Mapping of quantitative trait loci conferring resistance to brown spot in flue‐cured tobacco (Nicotiana tabacum L.)

With 2 figures and 1 table ABSTRACT: Brown spot (BS) caused by Alternaria alternata is one of the most destructive foliar diseases affecting tobacco (Nicotiana tabacum L.) production and quality in China. Breeding of BS‐resistant cultivars is difficult because the resistance has proved to be quantitatively inherited. To facilitate marker‐assisted selection, we carried out a study of mapping quantitative trait loci (QTLs) for BS resistance. We developed an F2 population consisting of 213 individuals from a cross between a BS‐susceptible cultivar ‘Changbohuang’ (CBH) and a BS‐resistant cultivar ‘Jinyehuang’ (JYH) and constructed a genetic map consisting of 196 simple sequence repeat (SSR) markers based on this population. Using disease index (DI) as the indicator of BS resistance, we detected three QTLs located between SSR markers TM20534 and TM10737, TM10589 and TM10216, and TM10443 and PT60669, respectively. The resistant alleles of the three QTLs were all from the resistant parent JYH. The three QTLs together could explain ∼86% of the DI difference between the two parents in total, with ∼61% explained by their additive effects. Therefore, the three QTLs will be useful for BS‐resistance breeding.