hybrid varieties are produced by manual pollination, as for example in tomato. In anumber of crops cytoplasmic male sterility is being sought with a view to theeconomic production of hybrid varieties. Purely genic male sterility is difficult tohandle on a large scale.Diallel AnalysesDiallel analyses in self-pollinated species are little used inapplied breeding. They are an important adjunct to breeding, allowing the analysis ofgeneral and specific combining ability, but their predictive value is uncertain as theprocedure has so many prerequisites that it can hardly be applied to breeding material.Moreover in many species a full diallel analysis is very laborious.MultilinesThe possibility of using multilines, i. e mixtures of nearlyisogenic lines, in autogamous crops has attracted the attention of many plant breedersinrecent years.To prevent an epidemic spread of air-borne diseases such as rust inwheat, the cultivation of multiline mixtures in which the lines differ only in theirresistance to different races of the pathogen is sometimes advocated. An importantdrawback in breeding multilines is that many repeated back crosses of an existingoutstanding variety to several resistance sources are required.This is atime-consuming process and has the result that by the time the multiline is introducedit is already outyielded by newly bred conventional varieties.Mixtures of varieties, similar in agronomic properties such as earliness, height,grainsize etc. but differing in race-specific resistance, can serve the same purposeas the multiline, but here the difficulty of achieving agricultural uniformity is moreserious. In this respect, mixtures of sister lines from "multiple crosses (involvingmore than two parents) may be expected to have certain advantages, since they are, ormay be, related in several traits and since they have a broader spectrum of resistancethan two-parent lines.MultipleCrossesWhereit is desired to combine more than twodistinctcharacterswhich are only available inmorethan two parents, wheat breeders inparticular are turning to the use of multiple crosses. Some breeders, however, are notaware that the frequency of favourable alleles in an F × Fi cross is considerablylower than in a conventional F2 generation.The same is true of the succeeding16
16 hybrid varieties are produced by manual pollination, as for example in tomato. In a number of crops cytoplasmic male sterility is being sought with a view to the economic production of hybrid varieties. Purely genic male sterility is difficult to handle on a large scale. Diallel Analyses Diallel analyses in self-pollinated species are little used in applied breeding. They are an important adjunct to breeding, allowing the analysis of general and specific combining ability, but their predictive value is uncertain as the procedure has so many prerequisites that it can hardly be applied to breeding material. Moreover in many species a full diallel analysis is very laborious. Multilines The possibility of using multilines, i. e mixtures of nearly isogenic lines, in autogamous crops has attracted the attention of many plant breeders in recent years. To prevent an epidemic spread of air-borne diseases such as rust in wheat, the cultivation of multiline mixtures in which the lines differ only in their resistance to different races of the pathogen is sometimes advocated. An important drawback in breeding multilines is that many repeated back crosses of an existing outstanding variety to several resistance sources are required. This is a time-consuming process and has the result that by the time the multiline is introduced it is already outyielded by newly bred conventional varieties. Mixtures of varieties, similar in agronomic properties such as earliness, height, grain size etc. but differing in race-specific resistance, can serve the same purpose as the multiline, but here the difficulty of achieving agricultural uniformity is more serious. In this respect, mixtures of sister lines from "multiple crosses (involving more than two parents) may be expected to have certain advantages, since they are, or may be, related in several traits and since they have a broader spectrum of resistance than two-parent lines. Multiple Crosses Where it is desired to combine more than two distinct characters which are only available in more than two parents, wheat breeders in particular are turning to the use of multiple crosses. Some breeders, however, are not aware that the frequency of favourable alleles in an F1 F1 cross is considerably lower than in a conventional F2 generation. The same is true of the succeeding
generations.For this reason multiple crosses cannot be used for combinations ofmorethan approximately ten favourable alleleswithout risking the loss of a largeproportion of them.3. Allogamous CropsAs in autogamous crops, selection in allogamous crops started with massselection, followed by such improvements as half-sib family selection and full-sibfamily selection.Mass SelectionIn its simplest form,mass selection is now practised onlyincrops of minor economic importance or in crops that have undergone little breeding.Its use is justifiable only for characteristics with highheritability and even then it isnot very efficient, especially if the alleles to be eliminated are present in lowfrequencies. Mass selection after flowering is even less efficient than mass selectionbefore flowering.Half-sib Family SelectionThis method involves an evaluation of theprogeny from each mother plant. As each mother