The influence of Nicotiana alata-derived introgression on plant malformations of tobacco breeding lines resistant to tomato spotted wilt virus
Tomato spotted wilt virus (TSWV) is one of the most destructive viruses for tobacco cultivation. Cultivar “Polalta” carries a resistance gene introgressed from a wild species, Nicotiana alata, but the use of this cultivar in breeding is hampered by morphological deformations of hybrids resulting from crosses with other cultivars. Over the last decade, a few breeding lines (e.g. DH3 and DH6) were derived at IUNG from cultivar “Polalta” through androgenesis and selection of TSWV-resistant genotypes. The aim of this study was to characterize genomic location and phenotypic effects of the N. alata introgression in these breeding lines. “Polalta”, N. alata, and N. tabacum were subjected to whole genome sequencing, and comparison of the obtained sequences allowed for locating N. alata introgression in cultivar “Polalta” on linkage group 7 in a region between 0-40 cM. Then, N. alata and N. tabacum sequences from this region were used to design species-specific primers in order to detect the presence of this introgression in DH3 and DH6 lines and F2 plants derived from crosses between these two lines and a high-quality flue-cured cultivar “WAC 121D7”. The above-mentioned species-specific primers were used to genotype a segregating F2 population grown in field conditions. Among the 1,543 F2 plants, 15.3 % were homozygotes with introgression (ALA/ALA), 51.3 % were heterozygotes, and 33.2 % were homozygotes without introgression (“tobacco type”, TOB/TOB). Only three recombinant plants (0.3 %) were detected in the F2 studied population. Morphological deformations, such as thick, irregular leaf veins and sometimes also abnormally narrow leaves, were observed in approximately half of the ALA/ALA homozygotes and heterozygotes (in 55.1 % and 47.7 % of plants, respectively). In contrast, only 29.5 % of TOB/TOB homozygotes showed such deformations. Therefore, N. alata introgression is likely to carry a genetic factor that has a negative impact on morphology of the hybrids.