from the female parent and the one on the right from the male parent suppose the gene for flower color is located at the locus designated l15 the allele for blue flowers is present on the left chromosome it is a dominant allele so it is designated with a capital B the allele for white flowers is present on the right chromosome it is a recessive allele so it is designated with a lowercase B the gene pair for flower color for this individual plant would be Big B little B the presence of the dominant allele in the gene pair would produce a plant with blue flowers the terms homozygous and heterozygous refer to the type of alleles present for the gene pair homozygous dominant means the gene pair has identical dominant alleles or in this example Big B Big B homozygous recessive means the gene pair would have identical recessive alleles little B little B in this case and the plant would have white flowers gene pairs that have different alleles such as Big B little B in this example would be termed heterozygous which implies that the dominant allele would be expressed for that trait in this example blue flowers a plant is made up of billions of cells that originated from an original zygote or fertilized egg cell these cells are called somatic cells and contained the normal chromosome number of the species the entire chromosome complement for the individual is contained in each cell and must be duplicated and passed on to each newly formed cell this is accomplished through mitosis mitosis is the process of cell reproduction where the cell nucleus is divided into two nuclei each having an identical chromosome complement this process of genetic duplication occurs billions of times during the life of a plant and since each cell is replicated from a previous one all of the plant cells will contain the same chromosome complement gametes or reproductive cells such as egg and sperm cells are formed from meiosis during the sexual reproduction process in crop plants meiosis is a process of cell division where the normal diploid number of chromosomes is reduced in half gametes therefore are haploid or 1n and have one complete set of chromosomes instead of the normal two complete sets of chromosomes found in diploid somatic cells the formation of haploid gametes through meiosis is extremely important because upon fertilization of the egg and sperm the normal diploid number of chromosomes is restored in the zygote without meiosis chromosome numbers would keep doubling with each new generation and be lethal to the plant most crop plants are sexually reproduced meaning that male and female gametes are formed and United with each other during fertilization this union produces a new individual zygote cell which then multiplies and develops into the seed sexual reproduction can be divided into three steps yeah metal Genesis pollination and fertilization during gametogenesis the stamen and pistol which are male and female reproductive organs of the flower produced male and female gametes from meiosis and mitosis the diploid microspore mother cell in the stamen mitotic li divides producing four haploid microspores the microspore matures and the nucleus mitotically divides producing a pollen grain with two haploid nuclei one nucleus in the pollen grain is called the generative nucleus and the other is called the tube nucleolus the pollen grain is now mature and ready for transport the diploid megaspore mother cell is developed in the ovary of the flower it mitotic Li divides producing four haploid megaspores three of which disintegrate the surviving megaspore matures and the nucleus undergoes three mitotic divisions resulting in an oval with eight identical nuclei contained within the embryo sac the two nuclei in the center are called polar nuclei and the bottom center nucleus is the egg cell the mature oval is now ready for fertilization pollination is the transfer of pollen from the anther to the stigma of the flower pollination may be accomplished by wind and wind pollinated crops by bees or other insects in insect pollinated crops or simply by gravity where pollen from the anther falls on the stigma within the same flower in self pollinated crops when pollen lands on the stigma the process of fertilization begins the tube nucleus in the pollen grain begins to digest a pathway or tube through the style into the base of the ovary at the same time the generative nucleus undergoes another mitotic division forming two identical sperm nuclei which travel through the tube and enter the ovary one sperm nucleus unites with the egg cell to form the diploid zygote cell which continues to develop into the mature embryo of the seed the other sperm cell unites with a two polar nuclei to form the endosperm cell this is called triple fusion in this process three haploid nuclei are fused together to form a triploid 3 in endosperm cell the endosperm cell continues to mitotically divide producing more endosperm cells each having three sets of chromosomes or genomes two from the maternal parent and one from the paternal parent the fertilization process in seed formation is called double fertilization one fertilization is the union of the sperm and egg nuclei to form the embryo the other fertilization is the union of the second sperm and the two polar nuclei to form the endosperm in seeds of some species such as grasses the major portion of the seed is triploid