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NUNC COGNOSCO EX PARTE TRENT UNIVERSITY LIBRARY Digitized by the Internet Archive in 2019 with funding from Kahle/Austin Foundation https://archive.org/details/principlesofplanOOOOalla PLANT BREEDING principles of PLANT principles of R. W. ALLARD Professor of Agronomy University of California Davis, California NEW YORK • LONDON, John Wiley & Sons, Inc. ^55 \°\(oO SECOND PRINTING, JUNE, 1964 Copyright © 1960 by John Wiley & Sons, Inc. All rights reserved. This book or any part thereof must not be reproduced in any form without the written permission of the publisher. Library of Congress Catalog Card Number: 60-14240 Printed in the United States of America Preface This book has been written primarily for undergraduate students of agriculture. It has been my experience that students of agriculture, whether or not they intend to pursue careers in plant breeding, prefer instruction based on principles rather than on breeding procedures related to specific crops. At the same time, principles cannot be taught in a vacuum, as their importance and applicability may not be appre¬ ciated by those with little prior knowledge of breeding methods or problems. In preparing Principles of Plant Breeding, therefore, the goal was set to produce a textbook which, although placing principles foremost, would also provide specific examples in order to avoid abstract¬ ness. Since a textbook of plant breeding obviously cannot encompass all of agriculture, it was necessary to assume the general acquaintance of the reader with agricultural practices and problems. To achieve this goal required that the organization of Principles of Plant Breeding should depart from tradition in two respects. First, it was assumed that the student possessed a background in genetics equivalent to that obtained from a course of instruction based on one of the standard textbooks in that field. The elementary facts and principles of genetics are therefore not considered. Instead, certain aspects of inheritance are developed to a level beyond that generally attempted in a first course in genetics. For example, quantitative genetics, population genetics, systems of mating, heterosis, the genetics of pathogenic organisms, and several other topics have been singled out for amplification because of their importance to understanding not only principles but also practices in plant breeding. The second departure required that lesser emphasis be placed on the breeding of specific crops. This permitted bringing to the forefront the basic unity of methods used in breeding self-pollinated species on the one hand, and cross-pollinated species on the other. Examples were drawn from as many different crops as possible to widen interest. In 55930 VI PREFACE selecting examples, primary consideration was given to suitability in illustrating points at issue, and only secondary consideration was given to economic importance. The above considerations led to an organization in which the subject matter of plant breeding is divided into nine major areas (sections), each of which is further divided into a number of chapters. This detailed breakdown of topics is intended as an aid to instructors in emphasizing or omitting subject matter as appropriate to the backgrounds and interests of their students. An attempt was made to enable each sec¬ tion to stand on its own. Sections devoted primarily to principles precede sections on methods. Thus subject matter pertaining to the genetic basis of breeding self-pollinated crops is collected in Section Two, and methods of breeding these crops follow in Section Three. Sections Four and Five are concerned with the genetic basis and methods of breeding cross-pollinated species, respectively, and within Sections Six, Seven, and Eight chapters on principles come before related chap¬ ters on practices. Chapters on principles are for the most part not essential prerequisites to corresponding chapters on methods; however, they should provide for better understanding and greater insight if they are studied prior to or in conjunction with the sections on methods. The most difficult problem encountered arose in connection with the important subjects of biometry and the design of experiments. Since the knowledge of these subjects required of students of plant breeding is too extensive to be acquired as a mere adjunct to a course in plant breeding, the trend is to require students to take them as prerequisites to plant breeding. Moreover, there are several excellent books which cover the biometrical background essential to plant breeding. It was therefore thought redundant to include biometry and experimental design here. A few words on the way this book might be used may be helpful. Sections One, Three, and Five, together with Chapters 27, 32, 34, 35, and 36, provide elementary coverage of the subject matter included in practically every general course in plant breeding. They might serve as the basis for a one-quarter course concerned primarily with practices. Supplementation from chapters devoted primarily to principles should be possible in more rigorous one-quarter courses or in courses given over a full semester. The entire book could serve as the basis for a two- semester course. Special attention is directed to Chapters 9, 10, 15, 16, 17, and 19, which may be too difficult for some undergraduate students. These chapters were included as a challenge to undergraduates with special interest in plant breeding, and to graduate students taking their first course in the subject.