plant has been fertilized by morethan one father plant, it may be said that the mother plants have been open pollinated.Since the half-sibs often flower simultaneously, separating them from each other canbe a costly procedure and is rarely worthwhile.For this reason the method is morefrequently applied to crops that can be selected before flowering than to seed crops.Generally speaking, it may be said that half-sib selection is based on generalcombining ability, the entire population being used as a tester.A variant of the half-sib selection procedure is the polycross method. Thepolycross is particularly suitablefor cross-pollinated crops which can be propagatedand maintained vegetatively for purposes of breeding (e.g. many grasses and somelegumes) .This procedure and its many variants have been used to develop a greatnumberofsynthetics.Full-sibFamilySelectionHere selection is carried out in the progeny of amother plant which has been pollinated by only one father plant. Continued full-sibfamily selection leads to a rapid narrowing of the population. In effect, full-sib familyselection is a test for specific combining ability. It is an effective means of selecting17
17 generations. For this reason multiple crosses cannot be used for combinations of more than approximately ten favourable alleles without risking the loss of a large proportion of them. 3. Allogamous Crops As in autogamous crops, selection in allogamous crops started with mass selection, followed by such improvements as half-sib family selection and full-sib family selection. Mass Selection In its simplest form, mass selection is now practised only in crops of minor economic importance or in crops that have undergone little breeding. Its use is justifiable only for characteristics with high heritability and even then it is not very efficient, especially if the alleles to be eliminated are present in low frequencies. Mass selection after flowering is even less efficient than mass selection before flowering. Half-sib Family Selection This method involves an evaluation of the progeny from each mother plant. As each mother plant has been fertilized by more than one father plant, it may be said that the mother plants have been open pollinated. Since the half-sibs often flower simultaneously, separating them from each other can be a costly procedure and is rarely worthwhile. For this reason the method is more frequently applied to crops that can be selected before flowering than to seed crops. Generally speaking, it may be said that half-sib selection is based on general combining ability, the entire population being used as a tester. A variant of the half-sib selection procedure is the polycross method. The polycross is particularly suitable for cross-pollinated crops which can be propagated and maintained vegetatively for purposes of breeding (e.g. many grasses and some legumes) . This procedure and its many variants have been used to develop a great number of synthetics. Full-sib Family Selection Here selection is carried out in the progeny of a mother plant which has been pollinated by only one father plant. Continued full-sib family selection leads to a rapid narrowing of the population. In effect, full-sib family selection is a test for specific combining ability. It is an effective means of selecting
against unfavourable characters, particularly against recessive alleles that can bedetectedbeforeflowering(1560 words)From Plant Breeding Perspectives by I. Sneep and A. J. T. P. HendriksenWords and expressionsAutogamousadj.自花授粉的Allogamousadj.异花授粉的Dioecyn.雌雄异株雌雄同株Monoecyn.hermaphroditen.雌雄同体n.去雄emasculationclone无性繁殖系n.adj.纯合的homozygousdialleladj.成双轮配的附属物adjunct n.等基因型isogenic linesimultaneouslyadv.同时地，同一地adj.隐性的recessive/ri'sesiv/ExercisesI. Fill in the blanks with the words from the text, the first and last letters and thenumber of the missing letters are given1. The energy needed to synthesize a gram of protein is about two times thatneededtosynthesizethesameamountofce.2. In order to achieve increased yield, the breeder may select for maximum dryweight at aS3. It is dangerous to think that breeding for disease re is nolonger necessary because the diseases can now be readily and cheaply controlled byfungicides.4. It is very important for breeders to consider that breeding varieties are tolerant18
18 against unfavourable characters, particularly against recessive alleles that can be detected before flowering. (1560 words) From Plant Breeding Perspectives by I. Sneep and A. J. T. P. Hendriksen Words and expressions Autogamous adj. 自花授粉的 Allogamous adj. 异花授粉的 Dioecy n. 雌雄异株 Monoecy n. 雌雄同株 hermaphrodite n. 雌雄同体 emasculation n. 去雄 clone n. 无性繁殖系 homozygous adj. 纯合的 diallel adj. 成双轮配的 adjunct n. 附属物 isogenic line 等基因型 simultaneously adv. 同时地，同一地 recessive /ri'sesiv/ adj. 隐性的 Exercises I. Fill in the blanks with the words from the text; the first and last letters and the number of the missing letters are given. 1. The energy needed to synthesize a gram of protein is about two times that needed to synthesize the same amount of c e. 2. In order to achieve increased yield, the breeder may select for maximum dry weight at a s. 3. It is dangerous to think that breeding for disease r e is no longer necessary because the diseases can now be readily and cheaply controlled by fungicides. 4. It is very important for breeders to consider that breeding varieties are tolerant
