Characterization of eleven monosomic alien addition lines added from Gossypium anomalum to Gossypium hirsutum using improved GISH and SSR markers

Cotton is the leading natural textile fiber crop in the world. Approximately 5 % of the world’s arable land is used for cotton planting, generating about $630.6 billion in 2011 [1]. Cotton belongs to the Gossypium genus of Malvaceae, which contains five tetraploid species (2n?=?4×?=?52, AADD genome) and approximately 45 diploid species (eight genomes from A to G and K, 2n?=?2×?=?26) [2]. Upland cotton (G. hirsutum) is the most widely cultivated species and its production accounts for over 95% of the world’s cotton production [3]. During the development of its cultivars, cotton has been subjected to long-term artificial selection, which narrowed its genetic base and gave rise to several difficulties in breeding. Cotton breeders face a scarcity of genetically diverse resources, therefore expanding the genetic base of cotton cultivars is imperative. Wild or untapped species have many excellent characteristics and contain abundant desirable genes, which have yet to be unlocked by pre-breeding. G. anomalum (2n?=?2×?=?26, BB genome) which is native to Africa, mainly Angola and Namibia [2], has the favorable characteristics of drought tolerance and resistance to diseases (cotton wilt, angular leaf spot) and insect pests (springtails, aphids): more importantly, it also possesses genes with the potential to produce high quality fibers (good fiber strength and fineness) [4] and cytoplasmic male sterility [5–7]. However, it is difficult to transfer these desirable genes into cultivated cotton through conventional breeding methods due to the isolation of wild species from cultivated species, which limits chromosome pairing and genetic recombination.

Monosomic alien addition lines (MAALs) contain only one alien chromosome in addition to the receptor background chromosomes. MAALs can be used as a bridge to transfer desired genes from wild species into G. hirsutum [8]. Over the past two decades, MAALs have been widely available for numerous crops [9], and these can be used for effectively identifying favorable genes in wild species, allowing for more accurate and faster transfer of such genes to create introgression lines, the effect of specific alien chromosomes to be examined, homeologies with chromosomes of cultivated species to be compared [10, 11], and physical maps of specific chromosomes to be constructed [12]. In cotton, however, the high number and smaller size of the chromosomes has resulted in difficulties in discriminating chromosomes from wild species in cultivated cotton background, therefore the development of cotton MAALs has lagged far behind many other crops. No set of cotton MAALs was reported until cotton molecular genetic maps were constructed and a genomic in situ hybridization (GISH) technique for cotton was developed. Previously, only one complete set of G. hirsutum-G. australe MAALs had been developed using simple sequence repeat (SSR) markers and GISH [9, 13, 14]. Two G. hirsutum-G. somalense MAALs and several G. hirsutum-G. sturtianum MAALs have also been obtained [11, 15].

In this study, the G. hirsutum-G. anomalum hexaploid was used as a maternal parent in the continuous backcrossing with upland cotton (recipient parent, G. hirsutum acc. TM-1), and eleven MAALs were isolated using GISH and SSR markers. These MAALs may be useful for mining and transferring favorable genes from G. anomalum into G. hirsutum on a genome-wide scale, mapping genes on chromosomes, analyzing genome structure and evolution, and micro-cloning for chromosome-specific library construction.