Genetics and in vitro culture of somatic embryogenesis in Gossypium hirsutum L

Experiments were conducted to examine various parameters of somatic embryogenesis from mature-petiole callus tissue of Gossvpium hirsutum L.

Experiment 1. Petioles from Acala SJ-5, Coker 312, Paymaster 303, Tl, T25 and T169 plants were cultured on three modified MS media to induce embryogenesis. Callus formed from all explants on all media, though embryogenesis was observed only on T25 and Coker 312 tissue.

Experiment 2. Acala SJ-5, Coker 312, Paymaster 303, Tl, T25 and T169 plants were tested for ability to undergo somatic embryogenesis in parental, F]_, F2 and BC-L generations. Explants were cultured on modified MS medium. plus 4.0 mg/1 NAA and 1.0 mg/1 Kn. Segregation for embryogenesis was observed in all generations. More embryogenic cultures and more embryos/embryogenic culture were produced from plants with a T25 lineage than with Coker 312 lineage. The action of at least two genes is proposed. Use of T25 as an embryogenesis donor parent is suggested.

Experiment 3. Explants were cultured on modified MS medium supplemented with BA, 2iP or Kn in combination with NAA or 2,4-D at various levels. BA -I- 2,4-D and Kn + 2,4-D produced negligible embryogenesis. Embryogenesis was induced by NAA + Kn and NAA + BA, but only at low levels of cytokinin. Embryogenic callus was initiated by NAA with no cytokinin and 2iP with no auxin. These results suggest two pathways of embryogenesis induction, one through the action of cytokinin, the other by the action of auxin. The optimum growth regulator combination was 1.0-3.0 mg/1 NAA + 0.1-1.0 mg/1 2iP.

Experiment 4. Explants from Coker 312 and T25 were cultured on two modified MS media. Medium A contained 4.0 mg/1 NAA and 1.0 mg/1 Kn. Medixim B contained 0.1 mg/1 2,4-D and 0.1 mg/1 Kn. After six weeks, callus from each explant was divided, one portion was placed in liquid proliferation medium (modified MS, no growth regulators, no Gelrite), the other on semi-solid proliferation medium (modified MS, no growth regulators). Embryos were counted after eight weeks. Percentage of explants forming callus was influenced by genotype/initiation medium combination. Initiation medium x genotype interactions for embryo production were detected. Significantly more embryos were produced in liquid proliferation medium (227.3 embryos/culture) than on semi-solid proliferation medixim (134.6 embryos/culture).