Cotton Breeding

Abstract

Cotton (Gossypium spp.) is an economically important cash crop grown in more than 90 countries in tropical, sub-tropical and temperate climate for its fibre, oil and protein. Cotton belongs to the genus Gossypium that contains 50 species, of which 43 are diploids (2n = 26) and seven tetraploids (2n = 4x = 52). The diploid species are grouped in seven genomes designated as A–G and K. The tetraploid species with AADD genome originated from natural crossing involving cultivated diploid G. herbaceum (A1) and wild diploid species G. raimondii (D5), followed by polyploidization. Cultivated cotton has a narrow genetic base which is becoming a hindrance in sustaining cotton productivity worldwide. Broadening the genetic base of cultivated cotton by mobilizing the useful genetic variations from diverse exotic accessions, races of cultivated species and wild accessions requires to be the top priority. The use of molecular markers and advances in sequencing technology has resulted in the development of huge genomic resources that includes molecular markers, several linkage maps and more than 6497 quantitative trait loci (QTL) representing more than 30 agronomically important traits mapped on specific chromosomes. To facilitate high-throughput genotyping of the breeding populations, SNP arrays have been developed and extensively used for genetic mapping and marker-assisted breeding programmes. The last decade witnessed complete genome sequencing and resequencing of cultivated and more than a dozen wild species of cotton. Whole cotton genome sequence data provides a major source of candidate genes with potential for genetic improvement of cotton quality and productivity. Insect- and herbicide-resistant transgenics are under cultivation across the cotton-growing countries. Genotype-dependent genetic transformation is known in cotton. Versatile and robust somatic regeneration protocol suiting to a diverse set of genotypes would facilitate transgenic development for economic traits. Precision genome editing tool CRISPR/Cas9 and further refinement in the technology has demonstrated successful simultaneous multiple gene-targeted mutagenesis in several crops including cotton. This technology holds promise to develop transgene-free edited plants for economic, quality, resistance and adaptation traits in cotton. This chapter dwells upon all broad aspects of conventional breeding and molecular tools for cotton improvement, present status and perspectives for cotton production sustainability.KeywordsCottonGenetic resourcesBreeding methodsDNA markersMarker-assisted selection (MAS)Genome-wide association studies (GWAS)Genotyping by sequencing (GBS)Transgenics, Genome editing