endosperm tissue in seeds of other species such as legumes the endosperm does not develop to a great extent so most of the seed is made up of 2n or diploid embryo tissue one of the great advantages of sexual reproduction in crop plants is the separation and recombination of allelic pairs a simple cross involving one trait can be used to illustrate this the genotype for the female parent on the left is big t little T and for the male parent on the right big t little T through gametogenesis or gamete formation the alleles of the gene pair separate into haploid gametes the possible genotypes of the female a are either big t or little T the possible genotypes of the male sperm are also big t or little T during fertilization the random union of male and female gametes can give rise to different genetic combinations of new individuals the offspring may be big t big t big t little T or little T little T through sexual reproduction alleles were isolated and segregated into gametes and recombined into new combinations of alleles during fertilization this process can provide new genetic variation from which plant breeders can select superior genotypes to understand the breeding strategies and the difference between self and cross pollinated crops it's important to understand the effects of selfing or inbreeding over time on the segregation and recombination of alleles using the same letter T as used in the previous example let's assume that the trait is plant height big T is dominant for tall plants and little T is recessive for short plants the first cross is a hybrid cross between genetically different parents the female parent on the Left is homozygous dominant for tallness or big t big t and the male parent on the right is homozygous recessive for shortness or little T little T all of the f1 or first-generation plants in this cross would be heterozygous dominant or big t little T and would be tall all plants in the population would be identical and therefore the population is homogeneous note there would be no variation or segregation of different genotypes in the f1 population to generate the f2 population all f1 plants would be self pollinated thus the genotypes of both the f1 female and the f1 male would be big t little T the f2 progeny would segregate into a one to one ratio 25% or one quarter of the f2 plants would be homozygous dominant or big t big t and tall 50% or 1/2 would be heterozygous dominant big t little T and tall and 25% or 1/4 would be homozygous recessive little T little T and thus short the f2 population has segregated into a mixture of plants with different genotypes therefore the population is heterogeneous note that by selfing the hetero zygosity of the population was decreased from 100% in the f1 to 50% in the f2 at the same time homozygosity was increased by 50% and divided equally between homozygous dominant and homozygous recessive individuals this pattern of reducing hetero zygosity by 1/2 and increasing homozygosity by 1/2 occurs every time the generation is selfed thus the f3 would have 25% or 1/4 heterozygous dominant tall plants 37 and a half percent or 3/8 homozygous dominant tall plants and 37 and a half percent or three-eighths homozygous recessive short plants the f4 generation would have 12 and a half percent or 1/8 heterozygous dominant tall plants 43 and 3/4 percent or 7/16 homozygous dominant tall plants and 43 and three quarter percent or 7/16 homozygous recessive short plants it becomes evident that after several generations of selfing essentially all of the plants would become either homozygous tall or homozygous short very few individuals in the population would still be heterozygous once homozygous 80 is reached the trait will breed true in succeeding generations as long as the plant continues to be self pollinated the next topic for study is the section on improving crops through plant breeding you should now stop the VCR and study this section in your text then return to the VCR for further tutoring plant breeders have many different goals or objectives in their efforts to improve crops some concentrate on yield improvement or pest resistance others may try to improve the plant's ability to hold seed during harvest time or to improve stock strength some may try to improve the quality of the seed for better food value or for industrial uses plant breeders use a variety of breeding methods to achieve their crop improvement goals they can be categorized into three general methods introduction selection and hybridization these methods are used to accomplish two distinct and important steps in plant breeding these steps are find or expose genetic variability and then select desirable traits within that genetic variability for the type of plant or line that you want to produce introduction and hybridization are ways of exposing genetic variability and selection is a method of identifying and putting desirable genetic variability to proper use the introduction method means simply bringing in a new collection of plants from one area to another these new plants could be directly used as varieties introduction is often used in the early stages of the breeding program frequently additional breeding methods are later years to refine or improve the traits of the original introduction introduction is also an excellent way to introduce new genetic variability and diversity in the germ plasm available for a given crop in a given production area it's been widely used on most major crops of the world since humans first began saving seed to take with them as they move to new areas selection is another general breeding method and can be divided into mass or pure line selection mass selection is frequently the next step after introduction in mass selection a group of plants having the same desired traits are selected the seed composited or mixed together and the mixture used as next year's variety farmers throughout the world have used this form of selection to continue improving crop performance in the early part of this century farmers in the United States would pick corn by hand and save the superior ears in a special seed box these superior looking ears would be the source of seed for next year's crop the practice most likely learned from the Native American Indians this was an example of mass selection pure line selection involves selecting individual homozygous plants and growing the progenies of each selected plant the progeny of a homozygous plant is known as a pure line homozygous plants have traits where the gene pair has identical alleles such as the big t big t for the hypothetical trait big t if both parents are homozygous big t big t then the progeny and succeeding generations will also be big t big t the progeny will be pure line and breed true because the same genotype will be carried from generation to generation this pure line could become a variety if it is superior in performance to the older varieties this breeding method is widely used for self pollinating crops like barley oats and soybeans it's also used as an important part of broader breeding programs for many other crops including cross pollinated crops it's important to remember that for selection to be successful plants within a population must be of different genotypes the difference between mass selection and pure line selection is also important the result from mass selection would be a mixture of similar plants that may differ for some characteristics the result from pure line selection would be a group of identical plants hybridization is the third general breeding method and is the mating of genetically different individuals this can be accomplished by artificially transferring the pollen of the desirable male parent to the stigma of the desirable female parent in self pollinating crop species that have both male and female parts within the same flower the stamens must be removed before crossing to avoid self-pollination hybridization of existing varieties lines or plants allowing recombination of alleles and genes or different traits in the offspring is a way to expose genetic variability selection would be the next step after hybridization to identify and select the desirable genotypes hybridization can be used for different purposes it can be used to recombine alleles and improve a single character such as yield or it may be used to recombine two or more desirable characteristics of the parents into one individual such as yield and lodging resistance hybridization can also be used to produce an f1 hybrid that expresses heterosis or hybrid vigor over that of the parents this is often used in maize breeding to improve maize varieties to illustrate hybrid vigor suppose high yield actually was caused by the presence of dominant alleles at four low side by crossing parent one that had high yield genes at low sigh one and two with parent two that had high yield genes at low sigh three and four we would be able to produce an f1 hybrid that had one dominant allele for each of the four loose I giving extremely high yield therefore the f1 hybrid progeny expresses heterosis over that of its parents improving crop varieties through plant breeding is challenging and difficult because many characters are controlled by more than a single gene frequently desirable traits of agronomic importance are conditioned by alleles at many low sai traits such as high yield and drought tolerance may be controlled by many genes some of which are not known to the plant breeder the next topic for study is the section on breeding methods used in self and cross pollinated species you should now stop the VCR and study this section in your text then return to the VCR for further tutoring knowing whether a crop species is normally sell for cross pollinated is essential to plant breeders the type of pollination will influence the genetic characteristics of the population and the method of breeding used to improve the crop species like soybeans and oats are self pollinated and therefore naturally produce homozygous genotypes homozygous genotypes breed true from generation to generation therefore the goal in breeding is to select superior genotypes develop homozygosity in the population and release the resulting pure line as a new variety cross pollinated crops like alfalfa and sunflowers naturally produce heterozygous genotypes when an insect pollination contribute to a random mating of parents random mating gives rise to many different gene combinations and mixing of alleles for example pollen from a male parent carried by a bee may be deposited on the stigma of a female flower located in another field or from another variety of the same crop species therefore the resulting population from cross pollination changes in each succeeding generation and will