1 College of Grassland Science and Technology, Sichuan
Agricultural University, Wenjiang 611100, Chengdu China;
pengyanlee@163.com
2 Guangdong Technology Research Center for Marine
Algal Bioengineering, Guangdong Key, Laboratory of Plant Epigenetics,
College of Life Sciences and Oceanography, Shenzhen University,
Shenzhen 518055, China; anwar_uaar@yahoo.com
* Correspondence: m.zafarsindhu@hotmail.com (M.Z.I.)
Abstract: Interspecific hybridization has contributed
significantly to land diversity, species evolution, and crops’
domestication, including upland cotton, the cultivated form ofGossypium hirsutum . Being the world’s most important fiber crop
species, Gossypium hirsutum belongs to the allotetraploid
Gossypium consisting of six additional tetraploid species. The lint
fiber evolved once in diploid parent A-genome species in theGossypium ’s history and passed on during hybridization of the
A-genome with the D-genome and was maintained in subsequent evolution.
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. Crossing with G.
barbadense has resulted in the development of multiple genetic lines in
contemporary upland cotton. However, in later-generation hybrids betweenG. hirsutum and other polyploid species, reproductive barriers
such as reduced fertility, segregation distortion, and hybrid breakdown
are frequently observed, complicating the task of introgressing new,
stably inherited allelic variation from inter-specific hybridization.
Recent efforts in molecular genetics 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.
Keywords: interspecific hybridization; Gossypium
hirsutum; crop improvement; fiber quality; polyploidization;
introgressive breeding
1. Introduction
Cotton is a food and fiber plant contributing to humanity’s fundamental
requirements. Cotton fiber, in the form of textile objects, contributes
significantly to the comfort, style, and culture of human society.
Despite its lack of appeal as a food, cotton is a primary source of
vegetable oil, which is used extensively in meals such as baking and
frying fats, mayonnaise, margarine, and snack food. Following oil
extraction, the seed by-product is used as a raw material in animal
feed, fertilizer, and paper. Because of its flexibility, cotton is one
of the most important field crops in the world. According to the
International Cotton Advisory Committee (ICAC), which collects data on
global cotton production, consumption, and commerce, cotton is grown on
36 million hectares in over 100 countries
[1]. The top five
cotton-producing countries are China, India, the United States,
Pakistan, and Brazil, which account for around two-thirds of worldwide
cotton production [2]. Cotton has
become the most important natural fiber in the textile industry, as well
as a vital agricultural product in the global economy. The annual value
of the worldwide cotton crop is estimated to be over USD 30 billion,
with lint fiber accounting for 90% of that value
[3]. Cotton farming and
processing employ about 350 million people worldwide. Cotton’s economic
importance as a natural fiber for the global textile industry has
spurred a lot of interest in improving the crop’s inherent genetic
potential by breeding cultivars with higher biotic and abiotic
tolerance, higher lint yield, and enhanced fiber quality
[4].
Cotton’s development and progress have benefited greatly from
interspecific hybridization. Cotton remarkable as a crop in that four
distinct species of the genus Gossypium (Malvaceae) were
domesticated for lint fiber production on two separate continents
[5,6].
As a result, in the textile business, the two allotetraploid speciesG. hirsutum L. and G. barbadense L., both native to the
Americas, and the two diploid species G. arboreum L. and G.
herbaceum L., both endemic to Africa and Asia, are referred to as
“cotton.” Allotetraploid Gossypium has a single
polyploidization history, with progenitors that resemble G.
herbaceum or G. arboreum (A genome) and G. raimondii (D
genome) merging together [6]. The two allotetraploids now provide
the great majority of the world’s textile fiber, with G. hirsutumaccounting for more than 90% of worldwide cotton production
[7]. As a result, the focus of
this review will be on G. hirsutum , popularly known as “Upland”
cotton, a cultivated allotetraploid species. Other domesticated and
non-domesticated allotetraploid species, on the other hand, will be
included since they represent a vast pool of untapped genetic resources
for future genetic advancement.
2. Taxonomy of Gossypium and Origin of Gossypium hirsutum
The genus Gossypium contains around 50 species, which are distributed in
tropics and subtropics regions. Diploid Gossypium species are
categorized into eight genome groups (A–G, K) based on chromosomal
pairing affinities [8]. Despite
the fact that numerous important diversification sites have been
identified, these species collectively have a large distribution.
