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Agronomic traits such as plant height (PH), leaf number (LN), leaf length (LL), and leaf width (LW), which are closely related to yield and quality, are important in tobacco (Nicotiana tabacum L.). To identify quantitative trait loci (QTLs) associated with agronomic traits in tobacco, 209 recombinant inbred lines (RILs) and 537 multiparent advanced generation intercross (MAGIC) lines were developed. The biparental RIL and MAGIC lines were genotyped using a 430 K single-nucleotide polymorphism (SNP) chip assay, and their agronomic traits were repeatedly evaluated under different conditions. A total of 43 QTLs associated with agronomic traits were identified through a combination of linkage mapping (LM) and association mapping (AM) methods. Among these 43 QTLs, three major QTLs, namely qPH13-3, qPH17-1 , and qLW20-1 , were repeatedly identified by the use of various genetically diverse populations across different environments. The candidate genes for these major QTLs were subsequently predicted. Validation and utilization of the major QTL qLW20-1 for the improvement of LW in tobacco were investigated. These results could be applied to molecular marker-assisted selection (MAS) for breeding important agronomic traits in tobacco. [ABSTRACT FROM AUTHOR]

Phytophthora nicotianae is highly pathogenic to Solanaceous crops and is a major problem in tobacco production. The tobacco cultivar Beihart1000-1 (BH) is resistant, whereas the Xiaohuangjin 1025 (XHJ) cultivar is susceptible to infection. Here, BH and XHJ were used as models to identify resistant and susceptible genes using RNA sequencing (RNA-seq). Roots were sampled at 0, 6, 12, 24, and 60 h post infection. In total, 23,753 and 25,187 differentially expressed genes (DEGs) were identified in BH and XHJ, respectively. By mapping upregulated DEGs to the KEGG database, changes of the rich factor of "plant pathogen interaction pathway" were corresponded to the infection process. Of all the DEGs in this pathway, 38 were specifically regulated in BH. These genes included 11 disease-resistance proteins, 3 pathogenesis-related proteins, 4 RLP/RLKs, 2 CNGCs, 7 calcium-dependent protein kinases, 4 calcium-binding proteins, 1 mitogen-activated protein kinase kinase, 1 protein EDS1L, 2 WRKY transcription factors, 1 mannosyltransferase, and 1 calmodulin-like protein. By combining the analysis of reported susceptible (S) gene homologs and DEGs in XHJ, 9 S gene homologs were identified, which included 1 calmodulin-binding transcription activator, 1 cyclic nucleotide-gated ion channel, 1 protein trichome birefringence-like protein, 1 plant UBX domain-containing protein, 1 ADP-ribosylation factor GTPase-activating protein, 2 callose synthases, and 2 cellulose synthase A catalytic subunits. qRT-PCR was used to validate the RNA-seq data. The comprehensive transcriptome dataset described here, including candidate resistant and susceptible genes, will provide a valuable resource for breeding tobacco plants resistant to P. nicotianae infections. [ABSTRACT FROM AUTHOR]