Biochemical Basis of Plant Breeding

Volume 1 Carbon Metabolism

Carlos A. Neyra

• Éditeur: CRC Press
• Année: 2019
• ISBN:
  9781000697629
• Édition: 1
• Sujet: Biological Sciences
• Sous-sujet: Science General

First published in 1985: This book presents a comprehensive survey of progress and current knowledge of those biochemical processes with greater potential for the development of superior cultivars: Photosynthesis, photorespiration, nitrate assimilation, biological nitrogen fixation, and starch and protein synthesis.

Part I
Introductory Chapters

Chapter 1

Plant Breeding: Biochemistry and Crop Productivity

Carlos A. Neyra

TABLE OF CONTENTS

• I. Introduction
• II. Plant Breeding and Crop Productivity
  • A. Food Crops and Partitioning of Assimilates
  • B. Wheat, Rice, and Corn Breeding
  • C. Grain Legumes
  • D. Root and Tuber Crops
• III. Plant Biochemistry and Breeding Research
  • A. An Overview
  • B. Gene Mutations and Cellular Approaches to Breeding
  • C. Protein Quantity and Quality
• Acknowledgments
• References

I. Introduction

One of the major challenges for scientists, at present, is to help increase effectively world food production to meet the ever increasing demands of a rapidly expanding population. A projection of current statistical figures indicates that world population will reach 8 billion by the first decade of the 21st century.¹ By that time, food supply will still be dependent, for the most part, on agricultural farming, but the efficiency of utilization of cultivated land will have to be greatly improved by the adoption of better farming practices and the development of new genotypes capable of achieving higher yields than those currently under cultivation.

The significant growth of agricultural productivity over the past few decades can be attributed in large part to the application of modern concepts of genetics to the breeding of superior crops. Most of the gains have come from the exploitation of the genetic diversity present in species that have long been domesticated but so far, all genotypes available for farming have been developed by conventional methods based on pheno-typic characters associated with crop yields. To some extent, the goal of increasing crop productivity and the rate of achievements depends on our ability to understand and manipulate the biochemical and genetic mechanisms controlling plant productivity. Several biochemical criteria have been proposed for the selection of superior cultivars and have been under evaluation for almost 25 years. Yet, they are still to be implemented into a successful plant breeding program of economic importance.

This book presents a comprehensive survey of progress and current knowledge of those biochemical processes with greater potential for the development of superior cultivars: photosynthesis, photorespiration, nitrate assimilation, biological nitrogen fixation, and starch and protein synthesis. Each chapter addresses the major features of the physiological processes involved: the indentification of rate-limiting steps; regulatory properties of key enzymes; and a discussion of alternatives to overcome the limitations for enhanced crop productivity.

The contents of this book are presented in two volumes: Carbon Nutrition (Volume I) and Nitrogen Nutrition (Volume II). Throughout the contents, we have attempted to provide sufficient background information and discussion of biochemical tools to strengthen the approach and goals of plant breeding programs. Special attention was given to analyze the possibility of using genetic engineering methods for raising the genetic yield potential of crops. Modern plant breeding, in the context of this book, is seen as a combination of both the conventional or traditional plant breeding approach with the more novel molecular and cellularly based genetic engineering methodologies.

Because of the vast knowledge needed to make an in-depth presentation of the subjects under consideration, I chose to invite some of the best regarded scientists to contribute with their expertise to this book. As the editor, I was also responsible for the selection of the topics to be included. Within broad editorial guidelines, the contributors have been responsible for the precise content and approach of their chapters. A list of contributors and their institutional affiliations has been included for anyone willing to make further contacts and expand on the topics covered under this book.

II. Plant Breeding and Crop Productivity

A. Food Crops and Partitioning of Assimilates

The welfare of mankind largely depends upon plants as a source of food and fiber. Of all plants known to have economical value (about 1500 species), only a few (around 30 species) have been developed as food crops.^1,2,3 One half of those species (eight cereals and seven legumes) is known as grain crops (pulses in the case of legumes), and these provide most of the calories and protein for human nutrition. In fact, 50% of those requirements is met by only three cereal crops: wheat, rice, and corn. Among the pulses, soybeans (Glycine max) and drybeans (Phaseolus vulgaris) are the most important food crops. Potatoes (Solanum tuberosum) and cassava (Manihot esculenta) are the most important among the crops harvested for their underground parts.⁴ All of the crops cited above have been developed because of their capability to mobilize and accumulate in defined structures of the plant a large proportion of their biosynthetic production. Thus, the increase of the genetic yield potential, within a given crop species, has usually been accompanied by an increase in harvest index (dry matter accumulated in storage organs/total dry matter produced by the plant).^1,5,6,7,8,9

The partitioning of assimilates among various plant parts is of major importance for agricultural productivity. We also know that an important variation exists in the relative allocation of dry matter to different organs. Crops grown for their vegetative aerial portion tend to reinvest more into the development of new leaves. Grain crops, on the other hand, tend to allocate more assimilates into the production of reproductive structures, and other crops (potato, cassava, etc.) invest relatively more into the underground plant parts. However, we know relatively very little about the physiological and biochemical mechanisms controlling a defined pattern of assimilate partitioning. Research in these areas should help provide the knowledge needed to devise modern plant breeding strategies. Further understanding of the specific nature of assimilate partitioning may lead to further manipulation of harvest indexes and maximization of reproductive yields in grain crops and vegetative yields in forage and root crops.

In principle, assimilate partitioning is based upon the relative strength of source and sink structures. Source tissues are those capable of exporting assimilates. Sinks, on the other hand, are represented by structures that exhibit a net import of assimilates, and their activity will be dependent upon size, position in relation to the source, geometry, physiological stage, and competition among different sinks.^5,9 All actively growing, storing, or metabolizing tissues may be considered as strong sinks. Mobilization of assimilates from source to sink occurs primarily via phloem.^9,10 Sucrose (and, to a lesser extent, amino acids) is universally recognized as the main form of carbon transported. Organic nitrogen, on the other hand, is primarily transported in the form of amino acids.^9,10 The interrelationships between primary carbon assimilation, and sucrose and starch metabolism are schematically presented in Figure 1 and will be discussed in more detail in Chapters 6 and 8 (Volume I). The interrelationships between the primary assimilation of inorganic nitrogen, temporary storage of organic nitrogen in vegetative structures, and the remobilization and transport of organic nitrogen to the seeds are also shown in Figure 1. For further details, see Chapters 4 and 5 (Volume II) and also Pate,¹⁰ Below et al.,¹¹ Miflin and Lea,¹² and Reed et al.¹³

B. Wheat, Rice, and Corn Breeding

Plant breeders have been successful in developing cultivars that allocate a larger proportion of their assimilates to the harvestable organ without increasing the total biomass production (dry matter/ha), and this suggested that a genetic basis for partitioning exists.^1,5,9 In wheat and rice, the release of semi-dwarf varieties with an improve...

Table des matières

• Cover
• Title Page
• Copyright Page
• The Editor
• Contributors
• Table of Contents
• Part I: Introductory Chapters
• Part II: Carbon Nutrition
• Index