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Preface: Ideotypes and physiology: tailoring plants for increased production
FieldCropsResearch, 26 ( 1991) 89-92 ElsevierSciencePublishersB.V., Amsterdam
89
Preface: Ideotypes and physiology: tailoring plants for increased production The contributions to this special issue of Field Crops Research are based on presented papers and discussions at a Workshop on Ideotypes and Physiology: Tailoring Plants for Increased Production, held in conjunction with the 5th Australian Agronomy Conference in Perth, Western Australia, 23-24 February 1990. The workshop was stimulated by the fact that 21 years had passed since Donald ( 1968 ) first proposed the concept of an 'ideotype' and by the realisation that enough time had elapsed to evaluate the concept and to assess what progress had been made in harnessing the resources of plant physiology towards breeding crops with a greater yield potential than their predecessors. Australia has a diversity of climates, ranging from cool temperate and mediterranean in the south (receiving predominantly winter rainfall ), to subtropical in the eastern part of the continent, and tropical in the northern region (predominantly summer rainfall). Throughout these regions, and for many years, a number of organisations and centres have been involved in the improvement of a wide array of field crops. Hence the Australian cropping regions collectively provide a laboratory in which to study and review the application of a diversity of approaches to crop improvement, and to assess progress and possible future directions. Plant physiologists have long been interested in the application of physiological approaches to plant breeding, but it was Donald who developed a physiologically comprehensive theory of breeding for higher seed yields, which clearly differed from traditional plant breeding approaches. In the introductory paper to this special issue, one of us (RHS) reviews the background to the ideotype concept as applied to the drier areas of the southwestern Australian cereal belt for 20 years, and attempts to define ideotypes of spring wheat and alternative crops suitable for the region. He concludes that, despite problems of implementation, the concept has much to offer towards attaining plant breeding objectives. The main value of an ideotype is seen as providing a structure to define breeding objectives in terms of plant characters; where the concept has been tested, the hypothesis of the weak competitor (e.g. in uniculm or low-tillering wheats) is supported, with some qualifications. Lawn and Imrie (p. 113 ) discuss the role of physiological understanding in breeding for crop improvement, and minimising environmental constraints to achieving yield potential in northern Australia. Many of the crops grown 0378-4290/91/$03.50
© 1991-- ElsevierSciencePublishersB.V.
90
R.H. SEDGLEY AND R.K. BELFORD
in this environment are new to Australia, and are traditionally strongly sensitive to photoperiod and temperature (e.g. the grain legumes soybean and mungbean, and the cereal sorghum). A primary aim of crop-improvement programmes is thus to increase crop adaptation to the warm-temperature/ short-photoperiod environment of the tropics and sub-tropics. Constraints are also imposed by high temperatures, and highly variable and sometimes limited seasonal rainfall, compounded by soils with low water-holding capacities. In this northern environment, physiological research is being used to identify key physiological constraints to crop improvement, to establish agronomic and breeding research strategies, and thus to identify appropriate ideotypes for the target environment. In addition, much of this physiological understanding can now be used in models to predict crop performance in particular environments. In the temperate and mediterranean environments of southern Australia, cropping is dominated by temperate crops, particularly wheat (Richards, p. 141 ). The major environmental constraints to productivity are frost after stem elongation and during heading of cereals, and a lack of water in spring when evaporative demand is rising rapidly. Characteristics which offer good prospects for improving yields thus fall into the categories of appropriate phenology, high water-use efficiency and high harvest index, and are identified in this paper. Marshall (p. 171 ) compares the ideotype approach with alternative approaches to breeding for higher yields. He argues that ideotype breeding suffers from conceptual and practical problems. Conceptual problems are the assumption that there is an optimal phenotype for a given environment, the difficulty of identifying traits that could lead to yield improvement, and the problems of evaluating self-competition in monocultures. Practical problems are the lack of appropriate genetic diversity for many crop plants, the existence of strong inter-relationships among traits, and pleiotropic effects. Alternative approaches to increasing yield potential include using Fl hybrids, and restricted-fragment-length polymorphisms (RFLP's) to track and manipulate gene loci controlling yield. There should also be a continuing emphasis on reducing constraints to yields of current genetic material, including strategies for the effective use of the erratic and limiting rainfall in many parts of Australia, control of soil and airborne pathogens, tolerance of mineral deficiencies or toxicities (including the increasing problem of soil acidity ), and resistance to frost damage during reproductive development in cereals. Rasmusson (p. 191 ) is a plant breeder who has actively used ideotype traits in improvement programmes for barley in the northern U.S.A. In his paper he recognises that, while traditional breeding will continue to be dominant in improving crop yield potential, ideotype breeding could complement traditional approaches by setting targets for traits of interest and potential yield
