Recurrent backcrossing is a traditional breeding method that is commonly employed to transfer alleles at one or more loci from a donor to an elite variety. In order to develop male-sterile elite tomato lines, marker-assisted foreground and background selections were performed during backcross breeding. Compared to conventional backcrossing, marker-assisted backcrossing (MABC) is extremely useful for recovery of a recurrent parent's genetic background. For foreground selection, the tomato mutant anthocyanin absent (aa) presents a green hypocotyl during the seedling stage. Lines carrying the Aa genotype were selected from BC1F1 and BC2F1 populations using indel markers derived from the unique aa mutation of T2-517. This trait has been utilized in marker-assisted selection of male sterile 10 (ms10) at the seedling stage because their corresponding loci are closely linked on chromosome 2. For background selection, a total of 48 single nucleotide polymorphism (SNP) markers obtained from resequencing data between the MR10-3211 and T2-517 lines evenly distributed in the tomato genome were finally selected. BC1F1 and BC2F1 plants carrying the heterozygous (Aa) genotype were subjected to background selection using a set of 48 SNP markers. Multiple genotype analysis was done using a high-throughput genotyping system. As a result, one plant, 87.5% similar to the recurrent parent genome in the BC1F1 generation, and three plants with a 95.5% recovery rate of the recurrent parent genome in the BC2F1 generation, were selected. These selected plants were fixed in the BC 2 F 2 and BC 2 F 3 generations for the male sterile tomato elite line. We therefore demonstrate the utility of the MABC method for the recovery of recurrent parent genomes in tomato breeding strategies.

The family Schisandraceae is a basal angiosperm plant group distributed in East and Southeast Asia and includes many medicinal plant species such as Schisandra chinensis. In this study, mitochondrial genomes (mitogenomes) of two species, Schisandra repanda and Kadsura japonica, in the family were characterized through de novo assembly using sequencing data obtained with Oxford Nanopore and Illumina sequencing technologies. The mitogenomes of S. repanda were assembled into one circular contig (571,107 bp) and four linear contigs (10,898–607,430 bp), with a total of 60 genes: 38 protein-coding genes (PCGs), 19 tRNA genes, and 3 rRNA genes. The mitogenomes of K. japonica were assembled into five circular contigs (211,474–973,503 bp) and three linear contigs (8,010–72,712 bp), with a total of 66 genes: 44 PCGs, 19 tRNA genes, and 3 rRNA genes. The mitogenomes of the two species had complex structural features with high repeat numbers and chloroplast-derived sequences, as observed in other plant mitogenomes. Phylogenetic analysis based on PCGs revealed the taxonomical relationships of S. repanda and K. japonica with other species from Schisandraceae. Finally, molecular markers were developed to distinguish between S. repanda, K. japonica, and S. chinensis on the basis of InDel polymorphisms present in the mitogenomes. The mitogenomes of S. repanda and K. japonica will be valuable resources for molecular and taxonomic studies of plant species that belong to the family Schisandraceae.