THE CHLOROPLAST AND MITOCHONDRIAL-DNA TYPE ARE CORRELATED WITH THE NUCLEAR COMPOSITION OF SOMATIC HYBRID CALLI OF SOLANUM-TUBEROSUM AND NICOTIANA-PLUMBAGINIFOLIA

This paper describes the analysis of chloroplast (cp) DNA and mitochon drial (mt) DNA in 21 somatic hybrid calli of Solanum tuberosum and Nic otiana plumbaginifolia by means of Southern-blot hybridization. Each o f these calli contained only one type of cpDNA; 14 had the N. plumbagi nifolia (Np) type and seven the S. tuberosum (St) type. N. plumbaginif olia cpDNA was present in hybrids previously shown to contain predomin antly N. plumbaginifolia chromosomes whereas hybrids in which S. tuber osum chromosomes predominated possessed cpDNA from potato. We have ana lyzed the mtDNA of these 21 somatic hybrid calli using four restrictio n enzyme/probe combinations. Most fusion products had only, or mostly, mtDNA fragments from the parent that predominated in the nucleus. The hybrids containing mtDNA fragments from only one parent (and new frag ments) also possessed chloroplasts from the same species. The results suggest the existence of a strong nucleo-cytoplasmic incongruity which affects the genome composition of somatic hybrids between distantly r elated species.