not breed true from generation to generation undesirable recessive alleles may be present at different low sign but may be masked by desirable dominant alleles the breeding goal for cross pollinated crops therefore is to select plants that when cross pollinated produce desirable progeny performance the breeding methods used for self pollinated crops usually begin with a hybridization of two homozygous but unrelated pure lines hybridization is used to recombine genes and create variability then selection of desirable plants is made in the F2 or later generations selection is not made in the F1 because the population is not segregating and all F1 progeny have the same genotype remember that as each generation is formed by selfing the genes will move toward a homozygous state and the selected plants for a new variety eventually will breed true based on these concepts four common breeding methods are used to create new varieties for self pollinated crops the pedigree method of selection begins with an initial hybridization step to recombine desirable genes of two unrelated lines selection begins in the F2 generation when plants are selected the seed is saved and used to plant a row of plants for the next generation of selection this continues in each succeeding generation through the F6 generation the remaining plants that survive this selection procedure and are good candidates for possible new varieties are subjected to yield trials to determine their yielding ability the highest yielding selections are then identified and the seed supply increased for cultivar release by this time the selected plants have gone through 11 or more generations of selfing and will be homozygous pure lines that will breed true each line developed this way has a definite pedigree which can be traced back to the originally selected F2 plant this method is often used for readily observable traits but requires a lot of hand labor and expense because selection begins early in the breeding program the bulk method of selection is similar to the pedigree method of selection except that selection begins in the F6 generation prior to the F6 all plants in the generation are harvested in bulk and a representative sample of seeds is used to plant the next generation after F6 yield trials and seed supply increased steps are conducted in the same fashion as the pedigree method because selection does not begin until the F6 labor and expense is lower for the bulk method of selection the single seed descent method of selection is similar to the bulk method of selection except that a single seed from each plant in the generation is saved and grown to produce the next generation this is in contrast to the bulk method where all seed is harvested in bulk and a sample is used to plant the next generation like the bulk method selection begins in the F6 and yield trials and seed supply increase follow this method is especially useful to speed up the in breeding process because the plant only needs to produce one seed small plants can be grown in the greenhouse or growth chamber in this manner two or more generations can be grown per year greatly decreasing the amount of time necessary to develop and release new varieties the fourth method of breeding used in self pollinated crops is the back cross method of hybridization it is used to transfer desirable genes from a donor parent into an existing good variety this method allows a breeder to improve an existing variety that is weak in one or more characteristics while maintaining its desirable characteristics the initial step like the previous methods is hybridization the donor parent is crossed with the existing variety to allow the superior genes to move into the F1 progeny then the F1 progeny is made it back to the existing variety this is called back crossing the progeny from this cross is called the BC-1 meaning the first back cross progeny desirable plants in the BC-1 generation are identified and again back crossed with the existing variety this procedure continues until the fourth back cross progeny is obtained in this breeding scheme the existing variety is called the recurrent parent because each generation from the F1 to the BC4 is back crossed to the original existing variety the donor parent is only used once in the initial hybridization cross the next step is to select the desirable plants in the BC4 progeny and allow them to self pollinate this step will allow the population to segregate enabling the plant breeder to select plants that are homozygous for the desired traits these plants will breed true for succeeding generations and can be used as new varieties this method is widely used to transfer desirable genes of another plant or line such as disease resistance into an established variety by back crossing to the recurrent parent and using proper selection procedures the new variety will be nearly identical to the original variety but will have the new desirable genes in cross pollinated species the random mating of parents results in populations with heterozygous genotypes therefore varieties will not breed true from generation to generation breeding methods are used to identify and develop parental lines that when cross pollinated will produce superior progeny two major methods are used to accomplish this producing F1 hybrid crosses and developing synthetic varieties producing F1 hybrid crosses