INDEPENDENT SEGREGATION OF THE PLASTID GENOME AND CYTOPLASMIC MALE-STERILITY IN PETUNIA SOMATIC HYBRIDS

The chloroplast genomes of 3 sets of Petunia somatic hybrids [P. hybrida, P. parodii] were analyzed to examine the relationship between chloroplast DNA (cpDNA) composition and cytoplasmic male sterility (CMS). Chloroplast genomes of somatic hybrid plants were identified either by restriction and electrophoresis of purified cpDNA or by hybridization of total DNA digests with cloned cpDNA probes that distinguish the parental genomes. The chloroplast genomes of a set of 7 somatic hybrids derived from the fusion of Petunia CMS line 2423 and fertile line 3699 were analyzed. All 7 plants were fertile, and all exhibited the cpDNA restriction pattern of the sterile cytoplasm. Similarly, 4 fertile somatic hybrids derived from the fusion of CMS line 3688 and fertile line 3677 were found to contain the CMS chloroplast genome. The cpDNA compositions of 4 fertile and 2 sterile somatic hybrids derived from the fusion of CMS line 3688 and fertile line 3704 were determined by restriction analysis of purified cpDNA; all 6 plants exhibited the cpDNA restriction pattern of line 3704. Thus, the CMS phenotype segregates independently of the chloroplast genome in Petunia somatic hybrids, indicating that CMS in Petunia is not specified by the chloroplast genome.