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 geno-types were fingerprinted using ۲۶ simple se-quence repeat (SSR) primer pairs which were distributed in several chromosomes of tobac-co. A total number of ۶۶ alleles were detected by ۲۶ SSR primers with an average of ۲.۵۳ alleles per locus. Based on population struc-ture analysis, the studied genotypes were classified into three groups including Chopogh, PD and Tikolak genotypes. Ou of ۳۲۵ marker pairs, ۶.۱۵% showed a significant level of linkage disequilibrium (LD) (P<۰.۰۱). The mean of D´ for all marker pairs was ۰.۲۶۸. Using susceptibility data of the ۷۰ genotypes against fungal agent, three loci (pt۳۰۰۳۴, pt۳۰۰۰۸ and pt۳۰۱۵۹) from linkage groups ۲۲, ۱۱ and ۱۴b of tobacco reference linkage map were identified to be associated with the gene(s) controlling resistance to powdery mil-dew. 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 as-sess the quality of the obtained quantitative trait loci (QTLs) before marker assisted selec-tion (MAS) become a viable proposition.

Keywords:

Linkage disequilibrium , mixed linear model , Nicotiana tabacum , powdery mildew , simple sequence repeat