Somatic hybridization in Petunia : Part 2: heteroplasmic state in somatic hybrids followed by cytoplasmic segregation into male sterile and male fertile lines

Genetic transfer in plants through interspecific protoplast fusion

Protoplasts of sexually incompatible species have been fused and in some combinations have given rise to somatic hybrid plants. Partial elimination of parental chromosomes from either species is common in such hybrids, but total chromosome loss has generally occurred only with phylogenetically unrelated pairings. Genetic function of one parent may be retained despite a complete loss of its chromosomes, suggesting that genetic introgression is possible in the absence of complete donor chromosomes. A model interspecific combination for such studies is the potato-tomato somatic hybrid for which numerous phenotypes and karyotypes are encountered at the outset, with a broader range observed in the second somatic generation.

A theoretical model for quantitatively inherited traits influenced by nuclear-cytoplasmic interactions

Cytoplasmic genes of crop species exhibit non-Mendelian inheritance and affect quantitative traits such as biomass and grain yield. Photosynthesis and respiration are physiological processes responsible, in part, for the expression of such quantitative traits and are regulated by enzymes encoded in both the cytoplasm and nucleus. Cytoplasmic genes are located in the chloroplast and mitochondrial genomes. Unlike the nuclear genome, the cytoplasmic genomes consist of single, circular, double-stranded molecules of DNA, and in many crop species, the cytoplasmic genomes are inherited solely through the maternal parent. Maternal inheritance of cytoplasmic genomes and Mendelian inheritance of the nuclear genome were used to model the genotypic value of an individual. The model then was utilized to derive genetic variances and covariances for a random-mating population. Finally, the use of reciprocal mating designs to estimate variance components was investigated.

Reciprocal transfer of male sterile and normal plasmons in Petunia

The goal in this experiment was to achieve direct plasmon transfer via cell fusion. Two lines were used - a normal fertile line of P. hybrida, and a cytoplasmic male sterile (cms) line with the nuclear background of P. parodii. Two plants phenotypically similar to the original male sterile line were developed from protoplasts, but instead of being cms they were male fertile. On the other hand, two plants typical of the original normal line developed from protoplasts, but they were cms instead of fertile. Chromosome counts were done and in all cases the expected diploid number (=14) was found. Genetic analysis showed that sorting out of cms and fertile segregants was evident in the first and second backcross of the cms cybrids. The fertile type cybrids were stable fertile for several generations of selfing and proper backcrossing. These results are discussed in the light of an earlier fusion experiment in which these two parental lines were involved.