A New Synthetic Allotetraploid (A1A1G2G2) between Gossypium herbaceum and G. australe: Bridging for Simultaneously Transferring Favorable Genes from These Two Diploid Species into Upland Cotton

Abstract

Gossypium herbaceum, a cultivated diploid cotton species (2n = 2x = 26, A1A1), has favorable traits such as excellent drought tolerance and resistance to sucking insects and leaf curl virus. G. australe, a wild diploid cotton species (2n = 2x = 26, G2G2), possesses numerous economically valuable characteristics such as delayed pigment gland morphogenesis (which is conducive to the production of seeds with very low levels of gossypol as a potential food source for humans and animals) and resistance to insects, wilt diseases and abiotic stress. Creating synthetic allotetraploid cotton from these two species would lay the foundation for simultaneously transferring favorable genes into cultivated tetraploid cotton. Here, we crossed G. herbaceum (as the maternal parent) with G. australe to produce an F1 interspecific hybrid and doubled its chromosome complement with colchicine, successfully generating a synthetic tetraploid. The obtained tetraploid was confirmed by morphology, cytology and molecular markers and then self-pollinated. The S1 seedlings derived from this tetraploid gradually became flavescent after emergence of the fifth true leaf, but they were rescued by grafting and produced S2 seeds. The rescued S1 plants were partially fertile due to the existence of univalents at Metaphase I of meiosis, leading to the formation of unbalanced, nonviable gametes lacking complete sets of chromosomes. The S2 plants grew well and no flavescence was observed, implying that interspecific incompatibility, to some extent, had been alleviated in the S2 generation. The synthetic allotetraploid will be quite useful for polyploidy evolutionary studies and as a bridge for transferring favorable genes from these two diploid species into Upland cotton through hybridization.

A New Sythetic Hybrid (A1D5) between Gossypium herbaceum and G. raimondii and Its Morphological, Cytogenetic, Molecular Characterization

“…Anthers at different development stages were collected from immature flower buds of the hybrid plants and fixed in freshly prepared Carnoy's fluid (ethanol: acetic acid = 3:1 v/v) [ 11 ] immediately. After 24 hours, the fixed anthers were transferred to 70% ethanol and stored at 4°C for cytogenetic observation.…”

“…herbaceum × G . australe (G2) [ 11 ], etc. Currently, it is well accepted that hybridization plays a major role in cotton plant breeding due to the increase of the genetic diversity available and the production of new genotypes [ 12 ].…”

Genome sequencing of the Australian wild diploid species Gossypium australe highlights disease resistance and delayed gland morphogenesis

“…To date, cotton genomics researchers have developed high‐quality reference sequences for 2 diploid groups, as well as allotetraploid cottons (‘A‐genome’, ‘D‐genome’ and ‘AD‐genome’ clade) including 3 cultivated species (AA, G. arboreum , AADD, G. hirsutum and G. barbadense ) and 1 wild ancestor species (DD, G. raimondii ) (Du et al ., ; Hu et al ., ; Li et al ., , ; Paterson et al ., ; Wang et al ., , ; Zhang et al ., ). Comparatively little research attention has been focused on Australian cotton species such as G. australe (with its ‘GG’ genome in cotton genomics nomenclature) (Chen et al ., ; Liu et al ., ; Wang et al ., ).…”

Wild Relatives of Maize, Rice, Cotton, and Soybean: Treasure Troves for Tolerance to Biotic and Abiotic Stresses

“…G. australe , a wild G-genome species possesses resistance to Fusarium wilt and Verticillium wilt diseases apart from other economically important traits such as resistance to aphids and mites. G. herbaceum , a cultivated diploid species (A-genome), has resistance to leaf curl virus along with other favorable traits including tolerance to sucking pests and drought tolerance (Liu Q. et al, 2015 ). Recently, a novel synthetic allotetraploid (A 1 A 1 G 1 G 1 ) was developed from two diploid species and capable to lay the foundation for transferring favorable alleles into Upland cotton (Liu Q. et al, 2015 ).…”

“…G. herbaceum , a cultivated diploid species (A-genome), has resistance to leaf curl virus along with other favorable traits including tolerance to sucking pests and drought tolerance (Liu Q. et al, 2015 ). Recently, a novel synthetic allotetraploid (A 1 A 1 G 1 G 1 ) was developed from two diploid species and capable to lay the foundation for transferring favorable alleles into Upland cotton (Liu Q. et al, 2015 ). It was reported that throughout Australia no Fusarium spores were isolated from G. sturtianum stems suggesting that this species might possess Fusarium resistance (Wang et al, 2004 ), whereas G. bickii showed higher affinity with the pathogen (McFadden et al, 2004 ).…”