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.

Quan Liu,Baoliang Zhou,Jinjin Chen,Yingying Wang,Yu Chen,Tianzhen Zhang,Jean-Marc Lacape

doi:10.1371/journal.pone.0123209

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.

Highlights

The genus Gossypium comprises 50 species, including four cultivated cotton species, i.e., two diploids (G. arboreum, G. herbaceum, 2n = 26) and two tetraploids (G. hirsutum, G. barbadense), as well as 46 wild species [1]
The results demonstrate that the chromosome complement of the branch from this hybrid plant could be doubled to the tetraploid level (2n = 4x = A1A1G2G2 = 52) and the interspecific tetraploid hybrid had partial fertility
The transfer of genes of interest from wild species has played an important role in cotton breeding, and great progress has been made in the introgression of desirable traits such as superior fiber quality and disease resistance [22,23,31]

Summary

Introduction

The existing genetic base of cotton should be broadened to adapt to various adverse conditions including biotic and abiotic stress These wild species are short-fibered or lintless, they have a number of desirable traits, such as fiber quality and resistance to salt, heat, drought, insects and diseases [10,11,12]. A wild diploid cotton species (2n = 2x = 26, G2G2) (with short brownish straightly spreading fibers) that is native to Australia, 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 source of food and feed for human and animal consumption, resistance to pest insects (aphids and mites) and diseases (Fusarium and Verticillium wilt) and tolerance to abiotic stress (drought); these traits would be useful if transferred into the most important tetraploid cultivated species, G. hirsutum L. There are three strategies that could be used to simultaneously introduce desirable genes from these two species into cultivated tetraploid cotton

Methods

Results

Conclusion