is used on crops such as maize in which cross-pollination can be controlled on an economic and commercial scale and where the F1 hybrid expresses heterosis over its parents one of the first steps in producing an F1 hybrid variety is to produce homozygous inbred lines these inbred lines are produced essentially by the same methods used to produce varieties of self pollinated crops except that control self pollination is necessary in cross pollinated crops inbreds used as parents to produce the F1 hybrid are selected for superior agronomic traits and the ability to produce superior progeny exhibiting hybrid vigor or heterosis once the female and male inbred parents have been selected for the hybrid cross commercial scale seed production is undertaken in hybrid maize seed production fields female inbred parents are grown in rows adjacent to the male inbred pollinator rows female inbred plants because they also form tassels must be detested to prevent self pollination and to ensure pollination from the desired male inbred female plants can be detasseled by hand, by machine or by combinations of both because the maize plant produces male flowers in the tassel at the top of the plant away from the female flowers located in the ear chute it's feasible to detassel female plants on a commercial scale to force the desired female male inbred cross the seed produced on the female plants is the F1 hybrid cross it is carefully harvested cleaned sorted bagged and sold to farmers when the F1 hybrid is a cross between two homozygous inbred lines the hybrid seed sold to farmers is called single cross seed single cross seed has identical genotypes and will be homogeneous and uniform in the farmers fields farmers do not save seed for next year's planning because the plants would self pollinate forming an F2 generation that segregates in the undesirable genotypes genetic male sterility is used to make commercial scale hybridization possible for many crops where hand or machine removal of the male flowers is not feasible for example many cereal grains have both male and female parts located within the same flower thus self pollination is possible and likely genetically male sterile plants produce flowers that have sterile pollen preventing self pollination of the same flower or another flower on the same plant hybrid grain sorghum for example is produced using genetic male sterility the female inbred plants are genetically male sterile forcing hybridization with the male fertile inbred plants the other breeding method developing synthetic varieties is used when controlling cross-pollination to produce F1 hybrids is not feasible economically or commercially this may be due to insect pollination, the lack of suitable male sterility mechanisms, severe inbreeding depression when making inbreds for hybrid crosses or other factors because pollination cannot be controlled to produce F1 hybrid varieties the objective of producing synthetic varieties is to select agronomically superior parents that when open pollinated or randomly cross pollinated with each other produce superior progeny the initial step is to select 200 to 400 superior plants from a source nursery that contains thousands of different plants vegetative cuttings are made from the selected plants to produce rows of identical plants called clones the rows of cloned plants are further evaluated and the selection of desired plants is narrowed the selected lines are clonally reproduced in another location and allowed to randomly pollinate each other followed by a progeny test this is called a poly cross test and is used to test the combining ability combining ability refers to the ability of lines to produce superior progeny when randomly cross pollinated with each other based on the poly cross test the selected clones are narrowed to as few as four or as many as 50 which will be used in the new synthetic variety the remaining step is to produce enough seed for varietal release the selected clones are planted together in a new location and allowed to randomly cross pollinate with each other the seed is harvested cleaned and bagged for varietal release a synthetic variety therefore is really a mixture of seeds from clones that have superior agronomic traits and produce superior progeny when randomly cross pollinated with each other this breeding approach helps ensure that the seed of a synthetic variety will germinate and grow into a healthy productive property heterozygosity remains in a synthetic variety because of continued cross-pollination in seed production fields because each plant is a hybrid that is the progeny of cross-pollination in the field a synthetic variety makes use of a limited amount of heterosis or hybrid vigor the next topic for study is the section on cellular and molecular genetics you should now stop the VCR and study this section in your text then return to the VCR for further tutoring most major crops pass on genetic information from generation to generation by sexual reproduction seeds produced from this sexual union between male and female parents represent the genetic package for the new individual offspring however the genetic exchange through sexual reproduction and seed formation normally occurs only among closely related plants within a species this is due to sexual incompatibility among plants across a species that prevents successful pollination or