plateausn.平稳时期(单数为plateau)即将发生impendV.指数indexn.生物量biomassn.体细胞的somaticadj.胞质杂种cybridn.clonaladj.无性系的interspecificadj种间的相互的reciprocaladj.n.染色体组，基因组genome纯合性homozygosity隐性基因recessive gene二对等位基因的diallelicadj同源多倍体autopolyploidn.筛选vscreen突变型，突变体mutantn.抗代谢物antimetaboliten.Exercises1.Fill in the blanks with the information fromthe passage1.has led to the plant domestication during the past 5, o00years.2. In the futuretechnology will be used in plant breedingits3.In theory,plant breeding depends on the existence ofrecombination and selection of improved genotypes.4. In fact, cultivars,maybesourcesofvariation5.In plant breeding, some severe difficulties may arise because of lack ofrecombination with6.The final phase in plant breeding is the selection of improved genotypes6
6 plateaus n. 平稳时期(单数为 plateau) impend v. 即将发生 index n. 指数 biomass n. 生物量 somatic adj. 体细胞的 cybrid n. 胞质杂种 clonal adj. 无性系的 interspecific adj. 种间的 reciprocal adj. 相互的 genome n. 染色体组，基因组 homozygosity 纯合性 recessive gene 隐性基因 diallelic adj. 二对等位基因的 autopolyploid n. 同源多倍体 screen v 筛选 mutant n. 突变型，突变体 antimetabolite n. 抗代谢物 Exercises । .Fill in the blanks with the information from the passage. 1. has led to the plant domestication during the past 5, 000 years. 2. In the future, technology will be used in plant breeding. 3. In theory, plant breeding depends on the existence of , its recombination and selection of improved genotypes. 4. In fact, cultivars, may be sources of variation. 5. In plant breeding, some severe difficulties may arise because of lack of recombination with . 6. The final phase in plant breeding is the selection of improved genotypes
resultingfrom7.It is believed that about 50% of yield increase has resultedfrom8. The next major goal in plant breeding may be9. Some aspects ofare already used in plant breeding10.also provides a mechanism to broaden the germplasm baseI. Find in the text where the following ideas are expressed.1. The latest successes in plant breeding come from developments instatistics,mechanizationand computerization2.Future plant breeding will gradually incorporate various tissue culturetechniques.3. Most of the genetic base for improvement in crop yield has been providedby variability within the cultivated germplasm pool.4. Exotic germplasm has been successfully used in some crops5.Mutation isapossiblesourceof geneticvariation6. The numerous genes determine crop yield and quality7. Variability which results from recombination may be severely limited oreven disappear.8.Tissue culture in plant breeding helps overcome current restrictions in plantbreeding.9.Geneticimprovementcontributestoyieldincrease10. Tissue culture is also used in agronomic traitsAnswer the following question in detail.what methods have been developed in plant breeding by tissue culture according tothe passage?
7 resulting from 7. It is believed that about 50% of yield increase has resulted from . 8. The next major goal in plant breeding may be . 9. Some aspects of are already used in plant breeding. 10. also provides a mechanism to broaden the germplasm base. ॥. Find in the text where the following ideas are expressed. 1. The latest successes in plant breeding come from developments in statistics, mechanization and computerization 2. Future plant breeding will gradually incorporate various tissue culture techniques. 3. Most of the genetic base for improvement in crop yield has been provided by variability within the cultivated germplasm pool. 4. Exotic germplasm has been successfully used in some crops. 5. Mutation is a possible source of genetic variation. 6. The numerous genes determine crop yield and quality. 7. Variability which results from recombination may be severely limited or even disappear. 8. Tissue culture in plant breeding helps overcome current restrictions in plant breeding. 9. Genetic improvement contributes to yield increase. 10. Tissue culture is also used in agronomic traits. Answer the following question in detail. what methods have been developed in plant breeding by tissue culture according to the passage?
