Agronomic performance of Polalta-derived breeding lines resistant to tomato spotted wilt virus
Tomato spotted wilt virus (TSWV) is one of the most important pathogens threatening tobacco cultivation. The dark-cured cultivar Polalta is TSWV-resistant, but it cannot be easily incorporated into breeding programs, because its hybridization with other cultivars leads to morphological deformations in the hybrids. Nevertheless, few doubled haploids (DH) have been derived from hybrids of this cultivar at IUNG. These lines carry a Nicotiana alata introgression that is associated with TSWV resistance and located in the 0–40 cM region on linkage group 7 (LG7).
This study aimed to assess the phenotype and agronomic performance of advanced breeding lines that are F4 populations derived from the DH lines and a flue-cured cultivar. The study plant material was derived from segregation of F2 populations obtained from two DH lines. First, F2 plants were screened with N. alata- and N. tabacum-specific markers designed for three loci located in the 0-40 cM region on LG7 to select plants homozygous for the N. alata introgression (Ala-Ala-Ala), F2 plants without the introgression (Tob-Tob-Tob), and a recombinant with a partial introgression (Ala-Ala-Tob). Then, F4 plants obtained from each of these three F2 categories were subjected to assessment of morphology, deformation degree, and yield.
The phenotypes of the Ala-Ala-Ala and Tob-Tob-Tob F4 populations were comparable, as all or nearly all plants had good or very good phenotype and no symptoms of deformation. The yield of the Ala-Ala-Ala F4 populations was 2290–2522 kg/ha and significantly higher than that of the original DH lines (1686–1719 kg/ha). In contrast, half of the Ala-Ala-Tob F4 plants had a bad morphology; almost all of them showed thickening and irregularity of the leaf veins, and their yield did not differ significantly from that of the DH lines. Such results suggest a detrimental effect of recombination in the genetic environment of a flue-cured cultivar.