Wild peas vary in their cross-compatibility with cultivated pea (Pisum sativum subsp sativum L.) depending on alleles of a nuclear-cytoplasmic incompatibility locus

Key message Divergent wild and endemic peas differ in hybrid sterility in reciprocal crosses with cultivated pea depending on alleles of a nuclear 'speciation gene' involved in nuclear-cytoplasmic compatibility. Background In hybrids between cultivated and wild peas, nuclear-cytoplasmic conflict frequently occurs. One of the nuclear genes involved, Scs1, was earlier mapped on Linkage Group III. Results In reciprocal crosses of seven divergent pea accessions with cultivated P. sativum, some alleles of Scs1 manifested incompatibility with an alien cytoplasm as a decrease in pollen fertility to about 50 % in the heterozygotes and lack of some genotypic classes among F2 segregants. Earlier, we defined monophyletic evolutionary lineages A, B, C and D of pea according to allelic state of three markers, from nuclear, plastid and mitochondrial genomes. All tested representatives of wild peas from the lineages A and C exhibited incompatibility due to Scs1 deleterious effects in crosses with testerlines of P. sativum subsp. sativum (the common cultivated pea) at least in one direction. A wild pea from the lineage B and a cultivated pea from the lineage D were compatible with the testerline in both directions. The tested accession of cultivated P. abyssinicum ( lineage A) was partially compatible in both directions. The Scs1 alleles of some pea accessions even originating from the same geographic area were remarkably different in their compatibility with cultivated Pisum sativum cytoplasm. Conclusion Variability of a gene involved in reproductive isolation is of important evolutionary role and nominate Scs1 as a speciation gene.