fertilization or results in aborted embryos sterility or lethal aberrations in the offspring therefore a desirable trait found in wheat cannot be transferred to maize barley or green sorghum to overcome the limitation of sexual incompatibility among species for genetic exchange techniques in cellular and molecular genetics are being developed three general tools being used to transfer genetic information at the cellular and molecular levels are plant cell and tissue culture, somatic cell hybridization and genetic engineering plant cell and tissue culture refers to the use of plant cells or tissues to regenerate a new plant this method shortens the generation time because seed formation is not required the genetic material can be passed on to a new plant from the genetic contents of the cell or tissue used to regenerate the new plant some species have self sterility preventing seed formation when self pollination occurs within the flower therefore plant cell and tissue culture can be used to avoid problems of self sterility and loss of seed formation among certain crop species somatic cell hybridization refers to the fusion of cell protoplasts from normal diploid or somatic cells that are genetically different from each other whole plants are then cultured and grown from the fused cells thus new genetically different plants may be developed without the normal requirements and limitations of pollination, fertilization and seed formation genetic engineering refers to the identification, isolation, duplication and insertion of genes or pieces of DNA from the chromosomes of one individual into another genetic engineering is also referred to as gene transfer or gene splicing and recombinant DNA technology by identifying the genes or sections of DNA that determine the desirable trait and transferring them directly into the appropriate section of the chromosome of another species the limitation of sexual incompatibility among species can be avoided thus genetic exchange of desirable traits may be possible over a wide range of plant species the last topic for study is the section on concerns and considerations in molecular genetics and plant breeding you should now stop the VCR and study this section in your text then return to the VCR for further tutoring genetic diversity among plant species is a valuable resource a wealth of genetic information can be found in the diverse array of inherited traits contained in genomes of thousands of plant species evolving over thousands of years this genetic information is a story of the past and the potential for the future modern agriculture and plant breeding efforts have primarily focused on a narrow range of plant species less than 20 species provide most of the world's food supply furthermore of the popular crop species much of the genetic improvement has been developed from a narrow and similar genetic base thus the world's food supply depends upon a relatively small amount of the genetic base contained in the plant kingdom it is essential that we preserve the living hereditary properties of plant organisms Germplasm refers to the hereditary properties of an organism collecting and preserving the germ plasm of plants in the form of seeds is a means of preserving genetic diversity plant breeders and governments have undertaken efforts to collect and preserve germ plasm of many crop species even so many wild species and historical races of cultivated crop species have become extinct or are reaching extinction from agriculture and industrial practices extinction of a plant species also implies extinction of the valuable genetic information contained within that species a resource that is non recoverable much understanding and world support is needed to maintain and expand our germ plasm collection of plant species for the benefit of humankind advances in genetic engineering and plant breeding have increased the concern for intellectual property rights the trend in plant breeding programs and genetic engineering laboratories throughout the United States has been to patent new varieties molecular breeding techniques and genes that have been identified and isolated by advanced techniques these scientific discoveries are referred to as intellectual discoveries and can be patented under the concept of intellectual property rights to protect the investment rights of the owner patenting encourages the financial investment in the high cost of plant breeding and molecular genetic research which in turn results in newer and better varieties however there is also concern that patenting intellectual discoveries in plant breeding and genetic engineering may hinder germ plasm exchange among public and private institutions and among developed and developing countries plant breeding and molecular genetics our tools used to improve plants for human use plant breeding is an art and a science that has been evolving since farmers first began collecting seeds for next year's crop goals and challenges for breeding programs change as agricultural and societal needs change these goals should reflect not only economic benefits but also environmental and humanistic goals of our world society therein may lie the biggest challenge in plant breeding efforts this is the end of the chapter on plant breeding you should now be ready to try the self evaluation test at the end of the chapter in your text (upbeat music)