Inheritance of competencies for leaf disc regeneration, anther culture, and protoplast culture in Solanum phureja and correlations among them

Abstract

Competence for leaf disc regeneration, anther culture, and protoplast culture was tested in the parental, F₁, and F₂ generations of a diploid cultivated primitive potato, S. phureja (2n=2x=24). The parental pair consisted of AM3-8, an anther culture derived homozygous diploid, and NBP2, a heterozygous, field selected line. AM3-8 produced embryos in anther culture, and shoots on cultured leaf discs, but its cells did not divide after protoplast isolation. Cells of NBP2 divided to form calli and shoots in protoplast culture, but the clone did not respond to anther culture or leaf disc regeneration. All the individual plants in the F₁ generation were responsive to both anther culture and protoplast culture; however, there was segregation for the ability to regenerate shoots from leaf discs. The F₂ population, the result of a sib-cross, segregated for all three tissue culture competencies. Segregation data fit a one gene model for anther culture competence with the homozygous dominant genotype expressing the highest response, the heterozygous resulting in a marginal response, and the homozygous recessive resulting in no response. A two-gene model applied to the protoplast culture data, with a dominant allele at both loci required for division to occur after protoplast isolation. Leaf disc regeneration data could only be explained by a two gene model with recessive alleles at each locus required for the highest response, a dominant allele at either of the loci resulting in a marginal response, and dominant alleles at both loci resulting in no response. No significant correlation was found among these traits, implying three separate genetic mechanisms which segregate independently.

Several temperature regimes were used in an attempt to enhance caulogenesis following protoplast isolation during the p-callus growth and regeneration phase of a single F₂ clone from this S. phureja population. Each of eight treatments was applied to 120 p-calli in six replications of 20 each. Shoot regeneration was scored at 94, 105, 121, and 131 days after protoplast isolation. P-calli cultured at 30°C days and 20°C nights produced significantly more shoots than those cultured at a constant 25°C. Therefore, the standard 25°C used for p-calli regeneration in potato may not be optimal; elevated temperatures or simply a diurnal temperature fluctuation may enhance morphogenesis.