Two Nicotiana occidentalis accessions enable gene identification for Type II hybrid lethality by the cross to N. sylvestris

Hybrid lethality, meaning the death of F(1) hybrid seedlings, has been observed in many plant species, including Nicotiana. Previously, we have revealed that hybrids of the selected Nicotiana occidentalis accession and N. tabacum, an allotetraploid with S and T genomes, exhibited lethality characterized by the fading of shoot color. The lethality was suggested to be controlled by alleles of loci on the S and T genomes derived from N. sylvestris and N. tomentosiformis, respectively. Here, we extended the analysis of hybrid lethality using other two accessions of N. occidentalis identified from the five tested accessions. The two accessions were crossed with N. tabacum and its two progenitors, N. sylvestris and N. tomentosiformis. After crosses with N. tabacum, the two N. occidentalis accessions yielded inviable hybrid seedlings whose lethality was characterized by the fading of shoot color, but only the T genome of N. tabacum was responsible for hybrid lethality. Genetic analysis indicated that first-mentioned N. occidentalis accession carries a single gene causing hybrid lethality by allelic interaction with the S genome.