Polyploidy and Hybridization for Crop Improvement

Annaliese S. Mason, Annaliese S. Mason

• Publisher: CRC Press
• Year: 2017
• ISBN:
  9781315352268
• Edition: 1
• Topic: Sciences biologiques
• Subtopic: Botanique

Many of our current agricultural crops are natural or agricultural hybrids (between two or more species), or polyploids (containing more than one genome or set of chromosomes). These include potato, oats, cotton, oilseed rape, wheat, strawberries, kiwifruit, banana, seedless watermelon, triticale and many others. Polyploidy and hybridization can also be used for crop improvement: for example, to introgress disease resistance from wild species into crops, to produce seedless fruits for human consumption, or even to create entirely new crop types. Some crop genera have hundreds of years of interspecific hybridization and ploidy manipulation behind them, while in other genera use of these evolutionary processes for crop improvement is still at the theoretical stage. This book brings together stories and examples by expert researchers and breeders working in diverse crop genera, and details how polyploidy and hybridization processes have shaped our current crops, how these processes have been utilized for crop improvement in the past, and how polyploidy and interspecific hybridization can be used for crop improvement in the future.

Chapter 1

Interspecific Hybridization for Upland Cotton Improvement

Peng W. Chee^1,*, Andrew H. Paterson², Joshua A. Udall³ and Jonathan F. Wendel⁴

ABSTRACT

Interspecific hybridization has been central to the evolution, domestication, and improvement of Upland cotton, the cultivated form of Gossypium hirsutum. As the world’s most important fiber crop species, Gossypium hirsutum belongs to the allotetraploid Gossypium clade that consists of six additional species. The lint fiber evolved only once in the history of Gossypium, in the ancestor diploid A-genome species, and this trait was passed on to the allopolyploid species when the A-genome united in a common nucleus with a D-genome from the other ancestor that produced no lint fibers. The domestication history of G. hirsutum involved the collection and use of lint fibers by indigenous people for the purpose of making strings and other textile products; hence, spinnable lint fibers were likely to have evolved under domestication. The geographical distribution of G. hirsutum overlaps with G. barbadense and G. mustelinum, and gene flow among these species has been documented. Therefore, the introgression of novel alleles into G. hirsutum possibly contributed to greater ecological adaptation in colonizing new habitats and providing important sources of genetic variation for artificial selection in the early domestication efforts. In modern Upland cotton, numerous germplasm lines have been developed from crossing with G. barbadense. However, reproductive barriers such as reduced fertility, segregation distortion, and hybrid breakdown are often observed in later generation hybrids between G. hirsutum and the other polyploid species, complicating the task of introgressing new, stably inherited allelic variation from inter specific hybridization. Recent efforts in molecular genetic research have provided insights into the location and effects of QTLs from wild species that are associated with traits important to cotton production. These and future research efforts will undoubtedly provide the tools that can be utilized by plant breeders to access novel genes from wild and domesticated allotetraploid Gossypium for Upland cotton improvement.

The Cotton Crop

The cotton plant is a source of both food and fiber, contributing to two basic needs of humanity. Cotton fiber in the form of textile products has contributed greatly to the comfort, style, and culture of human society. Although not commonly viewed as a food source, cotton is an important source of vegetable oil used extensively in foodstuffs such as baking and frying fats, mayonnaise, margarine, and snack food. Furthermore, after oil extraction, the seed by-product is used as raw material in livestock feed, fertilizer, and paper. This versatility has made cotton one of the most important field crops in the world.

According to the International Cotton Advisory Committee (ICAC), which collects statistics on world cotton production, consumption and trade, about 36 million hectares of cotton are planted in over 100 countries from latitudes 45°N in Ukraine to 32°S in Australia (ICAC, 2015). The top five cotton producing countries in the 2014-15 season include, in order of importance, China, India, the United States, Pakistan and Brazil, which collectively account for nearly two-thirds of the world’s cotton production. Total cotton fiber production has now reached 106 million bales, and contributes about 40% of the world fiber market (ICAC, 2015), thus making cotton the single most important natural fiber in the textile industries and a vital agricultural commodity in the global economy. The aggregate value of the world’s cotton crop is estimated to be about US$30 billion/yr, with 90% of its value residing in lint fiber. More than 350 million people are engaged in jobs related to the production and processing of cotton. The economic importance of cotton as a natural fiber for the global textile industry has fueled considerable interest in improving the inherent genetic potential of the crop through breeding for cultivars with higher levels of biotic and abiotic tolerance as well as higher lint yield and the further enhancement of fiber quality.

