Association mapping for resistance to powdery mildew in oriental tobacco (Nicotiana tabaccum L.) germplasm

Powdery mildew caused by Erysiphe cichoracearum is an important fungal disease which threatens tobacco (Nicotiana tabacum L.) production. The objective of this study was to determine DNA markers linked to genomic regions associated with resistance to powdery mildew in tobacco through the association mapping approach. Seventy tobacco genotypes were fingerprinted using 26 simple sequence repeat (SSR) primer pairs which were distributed in several chromosomes of tobacco.A total number of 66 alleles were detected by 26 SSR primers with an average of 2.53 alleles per locus. Based on population structure analysis, the studied genotypes were classified into three groups including Chopogh, PD and Tikolak genotypes. Ou of 325 marker pairs, 6.15% showed a significant level of linkage disequilibrium (LD) (P<0.01). The mean of D´ for all marker pairs was 0.268. Using susceptibility data of the 70 genotypes against fungal agent, three loci (pt30034, pt30008 and pt30159) from linkage groups 22, 11 and 14b of tobacco reference linkage map were identified to be associated with the gene(s) controlling resistance to powdery mildew. The identified markers could be good candidates for marker assisted selection in powdery mildew disease resistance breeding programs. However, like any other quantitative trait, there is a requirement to assess the quality of the obtained quantitative trait loci (QTLs) before marker assisted selection (MAS) become a viable proposition.