Development of codominant markers related to powdery mildew resistance from N. tomentosiformis origin
Powdery mildew is a common tobacco plant fungal disease which can reduce growers' crop yields, particularly in South Africa, Asia and Europe. Three different resistance sources are known, coming from wild tobacco species N. tomentosiformis and N. glutinosa, or from N. tabacum. The latter has recently been identified as a recessive resistance controlled by two closely linked mlo genes.
In this study, N. tomentosiformis dominant resistance was investigated in a F2 flue-cured population segregating for powdery mildew resistance. This resistance was first introgressed into the Zimbabwean variety TB 22, a flue-cured line obtained from a hybrid between N. tabacum and N. tomentosiformis. The resistance was then introduced into modern breeding tobacco lines in Bergerac, France.
RNA-Seq analysis was used to compare resistant and susceptible F2 plants, but also to identify single nucleotide polymorphisms (SNPs) between them. Polymorphic contigs were compared to the reference genome available on Solgenomics, showing that the polymorphism characterising resistant genotypes is spanned on a large portion of chromosome 19. Linkage mapping using SNPs and SSR markers confirmed this finding. SNPs were confirmed on a larger set of tobacco varieties using RNA-seq data mapped to Nt19. From these results, KASP™ markers were designed, enriching the panel of tools available for efficient breeding of powdery mildew resistant lines.