A-genome species are found both in Africa and Asia; B- and F-genome
species are mainly present in Africa; Arabia has E-genome species; C-,
G-, and K-genome species can be found in Australia; whereas D-genome
species can be found in Central and South America. The detailed grouping
and geographical distribution of Gossypium species are summarized
in Table 1. Although molecular phylogenetic investigations have
established a phylogenetic framework for the genus and its many genome
types, a thorough understanding of the evolutionary links between each
species remains elusive [6]. G. hirsutum and G.
barbadense , two domesticated species, plus G. tomentosum Nutt ex
Seem, G. darwinii Watt, and G. mustelinum Miers ex G.
Watt, are the five allotetraploid Gossypium species that have been
extensively recognized in the past. G. ekmanianum Wittmack, a
sixth species, was recently discovered, and a seventh was discovered
(see below). Polyploid Gossypium has a broad geographic distribution
that includes several seasonally dry subtropical and tropical parts of
the North and South American continents, mainly near coasts, as well as
numerous Caribbean and Pacific islands. As a result, these species are
commonly referred to as New World cotton. The fact that G.
darwinii (Galapagos Islands), G. ekmanianum (Hispaniola), andG. tomentosum (Hawaiian Islands) are all island endemics suggests
that these species evolved after long-distance dispersion episodes
[6,9]. The native Brazilian
cotton (Gossypium mustelinum) has never been cultivated. It is
tetraploid and may be crossed with cultivated cotton. Gossypium
mustelinum is grown in semiarid region and expanded to the coastal area
of northeast Brazil in 2018. It is cultivated in Paraiba and Pernambuco
in Brazil [10]. G.
hirsutum is native to Central America, whereas G. barbadense is
native to South America, but their ranges overlap, notably in northwest
South America and across the Caribbean. Two new species have just been
added to the allopolyploid cotton group. Based on accessions obtained in
the Dominican Republic, the species G. ekmanianum Wittm was
recently revived
[11,12].
A seventh species, Gossypium stephensii[13], has been recently
discovered in the Wake Atoll in the Pacific Ocean (Wake, Peale, and
Wilkes Islands) [13,14].G. hirsutum , G. tomentosum , G. ekmanianum, and the newly
found species form one clade; G. barbadense and G.
darwinii form a second clade; and G. mustelinum remains the
allopolyploid phylogeny’s basal clade [6]. Because of their
monophyletic origin, all seven polyploid species have two sets of 13
homoeologous chromosomes (2n = 4x = 52) and strict disomic chromosome
pairing (Kimber 1961) A-genome cytoplasm. Polyploidization occurred
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 [6]. The At- and Dt-subgenomes of the
tetraploids were provided by diploid progenitors that resemble G.
arboreum or G. herbaceum , and G. raimondii , respectively,
according to meiotic chromosomal pairing and comparative genome studies.
The progenitors of these species separated from a common ancestor 5–7
million years ago, according to DNA sequence evidence
[6,15]. Cotton’s A- and D-genome
progenitors have at least nine chromosomal rearrangements in common
[16]. Furthermore, the A-genome
contains around twice as much gametic DNA as the D-genome
[17], with the increased genome
size attributed mostly to the repetitive DNA fraction, as the quantity
of single-copy DNA in both genomes is nearly equal
[18]. Genetic mapping
[19,20]
identified the matching homoeologous chromosomes of the At- and
Dt-subgenomes, which were recently confirmed by two draft genomes
sequences [14]. In the At sub genome, direct comparisons of gene
order and synteny between the two sub genomes revealed two reciprocal
translocations between chromosomes 02/03 and 04/05, as well as multiple
probable inversions [18,19]. The tetraploid chromosomes have also
been aligned with those of their diploid progenitors, indicating that
there has been more rearrangement since polyploid development
[20,21]. Nonetheless, these
findings suggest that gene collinearity between the two subgenomes is
substantial, and that chromosomal structural rearrangement has been
minimal after allopolyploid formation. A grouping of Gossypiumspecies based on genomic diversity is shown in Table 1, and the
evolution of Gossypium species, including tetraploidGossypium species formation, is illustrated in Figure 1.
Table 1. Grouping and geographical distribution of the genusGossypium species based on genomic diversity validated by
cytogenetic data and other means.