Part IIReading and PracticePassage IAims of crop breeding1.BreedingforIncreasedProteinYieldWhen selecting for increased grain yield, it is important that the plant breedershould at the same time consider the protein content of his new varieties. This isobviously important indeveloping countries, wherewheat comprises a largepartofthe human diet. But it is essential to view the problem in its proper perspective and inparticular to appreciate that protein content is of secondary importance when the totalenergy value of the diet is limiting.Under these circumstances proteins consumed willbe used as an additional source of energy and will not therefore be available forgrowth or tissue replacement.Nevertheless, programmes to breed wheat and barleyvarieties with in creased protein percentages, and with improved amino acid balanceof these proteins have been started in India and other developing countries. At thesame time, increased areas of wheat cultivation in these countries following theintroduction of highyieldingshort strawed varietieshas led to a reduction intheareadevoted to grain legumes such as chickpea .This has resulted in a reduction in theprotein content of the diet in some areas, and in particular in a fall in the content oflysine and other limiting amino acids.Even in Western Europe, cereals provide an important part of the protein in thehuman diet, and also in the diet of animals, which consume 47% of the wheatand 65% of the barley grown in the United Kingdom. So far as human diet isconcerned, protein content is most important in relation to bread making quality inwheat and tomalting quality in barley.When a range of wheat or barley varieties are grown under the same conditions,there is a strong negative association between protein percentage and grain yield,8
8 Part II Reading and Practice Passage I Aims of crop breeding 1. Breeding for Increased Protein Yield When selecting for increased grain yield, it is important that the plant breeder should at the same time consider the protein content of his new varieties. This is obviously important in developing countries, where wheat comprises a large part of the human diet. But it is essential to view the problem in its proper perspective and in particular to appreciate that protein content is of secondary importance when the total energy value of the diet is limiting. Under these circumstances proteins consumed will be used as an additional source of energy and will not therefore be available for growth or tissue replacement. Nevertheless, programmes to breed wheat and barley varieties with in creased protein percentages, and with improved amino acid balance of these proteins have been started in India and other developing countries. At the same time, increased areas of wheat cultivation in these countries following the introduction of high yielding short strawed varieties has led to a reduction in the area devoted to grain legumes such as chickpea . This has resulted in a reduction in the protein content of the diet in some areas, and in particular in a fall in the content of lysine and other limiting amino acids. Even in Western Europe, cereals provide an important part of the protein in the human diet, and also in the diet of animals, which consume 47% of the wheat and 65% of the barley grown in the United Kingdom. So far as human diet is concerned, protein content is most important in relation to bread making quality in wheat and to malting quality in barley. When a range of wheat or barley varieties are grown under the same conditions, there is a strong negative association between protein percentage and grain yield
though the protein content of any variety may be increased by appropriateapplications of nitrogenous fertilizer. This situation was demonstrated by Pushmanand Eingham who compared the yields of a range of winter wheat varieties grownunder three contrasting regimesThey also showed that despite the negativeregression of protein percentage on yield observed under each regime, certainvarieties consistently had higher protein contents than would have been expected fromthe overall regressions, suggesting that it should be possible for the plant breeder toselect for high yielding varieties with satisfactory protein content. They also showedthat the protein yield per hectare of modern varieties was up to 10% greater than thatof older varieties they had replaced.Despite the encouraging results obtained by Dobereiner, Day and von Bulowthere is no immediate likelihood of developing cereal plants capable of synthesisingproteins from atmospheric nitrogen. Increase in protein percentage can therefore onlybe achieved by selection for varieties which either assimilate soil nitrogen moreeffectively or which achieve a better distribution of protein within the plant. It ishowever important to appreciate that any increase in grain protein, whether byreduction of nitrate, or in the longer term by fixation of atmospheric nitrogen, canonlybe achieved by the expenditure of photosynthetic energy which might otherwisehave been used in the synthesis of carbohydrates.Furthermore, the energy required to synthesize a gramme of protein is aboutdouble that required to synthesize a gramme of carbohydrate.There are thus four ways in which selection for increased grain protein contentmay be attempted:() The breeder may select for maximum dry weight at anthesis. Such selectionmay also be necessary in order to achieve increased yield, though it may be difficultto combine with selection for shorter strawed varieties.(2) He may select for varieties which break the close correlation of total drymatter and protein content. Such varieties have been identified by Vogel, Johnsonand Mattern, and have been widely used in breeding programmes in many countries.(3) He may select for varieties in which a high proportion of total plant nitrogen9
