Development of a highly regenerable elite Acala cotton (Gossypium hirsutum cv. Maxxa) – a step towards genotype-independent regeneration

Abstract

A step towards genotype-independent regeneration of cotton (Gossypium hirsutum L.) was achieved by selection for regeneration potential (RG) in commercial seed of elite cultivars. A callus induction medium (MCIM) empirically determined for the cultivar `Maxxa' paved the way for RG selection among individual genotypic variants within a cultivar. MCIM consists of a basal Murashige-Skoog medium, supplemented with a unique combination of two synthetic auxins. Hypocotyl explants of `Coker 312', `Maxxa' and `Riata' seedlings cultured on MCIM successfully produced a high quality, friable callus as defined by its color, texture, size, and organization. Based on the number of fertile plants regenerated on a per seedling basis, RG was estimated as 17.4%, 44.4% and 80% in Acala cotton cultivars `Maxxa', `Ultima', and `Riata', respectively. The high RG of the cultivar Riata, a Round-up Ready® transgenic cultivar in a Maxxa genetic background, is likely due to additional RG alleles introgressed from the transgenic parent. Genotypic differences between cultivars for RG was reflected by the need for supplemental kinetin to efficiently regenerate `Ultima' plantlets via somatic embryogenesis. RG selection pressure through two cycles of selection resulted in development of advanced highly regenerable `Max-R' lines in an elite genetic background with immediate potential as suitable germplasm for breeding and biotechnology applications. Based on the results presented here, strategies for genotype-independent transformation and regeneration of cotton are proposed that integrate selection and introgression of regeneration potential in improvement programs.