Carolyn Leach; Oliver Mayo:

Outbreeding Mechanisms in Flowering Plants

An evolutionary perspective from Darwin onwards

2005. VIII, 147 pages, 20 figures, 28 tables, 14x21cm, 340 g
Language: English

ISBN 978-3-443-50029-0, paperback, price: 24.00 €

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Abstract top ↑

In this book both the fitness effects of different breeding systems and plant outbreeding mechanisms, in particular self-incompatibility in all its variety, are reviewed for the first time.

The integrating factor is Charles Darwin, who with several Central European scientists initiated the modern investigation of both topics. The historical content is designed to demonstrate the development of understanding, the lineage of concepts and lines of investigation. This presentation of the basic historical background permits the incorporation of many detailed mechanisms into this short book.

The authors have condensed hundreds of references very substantially in order to make clear the strong associations between breeding system and fitness. Particular attention is focussed on major unsolved problems, especially the origin of self-incompatibility and the origin of diversity within these systems.

The envisaged readership encompasses academics, research students (from the end of the first degree upwards) and research workers in the plant sciences.

Review: New Zealand Journal of Botany, 2006, Vol. 44, p. 107-108 top ↑

This small volume, just over 100 pages of text in A5 format, provides a somewhat different approach to that taken by several other texts that deal with similar topics, such as Richards (1997) and de Nettancourt (2001). It aims to reevaluate some of Darwin’s observation on plant reproductive biology in the light of modern ideas of population genetics and using statistical techniques, genetics being absent from Darwin’s thoughts and observations on plant reproduction. Although the title suggests that all outbreeding mechanisms in plants will be covered, it is somewhat misleading as the main focus is very much on self-incompatibility systems. Topics such as monoecy, dioecy, and gynodioecy are confined to just five or so pages at the end of the book and consequently readers seeking information on these systems will need to look elsewhere. From the New Zealand perspective, where there is a flora that demonstrates a high frequency of dioecism and other examples of the separation of sexes into different plants or flowers, this is a bit disappointing.

There are three main chapters to the book in addition to a brief introductory one, and a short summary of research suggestions or priorities at the end. The first of these chapters contains a reevaluation of Darwin’s study on inbreeding in Ipomea purpurea (called convolvulus by the authors) and this is followed by a section on the genetics of inbreeding depression and its converse, heterosis, and concludes that inbreeding depression is fairly universal when normally outcrossing species are inbred. This chapter, and the others that follow, is characterised by bringing together information from a variety of sources and contains a useful compilation of levels of heterozygosity in relation to breeding system in a variety of plants. The table is by no means exhaustive, but provides a good start for someone wanting some initial information and insights.

The next chapter, which is called ``Means of Fertilisation'', is more about pollination ecology and the coevolution of plant and pollinator and there is no real discussion of fertilisation as such. Darwin’s observations on orchids are briefly reviewed and a table of common plant adaptations to different types or groups of pollinators is followed by a brief discussion on pollen competition between self and non-self pollen tubes in the style. There is also an interesting discussion on the relationship between the duration of flowering and reproductive success.

Chapter 4, ``Outbreeding Mechanisms'', makes up approximately two thirds of the book. It begins with a discussion of the origins of self-incompatibility that introduces a raft of ideas, such as the ABC model for the genetic control of flower development, whose relationship to the origins of self-incompatibility are at times difficult to follow. The clear evidence for very different molecular bases of recognition of self and non-self pollen between sporophytic and gametophytic self-incompatibility systems, and even differences between gametophytic systems (Solanaceae and Papaveraceae, for example), would appear to argue strongly against a single origin of self-incompatibility. Whether interspecific recognition evolved into intraspecific recognition of self is unclear at present but this seems unlikely given the multitude of different mechanisms utilised by plants to prevent interspecific hybridisation. A similar diversity of ideas brought together in a somewhat confused arrangement also characterises the sections that deal with the evolution and mechanisms of self-incompatibility. I think it would have been very useful to take a phylogenetic approach using the well-developed angiosperm phylogenetic tree (APGII 2003) to the elucidation of the possible evolutionary relationships of the different types of self-incompatibility systems. This would show that gametophytic and sporophytic systems with one or several ``S'' loci are widely distributed and the most parsimonious explanation is that they have evolved independently. The widespread recognition that all angiosperms are probably paleopolyploid also runs counter to the suggestion that self-incompatibility systems have probably evolved at the diploid level (page 44). This (paleopolyploidy) needs to be taken into account when single gene versus multigene systems are discussed as polyploidy provides duplicate genes for evolutionary experimentation. Nevertheless, there are lots of very interesting and stimulating ideas discussed in this chapter that help to highlight many areas where further investigation is needed.

