Exploring the induction of doubled haploids in cassava through gynogenesis

Production and use of double haploids is important for attainment of systematic genetic gains, and indeed several plant breeding programmes have benefited from it.  Gynogenesis, the in vitro culture of unfertilized ovules and/or embryos has specifically been exploited in several economically important crops but not cassava. In this study, we examined possibilities of generating doubled haploids (DH) in cassava through gynogenesis, by bagging female flowers of selected varieties to prevent pollination. A total of 2,466 flowers across 32 elite cassava varieties were bagged for a period of one-to-three days. Early embryo rescue and ovule culture were done at 7 to 42 days after anthesis. Consequently, 517 fruits (21%) were harvested and dissected to obtain 97 seeds from which 47 unique embryos and 18 callus lines were obtained in vitro. Only six of the rescued embryos (12.8%) regenerated into plantlets. Upon undertaking ploidy analysis and single nucleotide polymorphism (SNP) genotyping, it was established that all samples analyzed (regenerated plants and calli) were diploid. SNP genotyping revealed increased homozygosity (up to 85.7%), but no doubled haploids were noticed. The knowledge generated is a significant contribution towards understanding cassava flowering biology and thus a foundation to on-going efforts towards developing protocols for generation of cassava DH. Key words: Anthesis, embryo rescue, gynogenesis, homozygosity, ploidy.