| Tobacco brown spot is one of the most significant fungal diseases in tobacco production. With the increase of acreage in recently years, the damage increasingly heavy, resulting in a important economic loss. The cultivation of resistant variety is the main control measure. Due to lack of resistant cultivars, through the screening of resistant source, the inheritance of resistance to tobacco brown spot disease in two major resistant materials(Jingyehuang and Beinhart1000-1) has been carried out. In this study, the F2、F2:3 and NIL populations were built from a cross between the resistant variety Jingyehuang and the susceptible variety NC82 to be used for fine-mapping the major QTL which tightly linkage to brown spot disease, and to speed up the process of resistance breeding via marker-assisted selection(MAS). The specific conclusions are summarized as follows:1. The resistance genetic analysis of tobacco brown spot diseaseTobacco cultivars Jingyehuang and Beinhart1000-1, have shown effective resistance to brown spot disease. In this study, four generations(P1, P2, F1, F2) were developed as experimental materials from two crosses between the two cultivars and susceptible variety NC82. The joint segregation analysis method of mixed major gene plus polygene genetic model was used to investigate the inheritance of resistance to brown spot disease in tobacco. The results showed that the inheritances of both Jingyehuang and Beinhart1000-1 fitted to a mix genetic model of two major genes with additive-complete dominance effects plus poly-genes with additive-dominance effects(E-5 model). For high resistance material Jingyehuang, the additive effect of the first major gene was larger than the second one. For high resistance material Beinhart1000-1, the additive effect of two major genes was equal. Heritabilities of the major genes was 64.77% in Jingyehuang × NC82, 63.88% in Beinhart1000-1 × NC82 in F2 populations, indicating that resistances to brown spot disease in tobacco cultivars Jingyehuang and Beinhart1000-1 were mainly controlled by major genes.2. The QTL mapping for the resistance of tobacco brown spot diseaseA genetic map constructed by the F2, F2:3 populations of Jingyehuang and NC82 which is 50.2c M, contains 10 markers. Based on these populations, one major effect QTL related the resistance gene of brown spot disease was fine mapped in the interval which is between J9-4a to PT60177. The genetic distance is 3.3c M and we found 53 possible candidate genes in this interval.3. The cultivation of NILs carrying target geneIn the previous study, a resistance-related QTL named q BS23-1 has been mapped using the F2 populations come from Jingyehuang × NC82. Based on flanking markers of the major effect QTL, the foreground and background of BC2F1 populations has been selected by using 121 pairs markers. Utilizing whole genome genotyping to 8 individuals carrying target gene among BC2F1 populations, we found the 9-2-28 plant own the highest genetic background response rate, 93.4%, ultimately. Then let the line continue to backcross with NC82 in order to get a BC3F1 individual which is carrying the target segment and posses a higher genetic background response rate.4. Distribution of major QTL in different tobacco varietiesThe banding patterns of 196 different tobacco cultivars were analyzed by utilized the SSR primers J9-4a and PT60177 which were tightly linked to the major effect QTL of resistance. It turns out that there is a significant difference between the materials carrying dominant loci and the remaining material. The proportions of materials carrying dominant loci and recessive loci linked to the major effect QTL are very high. According to the primer PT60177, the low proportion of dominant loci explained that dominant loci has a high research potential in tobacco brown spot disease resistance breeding. |
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