Interspecific hybridization has been central to the evolution of cotton, and to its improvement. As a crop, cotton is unique in that four different species in the genus Gossypium (Malvaceae) were domesticated independently on two separate continents for lint fiber production (Wendel and Cronn 2003; Wendel and Grover 2015). Therefore, the word “cotton” in the textile industry can apply equally to the two allotetraploid species G. hirsutum L. and G. barbadense L., endemic to the Americas, and the two diploid species G. arboreum L. and G. herbaceum L., endemic to Africa and Asia. Allotetraploid Gossypium trace to a single polyploidization, joining progenitors resembling G. herbaceum or G. arboreum (A genome) and G. raimondii (D genome) (Wendel and Grover, 2015). Currently, the two allotetraploids supply an overwhelming majority of the world’s textile fiber, with G. hirsutum responsible for over 90% of the total cotton production. This chapter will therefore focus on the cultivated allotetraploid species G. hirsutum, commonly referred to as “Upland” cotton. However, we will reference other domesticated and non-domesticated allotetraploid species, as they represent a vast reservoir of untapped genetic resources to sustain continued genetic improvement.

Origin and Taxonomy of Gossypium hirsutum

The genus Gossypium includes over 50 species of shrubs and small trees indigenous to the arid and semiarid tropics (Fryxell 1979; Wendel and Grover 2015). Diploid Gossypium species have 13 pairs of chromosomes (2n = 2x = 26) and are grouped into eight different genome types (A-G, K) based on chromosome pairing affinities (et al. 1984). Collectively, these species have a widespread distribution, although several primary centers of diversity are recognized. Specifically, A-genome species are found in Africa/Asia, B- and F-genome species in Africa, E-genome species in Arabia, C-, G- and K-genome species in Australia and D-genome species in Central and South America. Molecular phylogenetic analyses (Cronn et al. 2002; reviewed in Wendel and Grover 2015) have provided a phylogenetic framework for the genus and its different genome types, although the complete picture of the evolutionary relationships between each species is still not fully clear. The taxonomy of the diploid Gossypium species is described in detail by Fryxell (1979).

In comparison to the diploids, the phylogenetic history of polyploid cottons is better established (Grover et al. 2015), although new species continue to be discovered (Grover et al. 2014, and Wendel unpublished). Classically, five allotetraploid Gossypium species have been widely recognized that include the two domesticated species, G, hirsutum and G. barbadense, and three wild species, G. tomentosum Nutt ex Seem, G. darwinii Watt, and G. mustelinum Miers ex G. Watt. A sixth species, G. ekmanianum Wittmack, was recently resurrected and a seventh identified (see below). The aggregate geographic range of polyploid Gossypium encompasses many seasonally arid subtropical and tropical regions of the North and South American continents, mostly near coastlines, and extends to many islands in the Caribbean and the Pacific. Hence, these species collectively are often referred to as the New World cottons. The island endemic nature of G. darwinii (Galapagos Islands), G. ekmanianum (Hispaniola) and G. tomentosum (Hawaiian Islands) indicates that these species likely originated following long-distance dispersal events (Wendel and Cronn 2003; Wendel and Grover 2015). Gossypium mustelinum is indigenous to a small region of northeast Brazil (Wendel et al. 2009). As for the two domesticated species, G. hirsutum is indigenous to Central America and G. barbadense to South America but their ranges overlap, particularly in northwest South America and extensively in the Caribbean.

Recently, two additional species have been added to the allopolyploid cotton clade. The species G. ekmanianum Wittm. was recently resurrected (Krapovickas and Seijo 2008; Grover et al. 2014), based on accessions found in the Dominican Republic. In addition, a seventh species has been identified from the Wake Atoll in the Pacific Ocean (Wake, Peale, Wilkes Islands), Gossypium sp. Nov. (Wendel et al. unpublished data). Therefore, the most current iteration of the allopolyploid cotton phylogeny consists of seven lineages in three clades, with G. hirsutum, G. tomentosum, G. ekmanianum and the newly discovered species forming one clade, G. barbadense and G. darwinii forming a second clade, and G. mustelinum remaining the basal clade of the allopolyploid phylogeny (Wendel and Grover 2015).

All seven polyploid species have two sets of 13 homoeologous chromosomes (2n = 4x = 52) and exhibit strict disomic chromosome pairing (Kimber 1961). They all contain A-genome cytoplasm due to their monophyletic origin, with polyploidization occurring about 1-2 million years ago by transoceanic migration of an Old World (A-genome) progenitor followed by hybridization with a native New World (D-genome) progenitor (Wendel 1989; reviewed in Wendel and Grover 2015). Both meiotic chromosome pairing and comparative genome analyses have shown that the At- and Dt-subgenomes of the tetraploids were contributed by diploid progenitors that resemble G. arboreum or G. herbaceum, and G. raimondii, respectively. DNA sequence data indicates the progenitors of these species diverged from a common ancestor 5-7 million years ago (Senchina et al. 2003; Wendel and Grover 2015).

