The breeding of crop ideotypes
TL;DR: It is postulated that a successful crop ideotype will be a weak competitor, relative to its mass, and the like plants in the crop community will compete with each other to a minimum degree.
Abstract: Most plant breeding is based on “defect elimination” or “selection for yield”. A valuable additional approach is available through the breeding of crop ideotypes, plants with model characteristics known to influence photosynthesis, growth and (in cereals) grain production. Some instances of the successful use of model characters of this kind are quoted.
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TL;DR: In this article, the authors discuss N dynamics in soil plant systems, and outline management options for enhancing N use by annual crops, including livestock production with cropping, to improve N efficiency in agriculture.
Abstract: Nitrogen is the most limiting nutrient for crop production in many of the world's agricultural areas and its efficient use is important for the economic sustainability of cropping systems Furthermore, the dynamic nature of N and its propensity for loss from soil‐plant systems creates a unique and challenging environment for its efficient management Crop response to applied N and use efficiency are important criteria for evaluating crop N requirements for maximum economic yield Recovery of N in crop plants is usually less than 50% worldwide Low recovery of N in annual crop is associated with its loss by volatilization, leaching, surface runoff, denitrification, and plant canopy Low recovery of N is not only responsible for higher cost of crop production, but also for environmental pollution Hence, improving N use efficiency (NUE) is desirable to improve crop yields, reducing cost of production, and maintaining environmental quality To improve N efficiency in agriculture, integrated N management strategies that take into consideration improved fertilizer along with soil and crop management practices are necessary Including livestock production with cropping offers one of the best opportunities to improve NUE Synchrony of N supply with crop demand is essential in order to ensure adequate quantity of uptake and utilization and optimum yield This paper discusses N dynamics in soil‐plant systems, and outlines management options for enhancing N use by annual crops
1,083 citations
TL;DR: Maize (Zea mays L.) yields have risen continually wherever hybrid maize has been adopted, starting in the U.S. corn belt in the early 1930s, and genetic gains may have to bear a larger share of the load in future years.
Abstract: Maize (Zea mays L.) yields have risen continually wherever hybrid maize has been adopted, starting in the U.S. corn belt in the early 1930s. Plant breeding and improved management practices have produced this gain jointly. On average, about 50% of the increase is due to management and 50% to breeding. The two tools interact so closely that neither of them could have produced such progress alone. However, genetic gains may have to bear a larger share of the load in future years. Hybrid traits have changed over the years. Trait changes that increase resistance to a wide variety of biotic and abiotic stresses (e.g., drought tolerance) are the most numerous, but morphological and physiological changes that promote efficiency in growth, development, and partitioning (e.g., smaller tassels) are also recorded. Some traits have not changed over the years because breeders have intended to hold them constant (e.g., grain maturity date in U.S. corn belt). In other instances, they have not changed, despite breeders' intention to change them (e.g., harvest index). Although breeders have always selected for high yield, the need to select simultaneously for overall dependability has been a driving force in the selection of hybrids with increasingly greater stress tolerance over the years. Newer hybrids yield more than their predecessors in unfavorable as well as favorable growing conditions. Improvement in the ability of the maize plant to overcome both large and small stress bottlenecks, rather than improvement in primary productivity, has been the primary driving force of higher yielding ability of newer hybrid.
950 citations
TL;DR: In this article, a hypothetical ideotype is presented to optimize water and N acquisition by maize root systems, based on the coincidence of root foraging and resource availability in time and space.
896 citations
TL;DR: The chapter examines the interaction of biological yield, grain yield, and harvest index with plant density and the situation in which a number of varieties have precisely the same biological yield but different grain yields is graphically presented.
Abstract: Publisher Summary The chapter discusses the meaning and value of the biological yield and harvest index of cereals in agronomic studies and in cereal breeding. The relationship of biological yield, grain yield, and harvest index to each other and to other plant characteristics is discussed. Various models and actual relationships between biological yields and grain yields within a series of genotypes or agronomic treatments are described. The situation in which a number of varieties have precisely the same biological yield but different grain yields is graphically presented along with the genotypes that are ranked in order of increasing grain yield. Grain yield is proportional to harvest index and their correlation is 1.00, whereas biological yield and harvest index are unrelated. The chapter examines the interaction of biological yield, grain yield, and harvest index with plant density. Biological yield and harvest index are two valuable criteria for the assessment of the performance of cereals.
811 citations
TL;DR: The authors need a new way to classify, describe and analyze plant allocation and plasticity because the concepts ‘trait’ and ‘plasticity’ are too broad.
Abstract: Allocation is one of the central concepts in modern ecology, providing the basis for different strategies. Allocation in plants has been conceptualized as a proportional or ratio-driven process (‘partitioning’). In this view, a plant has a given amount of resources at any point in time and it allocates these resources to different structures. But many plant ecological processes are better understood in terms of growth and size than in terms of time. In an allometric perspective, allocation is seen as a size-dependent process: allometry is the quantitative relationship between growth and allocation. Therefore most questions of allocation should be posed allometrically, not as ratios or proportions. Plants evolve allometric patterns in response to numerous selection pressures and constraints, and these patterns explain many behaviours of plant populations. In the allometric view, plasticity in allocation can be understood as a change in a plant's allometric trajectory in response to the environment. Some allocation patterns show relatively fixed allometric trajectories, varying in different environments primarily in the speed at which the trajectory is travelled, whereas other allocation patterns show great flexibility in their behaviour at a given size. Because plant growth is often indeterminate and its rate highly influenced by environmental conditions, ‘plasticity in size’ is not a meaningful concept. We need a new way to classify, describe and analyze plant allocation and plasticity because the concepts ‘trait’ and ‘plasticity’ are too broad. Three degrees of plasticity can be distinguished: (1) allometric growth (‘apparent plasticity’), (2) modular proliferation and local physiological adaptation, and (3) integrated plastic responses. Plasticity, which has evolved because it increases individual fitness, can be a disadvantage in plant production systems, where we want to optimize population, not individual, performance.
