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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
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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.
