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The total growth duration (TGD), the days from emergence to maturation of the soybean, can be divided into vegetative period (VP) and reproductive period (RP). The ratio of RP to VP (R/V) is an index to investigate evolutionary trends and understand the relationships between different growth periods. To increase our understanding of growth period traits with emphasis on R/V, four generation segregated populations, including P, P, F, F, and F were constructed. Joint segregation analysis revealed that R/V was controlled through major genes plus polygenes. QTL mapping result showed that a total of 22 QTLs were associated with growth period traits. One major effect QTL for R/V, qR/V-1, was mapped on the C2 linkage group, and accounted for 46.90 and 33.72 % of the phenotypic variance under spring and summer sowing season conditions, respectively. The parent bands of the major gene were ubiquitous in the soybean germplasms. The chromosome adjacent interval of qR/V-1 was proved to be associated with VP, TGD, RP, and photo-thermal sensitivity of R/V. However, the QTL showed different effects on different growth period traits. In addition, the 2 minor-effect QTLs for R/V could not be detected repeatedly for others growth period traits. These results indicated that the R/V were controlled through differential pathways with other growth period traits, although one major effect QTL was mapped to the same region. [ABSTRACT FROM AUTHOR]

Brown spot (BS) is a destructive foliar disease in tobacco (Nicotiana tabacum L.) and is caused by Alternaria alternata. BS poses a serious threat to tobacco production worldwide. To develop molecular markers that are tightly linked to BS resistance for marker-assisted selection (MAS), F2, F2:3 and BC3F2:3 populations were developed from a cross between a source of BS resistance Jingyehuang (JYH) and a BS susceptible flue-cured variety NC82. One hundred eighty-one F2 individuals, 180 F2:3 lines and 256 BC3F2:3 lines were evaluated for field resistance under different environments and quantitative trait loci (QTL) were identified by linkage mapping. A major QTL was mapped on chromosome15; this QTL explained 8.6-18.0% of the phenotypic variation under different conditions. Furthermore, 219 accessions were evaluated for their responses to BS at two sites, and association mapping (AM) was used to verify the chromosomal region harboring the major QTL. The AM results showed that six significant marker-trait associations were detected at two sites. Among these markers, the marker Indel53 within the specific chromosomal region exhibited the most significant association with resistance to BS and explained 20.0 and 21.5% of the phenotypic variation at the two sites, respectively. An approximately 2-Mb physical interval at the locus of marker Indel53 contained 31 predicted genes; quantitative real-time PCR results suggested that two of these genes (Nitab 4.5_0000264g0050.1 and Nitab 4.5_0000264g0130.1) were probable candidate genes for resistance to BS. In summary, our results suggested that the novel major QTL from tobacco variety JYH for resistance to BS provided partial effective resistance against A. alternata and was useful for MAS of resistance to BS in tobacco breeding. [ABSTRACT FROM AUTHOR]

Tobacco mosaic virus (TMV) caused serious loss in yield and quality of tobacco every year. It is a long-term goal to improve the tobacco resistance against TMV by tobacco breeding. N gene was the firstly reported TMV-resistant gene, which showed resistance against all Tobamoviruses except the Ob stain and belonged to the toll-interleukin-1 receptor/nucleotide-binding site/leucine-rich repeat class of plant resistance (R) genes. At present, N gene had already been widely used in tobacco conventional breeding, but there is rare available molecular maker used in marker-assisted selection of TMV resistance. In this study, we designed a pair of primers that specific amplify N gene fragment based on the sequence of N gene intron III, named N-marker. Then, we identified TMV resistance by two selecting methods, PCR with N-marker and inoculated with the TMV-C strain. Results from the two method showed that (1) 13 varieties among 67 tobacco varieties displayed hypersensitive reaction when inoculated with the TMV-C strain, also contained N gene fragments screened by PCR with N-marker; (2) 105 strains of 200 BC1 strains showed resistance against TMV when inoculated with TMV-C strain, meanwhile, 103 of the 105 strains contained N gene fragment verified by PCR with N-marker. Therefore, the N-marker is reliable for high throughput screening of germplasm resources and tobacco breeding materials in selection of N-mediated TMV resistance. Our study not only developed a molecular marker for tobacco breeding, but also identified new germplasm resources that are resistant to TMV. [ABSTRACT FROM AUTHOR]