729 citations
Cites background from "The breeding of crop ideotypes"
...Put in the language of evolutionary theory, agronomist C.M. Donald’s concept of the crop ‘ideotype’ (Donald 1968) was that crop breeders should practice group- not individual selection, since not all attributes that increase individual yield are advantageous for population yield....
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...Donald’s concept of the crop ‘ideotype’ (Donald 1968) was that crop breeders should practice group- not individual selection, since not all attributes that increase individual yield are advantageous for population yield....
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References
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01 Jan 1953
1,612 citations
TL;DR: The fuller understanding of competition among plants requires a greater knowledge of the response of plants to their environment, especially of theresponse to the environmental stresses created by neighbors.
Abstract: Publisher Summary In the early days of agriculture, man must have learned of the competition among individual plants within a crop or intraspecific competition, even though his knowledge was purely in empirical terms. He must have learned by experience that if the sowing rate were sparse, his harvest would be lean, and conversely that if the seed rate were increased beyond a certain value, the plants would be spindly and poorly grown. The fuller understanding of competition among plants requires a greater knowledge of the response of plants to their environment, especially of the response to the environmental stresses created by neighbors. Plant physiologists have studied the single plant, and agronomists have looked at the whole crop, but the plant within the community has scarcely been investigated. This is a field which promises both scientific depth and great potential reward in terms of crop production.
720 citations
01 Mar 1967
TL;DR: The amount of photosynthesis accomplished by a canopy of leaves is predicted from the properties of individual leaves, providing new insights into the photosynthetic behavior of plant communities.
Abstract: In this paper, the amount of photosynthesis accomplished by a canopy of leaves is
predicted from the properties of individual leaves. Theories are developed for the
penetration of direct and diffuse sunlight through a foliage composed of many layers
of leaves, each having known orientation, area, reflection and transmission characteristics.
From this, the illumination of each leaf at a particular time of day (sun elevation)
and thus its photosynthesis, is determined. Hourly observations are summed for estimates
of daily photosynthesis by plant communities.
An immense number of calculations are required in such a model, but an IBM 7044-type
computer can complete them in about six seconds. Solutions to a number of real and
hypothetical problems are presented. These provide new insights into the photosynthetic
behavior of plant communities.
380 citations
TL;DR: An experiment was undertaken with wheat to study the effects of interplant competition on dry matter and grain production and it is suggested that the application of this type of analysis to the reaction of different genotypes to crowding may add to an understanding of crop performance.
Abstract: An experiment was undertaken with wheat (cv. Insignia 49) to study the effects of interplant competition on dry matter and grain production. Crops ranging in density from 1.4 to 1078 plants per sq. metre were established, and light intensity and growth measurements were made within the crop. Four sequential stages in the growth of the crop were recognized, namely: A period in which there was no interplant competition at any density. A period in which the crop growth rate showed a curvilinear relationship to the leaf area index and a linear relationship to light interception. A period when the weight of ears (early dough stage) showed a linear relationship to an expression involving the weight of green leaf in an earlier period and the percentage survival of tillers. A period of grain filling and ripening in which some further relative changes in ear and grain weight occurred. It is suggested that the application of this type of analysis to the reaction of different genotypes to crowding may add to an understanding of crop performance.
189 citations
"The breeding of crop ideotypes" refers background in this paper
...At such a seed rate, the plants will be extremely depauperate, and the yield per unit area will be less than at a lower seed rate (PUCKRIDGE and DONALD, 1967)....
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156 citations
"The breeding of crop ideotypes" refers background in this paper
...BEACHELL, H. M. and JENNINGS, P. R., 1965....
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...However NICHIPOROVIC (1954) and many others have emphasized that total production (biological yield) is an insufficient criterion of crop yield when the economic yield comprises only a part of the plant, such as its grain, fibre or oil. Assuming that the model is capable of heavy dry matter production (net photosynthesis), a further feature must be its capacity to render a maximum part of that yield as the useful product. Nichiporovic terms this ratio of ‘economic yield’ to ‘biological yield’, the ‘coefficient of effectiveness of formation of the economic part of the total yield’; DONALD (1962) has suggested the term ‘harvest index’....
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...(“Prolific” here means a capacity to produce a second ear at wide spacing). Shade tolerance by the whole plant is also a feature of successful hybrids (STINSON AND Moss, 1960), while HAGEMAN et al. (1967) suggest that the levels of activity of enzymes such as nitrate reductase may ultimately provide bree-...
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...KASANAOA, H. and MONSI, M., 1954....
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...KASPER, R. E., 1929....
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