My main criticism of this book is that it is not particularly reader friendly and in many places quite a lot of background information is needed to understand what is being discussed. Abbreviations are introduced without a definition or a glossary being provided and in some of the tables the contents of columns under particular heading are difficult to understand. An example of this is table 7, a useful table that shows levels of heterozygosity in relation to plant breeding system. However, under the heading ``Breeding System'' we find annual for Corrigiola litoralis, not a breeding system by any definition, and SSI for Brassica rapa. The initiated would know that SSI stands for sporophytic self-incompatibility but sporophytic self-incompatibility is not defined before this table in the text. It could be argued that any plant science graduate should know what SSI means, though I seriously doubt this is so, but there are numerous other examples that to me appear much more obscure. For example, in figure 6 there is a SQUA clade, a DEF clade, an Angiosperm AG subclade, etc. I don’t know what these abbreviations mean. I could go and look at the original source (given in the figure caption), but much better would have been a bit more explanation in either text or figure legend. The same can be said for figure 7, an angiosperm phylogeny obtained from SRNase sequences where a series of families (several incorrectly spelt) are followed by letters such as G, G+, S. No explanation is provided anywhere about what these letters mean. There are also quite a lot of typographical errors scattered throughout the book; headings to table columns are incorrectly placed, words have letters missing, and many incorrectly spelt words are present in both text and tables.

Although this book is not an easy read I would recommend it strongly to anyone interested in plant breeding systems as its approach is novel and it contains much of interest. However, it is not an exhaustive text and the two books quoted above would need to be used in conjunction by the uninitiated.

B. G. MURRAY (School of Biological Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand)

New Zealnd Journal of Botany, 2006, Vol. 44, p. 107-108

Bespr.: Berichte der Bayerischen Botanischen Gesellschaft 2007 top ↑

Dieses ausgezeichnete kleine Buch resultiert aus der Zusammenarbeit zweier australischer Populationsgenetiker mit langjähriger Unterrichts-Erfahrung und Interesse an Didaktik. Entsprechend den Forschungsschwerpunkten der Autoren – sie haben wichtige Arbeiten zur Genetik der Selbstinkompatibilität veröffentlicht, und Mayo ist zudem Autor zweier pflanzengenetischer Lehrbücher – liegt der Schwerpunkt des Buches auf der quantitativen Genetik von Inzuchtdepression und den genetischen Mechanismen der Selbstinkompatibilität. Das Buch besticht besonders durch die Breite der von den Autoren überschauten Literatur, von klassisch-reproduktionsbiologischen Arbeiten über populationsgenetische zu molekularbiologischen; die neuesten zitierten Publikationen sind von 2004.

Jedes der drei Kapitel beginnt mit Fragen, die bereits Darwin (1876, 1877) durch seine Kreuzungsversuche an Pflanzen zu beantworten suchte, und zum Teil werden Darwins Ergebnisse mit der statistischen Auswertung, die zu seiner Zeit noch nicht möglich war, nachanalysiert. Ein interessanter Appendix listet die ca. 300 Pflanzenarten auf, mit denen Darwin experimentell arbeitete und zitiert zu jeder neuere Literatur zu ihrem Geschlechts- und Inkompatibilitätssystem (soweit seither untersucht). Der didaktische Trick, immer wieder Darwins Ideen und Schwierigkeiten anzuführen, macht den Text ausgesprochen ansprechend, und immer wieder staunt man auch über „Darwin’s views, untrammelled by genetical knowledge, but informed by unparalleled evolutionary insight ...“ (S. 46). Die wichtigsten Inkompatibilitätssysteme (gametophytische, sporophytische, homomorphe und heteromorphe Inkompatibilität) werden ausführlich und von der populationsgenetischen bis zur molekularen Ebene dargestellt. Ich kenne keine bessere knappe Darstellung. Das Buch ist sehr schön produziert und angesichts des geringen Preises voll und ganz zu empfehlen.

S. Renner

Berichte der Bayerischen Botanischen Gesellschaft

Contents top ↑

Table of Contents

Preface VII
1. Introduction 1
2. The effects of inbreeding and outbreeding 3
2.1 What Darwin wanted to achieve 3
2.2 What hampered Darwin 4
2.3 Darwin?s experimental designs 4
2.4 Inheritance 8
2.5 What Darwin achieved 8
2.6 Inbreeding 9
2.6.1 Darwin?s evidence 9
2.6.2 Current evidence 10
2.7 Genetics of inbreeding depression 11
3. Means of fertilisation 24
3.1 Darwin?s evide . 24
3.2 Current evidence 25
4. Outbreeding mechanisms 31
4.1 Origin of self-incompatibility 31
4.2 Evolution of homomorphic systems 44
4.2.1 Evolution of gametophytic systems 51 Single locus 51 Multiple locus 62 Breakdown of gametophytic systems 66
4.2.2 Evolution of sporophytic systems 68 Single locus 71 Multiple locus 78 Breakdown of sporophytic systems 79
4.2.3 The possibility of polygenic systems 80
4.3 Evolution of heteromorphic systems 83
4.3.1 Mechanism of heteromorphic self-incompatibility 86
4.3.2 Breakdown of heteromorphic systems 91
4.3.3 Enantiomorphy 95
4.3.4 Monoecy, dioecy, gynodioecy and androdioecy 95 Genetical determination of dioecy 97
4.4 Comparison of systems 99
5. Some possibilities for research 101
Appendix 104
References 113
Author Index 135
Genera and species Index 144
Topic Index 146