IDEOTYPESANDPHYSIOLOGY:PREFACE
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advantage. Most cereal plant breeders have, consciously or subconsciously, selected for ideotype traits such as height, tiller/head number, grain weight, and leaf angle. The difficulty is in finding which traits are most likely to benefit yield, and determining the optimum combination of these traits, i.e. phenotype; this implies physiological input into plant breeding programmes. Thurling presents a paper (p. 201 ) to show how the definition of a yield ideotype can be used to improve the efficiency of breeding for higher yields in oilseed brassicas, and discusses the application of biometrical genetic analysis to improve yield breeding methodology. Overall, biometrical genetics has not been particularly successful in improving yield in self-pollinating plants, largely because of the complex inheritance of yield, and the necessity to use low-density plant populations to estimate genetic parameters. This latter is one of the major problems that Donald ( 1968 ) originally addressed in formulating the ideotype. Thurling proposes a more productive approach to yield improvement as likely to come from manipulation of simple morphological characters that have an influence on the physiological processes determining seed yields. Here, the ideotype concept leads to a more rational approach to yield improvement by combining physiologically based yield characters in a superior cultivar. Improvement of Brassica napus using an ideotype approach can utilise the enormous genetic diversity in related brassica species, particularly B. campestris and B. juncea. At the conclusion of the formal presentations, delegates were allocated to groups according to their crop interests - - pastures, sunflower, brassicas, barley, other cereals (mediterranean, or summer-rainfall/sub-tropical), and grain legumes (mediterranean, or summer-rainfall/sub-tropical) - - with the objective of encouraging dialogue between the breeders, agronomists and physiologists in each group. Groups were asked to: ( 1 ) consider general questions about the relations between physiologists and breeders, and the role that physiological research might contribute to breeding for crop improvement; (2) undertake an analysis of the specific factors that are important in improving the crop in the environment chosen by each group; and (3) identify the constraints to crop improvement, and outline techniques that would be most likely to overcome them for the particular crop. The results of these discussions are presented in the final paper of this issue (p. 221 ).
REFERENCES Donald, C.M., 1968. The breeding of crop ideotypes. Euphytica, 17: 385-403.
92
R.H. SEDGLEY AND R.K. BELFORD
R.H. SEDGLEY
Crop and Pasture Sciences Group, School of Agriculture, University of Western Australia, Nedlands, WA 6009, Australia R.K. BELFORD
Western Australian Department of Agriculture, Baron-Hay Court, South Perth, WA 6151, Australia
89
Preface: Ideotypes and physiology: tailoring plants for increased production The contributions to this special issue of Field Crops Research are based on presented papers and discussions at a Workshop on Ideotypes and Physiology: Tailoring Plants for Increased Production, held in conjunction with the 5th Australian Agronomy Conference in Perth, Western Australia, 23-24 February 1990. The workshop was stimulated by the fact that 21 years had passed since Donald ( 1968 ) first proposed the concept of an 'ideotype' and by the realisation that enough time had elapsed to evaluate the concept and to assess what progress had been made in harnessing the resources of plant physiology towards breeding crops with a greater yield potential than their predecessors. Australia has a diversity of climates, ranging from cool temperate and mediterranean in the south (receiving predominantly winter rainfall ), to subtropical in the eastern part of the continent, and tropical in the northern region (predominantly summer rainfall). Throughout these regions, and for many years, a number of organisations and centres have been involved in the improvement of a wide array of field crops. Hence the Australian cropping regions collectively provide a laboratory in which to study and review the application of a diversity of approaches to crop improvement, and to assess progress and possible future directions. Plant physiologists have long been interested in the application of physiological approaches to plant breeding, but it was Donald who developed a physiologically comprehensive theory of breeding for higher seed yields, which clearly differed from traditional plant breeding approaches. In the introductory paper to this special issue, one of us (RHS) reviews the background to the ideotype concept as applied to the drier areas of the southwestern Australian cereal belt for 20 years, and attempts to define ideotypes of spring wheat and alternative crops suitable for the region. He concludes that, despite problems of implementation, the concept has much to offer towards attaining plant breeding objectives. The main value of an ideotype is seen as providing a structure to define breeding objectives in terms of plant characters; where the concept has been tested, the hypothesis of the weak competitor (e.g. in uniculm or low-tillering wheats) is supported, with some qualifications. Lawn and Imrie (p. 113 ) discuss the role of physiological understanding in breeding for crop improvement, and minimising environmental constraints to achieving yield potential in northern Australia. Many of the crops grown 0378-4290/91/$03.50
© 1991-- ElsevierSciencePublishersB.V.