9 though the protein content of any variety may be increased by appropriate applications of nitrogenous fertilizer. This situation was demonstrated by Pushman and Eingham who compared the yields of a range of winter wheat varieties grown under three contrasting regimes . They also showed that despite the negative regression of protein percentage on yield observed under each regime, certain varieties consistently had higher protein contents than would have been expected from the overall regressions, suggesting that it should be possible for the plant breeder to select for high yielding varieties with satisfactory protein content. They also showed that the protein yield per hectare of modern varieties was up to 10% greater than that of older varieties they had replaced. Despite the encouraging results obtained by Dobereiner, Day and von Bulow there is no immediate likelihood of developing cereal plants capable of synthesising proteins from atmospheric nitrogen. Increase in protein percentage can therefore only be achieved by selection for varieties which either assimilate soil nitrogen more effectively or which achieve a better distribution of protein within the plant. It is however important to appreciate that any increase in grain protein, whether by reduction of nitrate, or in the longer term by fixation of atmospheric nitrogen, can only be achieved by the expenditure of photosynthetic energy which might otherwise have been used in the synthesis of carbohydrates. Furthermore, the energy required to synthesize a gramme of protein is about double that required to synthesize a gramme of carbohydrate. There are thus four ways in which selection for increased grain protein content may be attempted: (1) The breeder may select for maximum dry weight at anthesis. Such selection may also be necessary in order to achieve increased yield, though it may be difficult to combine with selection for shorter strawed varieties. (2) He may select for varieties which break the close correlation of total dry matter and protein content. Such varieties have been identified by Vogel, Johnson and Mattern, and have been widely used in breeding programmes in many countries. (3) He may select for varieties in which a high proportion of total plant nitrogen
is translocated to the grain.Austin et al.report significant differences in this ratio,defined as nitrogen harvest index, though high values may be associated with varietiesin which photosynthetic activity of the leaves and ears falls off more rapidly afteranthesis,leaving moretimeforthetranslocation of nitrogen from those organstothe grain.(4) Finally he may select for genotypes in which nitrogen uptake continues afteranthesis, but the metabolic energy required for this process may again be associatedwith genotypes with long continued Photosynthetic activity, and hence with lowernitrogenharvest index.2.BreedingforReliability of PerformanceAny analysis of theprospects of breeding for yield must consider also problemsof breeding for reliability of performance and the need for more widespread use ofimproved husbandry techniques so as to narrow the gap between national averageyields and those obtained by the best farmers. Detailed consideration of problems ofdisease and pest control lie outside the scope of the present review, though losses dueto these organisms are one of the principal causes of year to year variations in yieldMention should however be made of the recent work on breeding for durableresistance to leaf diseases and the use of mixtures and multilines in order to limit therisk of losses due to newly arising virulent races especially of airborne pathogensattackingleavesandstems.It has been suggested that work on breeding for disease resistance is no longernecessary because the diseases can now be readily and cheaply controlled byfungicides. But I consider this a dangerous concept, partly because the cost offungicides and their application is likely to increase, but more particularly because ofthe veryreal dangerthat strains of thepathogens may develop withvirulence againstsprayed crops.Such virulence has already been reported on several occasions, as inthecaseof ethirimol(乙菌定)toleranceofpowderymildewinbarleyIthereforesuggest that although fungicides have a very valuable role to play, their action shouldbe monitored in variety trials with untreated controls.This should lead to anintegrated control system in which losses are restricted by the use of low rates of10
10 is translocated to the grain. Austin et al. report significant differences in this ratio, defined as nitrogen harvest index, though high values may be associated with varieties in which photosynthetic activity of the leaves and ears falls off more rapidly after anthesis, leaving more time for the translocation of nitrogen from those organs to the grain. (4) Finally he may select for genotypes in which nitrogen uptake continues after anthesis, but the metabolic energy required for this process may again be associated with genotypes with long continued Photosynthetic activity, and hence with lower nitrogen harvest index. 2. Breeding for Reliability of Performance Any analysis of the prospects of breeding for yield must consider also problems of breeding for reliability of performance and the need for more widespread use of improved husbandry techniques so as to narrow the gap between national average yields and those obtained by the best farmers. Detailed consideration of problems of disease and pest control lie outside the scope of the present review, though losses due to these organisms are one of the principal causes of year to year variations in yield. Mention should however be made of the recent work on breeding for durable resistance to leaf diseases and the use of mixtures and multilines in order to limit the risk of losses due to newly arising virulent races especially of airborne pathogens attacking leaves and stems. It has been suggested that work on breeding for disease resistance is no longer necessary because the diseases can now be readily and cheaply controlled by fungicides. But I consider this a dangerous concept, partly because the cost of fungicides and their application is likely to increase, but more particularly because of the very real danger that strains of the pathogens may develop with virulence against sprayed crops. Such virulence has already been reported on several occasions, as in the case of ethirimol(乙菌定) tolerance of powdery mildew in barley. I therefore suggest that although fungicides have a very valuable role to play, their action should be monitored in variety trials with untreated controls. This should lead to an integrated control system in which losses are restricted by the use of low rates of