ofwaterdt.5.Thecommonas crops arewheat, rice, barley, soybean etc.6. In vegetatively p.d crops, improvement is achieved mainlythrough careful choice of parents, followed by the production of a large F1 populationandselectionforfavorablecharacteristics7.Improvement in autogamous crops began with the selection of wilds and then selection from land races.p8. By the end of 19th century, methods using crosses and back crosses as ac variability were being used.source ofg9. MLecrosses areusedto combinecharacteristicdistributed amongmore than two parents.10. Doubled hs result in a rapid evaluation of a particular crosscombination.Il.Fill intheblankswiththesuitableexpressionsbelowinthecorrectforms.diallel analysisland racerecessive alleleprotein contentlight soilhybrid productionmass selectiongenecombinationlineselectionnitrogenous fertilizer1.It is necessary for the plant breeders to consider grain yield as well asof their newvarieties.2.A fullis very difficult in many species.3. The experiments with wheat and barley grown onhave beendone.4.Selection in autogamous crops, male sterility is necessary for5. In developing countriesare still a wealth of adapted genotypes.6. If favorableare not to be lost in the course of earlygenerationslargenumbers of plants are required_and its7. Most of the current selection methods are based onmodifications.8. Full-sib family selection is an effective means of selecting againstthat can be detected before flowering.19
19 of water d t. 5. The common a s crops are wheat, rice, barley, soybean etc. 6. In vegetatively p d crops, improvement is achieved mainly through careful choice of parents, followed by the production of a large F1 population and selection for favorable characteristics. 7 .Improvement in autogamous crops began with the selection of wild p s and then selection from land races. 8. By the end of 19th century, methods using crosses and back crosses as a source of g c variability were being used. 9. M e crosses are used to combine characteristic distributed among more than two parents. 10. Doubled h s result in a rapid evaluation of a particular cross combination. II. Fill in the blanks with the suitable expressions below in the correct forms. diallel analysis land race recessive allele protein content hybrid production gene combination mass selection light soil line selection nitrogenous fertilizer 1. It is necessary for the plant breeders to consider grain yield as well as of their new varieties. 2. A full is very difficult in many species. 3. The experiments with wheat and barley grown on have been done. 4. Selection in autogamous crops, male sterility is necessary for . 5. In developing countries are still a wealth of adapted genotypes. 6. If favorable are not to be lost in the course of early generations, large numbers of plants are required. 7. Most of the current selection methods are based on and its modifications. 8. Full-sib family selection is an effective means of selecting against that can be detected before flowering
9.In cropsofminor economic importance,isnowused10.Protein content of any variety may be increased by appropriate applicationofI. Fill in the blanks with the English translation of Chinese given in thebrackets; you should add something where necessary to make them grammaticallycorrect.（就人类饮食而言），proteincontentisveryimportantin relation to bread making quality in wheat and to malting quality in barley.（根据其繁殖体2. Crops can be classified into three groups系)and the relevant methods of breeding3.（总的来说），half-sib selection is based on generalcombiningability.4. Selection in allogamous crops started with mass selection followed by such（半亲同胞加系选择和全亲同胞improvements as家系选择)。5. Because the half-sibs often flower at the same period, each mother plant（不只是由一个父本植物受精）。(植株6. A plant breeder may select for varieties in which全氮量的大部分）istranslocatedtothegrains.7. Research has showed that（矮秆品种）hadmorerootsatdepthsof50cmthantallerones8.（病毒对植物的侵染）constitutesagreatdangerduringthemaintenance and propagation9.（近缘种杂交）mayproducevariouskindsofresistance.(在系10. Favorable alleles may be lost in early generations谱选择方案中）IV. Select the best choice to complete the passage.Suppose a modemplant breeder wants(produce, to produce,producing) a new type of apple with a red 2(seed, flesh, skin), hard20
20 9. In crops of minor economic importance, is now used. 10. Protein content of any variety may be increased by appropriate application of . III. Fill in the blanks with the English translation of Chinese given in the brackets; you should add something where necessary to make them grammatically correct. 1. (就人类饮食而言) ，protein content is very important in relation to bread making quality in wheat and to malting quality in barley. 2. Crops can be classified into three groups (根据其繁殖体 系) and the relevant methods of breeding. 3． （总的来说），half-sib selection is based on general combining ability. 4. Selection in allogamous crops started with mass selection followed by such improvements as (半亲同胞加系选择和全亲同胞 家系选择)。 5. Because the half-sibs often flower at the same period, each mother plant （不只是由一个父本植物受精）。 6. A plant breeder may select for varieties in which (植株 全氮量的大部分) is translocated to the grains. 7. Research has showed that （矮秆品种）had more roots at depths of 50cm than taller ones. 8. (病毒对植物的侵染) constitutes a great danger during the maintenance and propagation. 9． （近缘种杂交）may produce various kinds of resistance. 10. Favorable alleles may be lost in early generations (在系 谱选择方案中). IV. Select the best choice to complete the passage. Suppose a modem plant breeder wants l (produce, to produce, producing) a new type of apple with a red 2 (seed, flesh, skin), hard