The A- and D-genome progenitors of cotton differ by at least 9 chromosomal rearrangements (Reinisch et al. 1994). Additionally, the A-genome has about twice the gametic DNA content as the D-genome (Hendrix and Stewart 2004), with the larger genome size mostly due to the repetitive DNA fraction, as the amount of single-copy DNA is almost the same in both genomes (Greever et al. 1989). The corresponding homoeologous chromosomes of the At- and Dt-subgenomes have been established by genetic mapping (Reinisch et al. 1994; Rong et al. 2004; Wang et al. 2014), and more recently verified by two draft genome sequences (Li et al. 2015; Zhang et al. 2015). Direct comparisons of gene order and synteny between the two subgenomes showed two reciprocal translocations in the At subgenome between chromosomes 02/03 and between chromosomes 04/05 as well as several possible inversions (Rong et al. 2004; Wang et al. 2014). The tetraploid chromosomes have also been aligned with those of their diploid progenitors, revealing that additional rearrangement has occurred since polyploid formation (Brubaker et al. 1999; Rong et al. 2004; Desai et al. 2006). Nonetheless, these results collectively indicate that gene colinearity is high between the two subgenomes and that chromosomal structural rearrangement has been modest following allopolyploid formation.

Domestication and “Upland” Cotton

The epidermal layer of cotton seed contains ‘linters’ or fuzz, which are short fibers that tightly adhere to the seed coat, and longer ‘lint’ fibers, which loosely adhere to the seed. The fuzz fibers represent an important source of raw material for the manufacture of paper and other industrial cellulose products. However, it is the longer, spinnable lint fibers that make cotton the world’s most important fiber crop, and these novel single-celled seed epidermal trichomes may have first attracted ancient peoples to the cotton plant. As mentioned earlier, four different Gossypium species were domesticated independently by four geographically different civilizations on two separate continents; A genome diploids G. herbaceum and G. arboreum were domesticated in Africa and Asia, and allopolyploids G. hirsutum and G. barbadense were domesticated in Central and South America (Fryxell 1979; Brubaker et al. 1999).

The domestication history of G. hirsutum is not unlike those of the other three cultivated cotton species; it is likely to have involved the collection and use of lint fibers by indigenous people for the purpose of making strings and other textile products (Brubaker et al. 1999). The long lint fiber, which has a flat convoluted ribbon structure that permits the fiber to be spun into yarn, evolved under domestication (Brubaker et al. 1999). Accordingly, wild cottons have short and coarse lint fibers tha...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Preface
• 1. Interspecific Hybridization for Upland Cotton Improvement
• 2. Allopolyploidy and Interspecific Hybridization for Wheat Improvement
• 3. Potato Breeding through Ploidy Manipulations
• 4. Polyploid Induction Techniques and Breeding Strategies in Poplar
• 5. Musa Interspecific Hybridization and Polyploidy for Breeding Banana and Plantain (Musaceae)
• 6. Strawberry (Plants in the Genus Fragaria)
• 7. The Role of Polyploidization and Interspecific Hybridization in the Breeding of Ornamental Crops
• 8. Polyploidy in Maize: The Impact of Homozygosity and Hybridity on Phenotype
• 9. Broadening the Genetic Basis for Crop Improvement: Interspecific Hybridization Within and Between Ploidy Levels in Helianthus
• 10. Crop Improvement of Phaseolus spp. Through Interspecific and Intraspecific Hybridization
• 11. Triticale
• 12. Polyploidy and Interspecific Hybridization in Cynodon, Paspalum, Pennisetum, and Zoysia
• 13. Interploid and Interspecific Hybridization for Kiwifruit Improvement
• 14. Oat Improvement and Innovation Using Wild Genetic Resources (Poaceae, Avena spp.): Elevating “Oats” to a New Level and Stature
• 15. Interspecific Hybridization of Chestnut
• 16. Use of Polyploids, Interspecific, and Intergeneric Wide Hybrids in Sugar Beet Improvement
• 17. Polyploidy in Watermelon
• 18. Optimization of Recombination in Interspecific Hybrids to Introduce New Genetic Diversity into Oilseed Rape (Brassica napus L.)
• 19. Interspecific Hybridization for Chickpea (Cicer arietinum L.) Improvement
• Index