90
R.H. SEDGLEY AND R.K. BELFORD
in this environment are new to Australia, and are traditionally strongly sensitive to photoperiod and temperature (e.g. the grain legumes soybean and mungbean, and the cereal sorghum). A primary aim of crop-improvement programmes is thus to increase crop adaptation to the warm-temperature/ short-photoperiod environment of the tropics and sub-tropics. Constraints are also imposed by high temperatures, and highly variable and sometimes limited seasonal rainfall, compounded by soils with low water-holding capacities. In this northern environment, physiological research is being used to identify key physiological constraints to crop improvement, to establish agronomic and breeding research strategies, and thus to identify appropriate ideotypes for the target environment. In addition, much of this physiological understanding can now be used in models to predict crop performance in particular environments. In the temperate and mediterranean environments of southern Australia, cropping is dominated by temperate crops, particularly wheat (Richards, p. 141 ). The major environmental constraints to productivity are frost after stem elongation and during heading of cereals, and a lack of water in spring when evaporative demand is rising rapidly. Characteristics which offer good prospects for improving yields thus fall into the categories of appropriate phenology, high water-use efficiency and high harvest index, and are identified in this paper. Marshall (p. 171 ) compares the ideotype approach with alternative approaches to breeding for higher yields. He argues that ideotype breeding suffers from conceptual and practical problems. Conceptual problems are the assumption that there is an optimal phenotype for a given environment, the difficulty of identifying traits that could lead to yield improvement, and the problems of evaluating self-competition in monocultures. Practical problems are the lack of appropriate genetic diversity for many crop plants, the existence of strong inter-relationships among traits, and pleiotropic effects. Alternative approaches to increasing yield potential include using Fl hybrids, and restricted-fragment-length polymorphisms (RFLP's) to track and manipulate gene loci controlling yield. There should also be a continuing emphasis on reducing constraints to yields of current genetic material, including strategies for the effective use of the erratic and limiting rainfall in many parts of Australia, control of soil and airborne pathogens, tolerance of mineral deficiencies or toxicities (including the increasing problem of soil acidity ), and resistance to frost damage during reproductive development in cereals. Rasmusson (p. 191 ) is a plant breeder who has actively used ideotype traits in improvement programmes for barley in the northern U.S.A. In his paper he recognises that, while traditional breeding will continue to be dominant in improving crop yield potential, ideotype breeding could complement traditional approaches by setting targets for traits of interest and potential yield
IDEOTYPESANDPHYSIOLOGY:PREFACE
91
advantage. Most cereal plant breeders have, consciously or subconsciously, selected for ideotype traits such as height, tiller/head number, grain weight, and leaf angle. The difficulty is in finding which traits are most likely to benefit yield, and determining the optimum combination of these traits, i.e. phenotype; this implies physiological input into plant breeding programmes. Thurling presents a paper (p. 201 ) to show how the definition of a yield ideotype can be used to improve the efficiency of breeding for higher yields in oilseed brassicas, and discusses the application of biometrical genetic analysis to improve yield breeding methodology. Overall, biometrical genetics has not been particularly successful in improving yield in self-pollinating plants, largely because of the complex inheritance of yield, and the necessity to use low-density plant populations to estimate genetic parameters. This latter is one of the major problems that Donald ( 1968 ) originally addressed in formulating the ideotype. Thurling proposes a more productive approach to yield improvement as likely to come from manipulation of simple morphological characters that have an influence on the physiological processes determining seed yields. Here, the ideotype concept leads to a more rational approach to yield improvement by combining physiologically based yield characters in a superior cultivar. Improvement of Brassica napus using an ideotype approach can utilise the enormous genetic diversity in related brassica species, particularly B. campestris and B. juncea. At the conclusion of the formal presentations, delegates were allocated to groups according to their crop interests - - pastures, sunflower, brassicas, barley, other cereals (mediterranean, or summer-rainfall/sub-tropical), and grain legumes (mediterranean, or summer-rainfall/sub-tropical) - - with the objective of encouraging dialogue between the breeders, agronomists and physiologists in each group. Groups were asked to: ( 1 ) consider general questions about the relations between physiologists and breeders, and the role that physiological research might contribute to breeding for crop improvement; (2) undertake an analysis of the specific factors that are important in improving the crop in the environment chosen by each group; and (3) identify the constraints to crop improvement, and outline techniques that would be most likely to overcome them for the particular crop. The results of these discussions are presented in the final paper of this issue (p. 221 ).
REFERENCES Donald, C.M., 1968. The breeding of crop ideotypes. Euphytica, 17: 385-403.
92
R.H. SEDGLEY AND R.K. BELFORD
R.H. SEDGLEY
Crop and Pasture Sciences Group, School of Agriculture, University of Western Australia, Nedlands, WA 6009, Australia R.K. BELFORD
Western Australian Department of Agriculture, Baron-Hay Court, South Perth, WA 6151, Australia