Mapping and validation of the quantitative trait loci for leaf stay‐green‐associated parameters in maize

Functional stay‐green is generally regarded as a desirable trait of varieties in major crops including maize. In this study, we used an F_3:4 recombinant inbred line population with 165 lines from a cross between a stay‐green inbred line (Zheng58) and a model inbred line (B73) using 211 polymorphic simple sequence repeat markers to map quantitative trait loci for three stay‐green‐associated parameters, chlorophyll content, photosystem II photochemical efficiency and stay‐green area, at maturity stage, detected a total of 23 quantitative trait loci (QTL) on nine chromosomes. Single QTL explained 3.7–13.5% of the phenotypic variance. Additionally, we validated some important stay‐green QTL using a heterogeneous inbred family approach and found that the stay‐green‐associated parameters were significantly correlated with the plant yield. This study may contribute to a better insight into the regulatory mechanism behind leaf stay‐green in maize and a novel development of elite maize varieties with delayed leaf senescence through molecular marker‐assisted selection.     

A genome‐wide association study for partial resistance to southern corn rust in tropical maize

Southern corn rust (SCR) is a fungal disease found on corn in several countries worldwide. In Brazil, the disease can result in productivity losses of 65%, especially in areas with a history of the disease. In this study, the genetic architecture and identification of genomic regions associated with SCR resistance was investigated by performing a genome‐wide association study. Genotyping‐by‐sequencing was performed to carry out the association between single nucleotide polymorphism (SNP) markers and phenotypic data from two environments on a panel of 164 maize inbred lines. Eight SNPs were identified as significant for SCR resistance. These SNPs were colocalized with QTL regions, some of which underlie candidate resistance genes with functions that play an important role in the stress response during pathogen recognition. These candidate genes, involved in plant defense pathways, could be associated with partial resistance to SCR and provide a partial comprehensive insight into the genetic architecture of this trait. After validation of the SNPs, they will be useful for marker–assisted selection and for a better understanding of maize resistance to SCR.     

Construction of high‐throughput genotyped chromosome segment substitution lines in rice (Oryza sativa L.) and QTL mapping for heading date

Chromosome segment substitution lines (CSSLs) provide ideal materials for quantitative trait loci (QTLs) mapping and genetic dissection of complex traits. In this study, we developed a set of CSSL population consisting of 175 lines, which were derived between the recipient ‘Guangluai 4’ and the donor ‘Nipponbare’. Based on 260 molecular markers, we firstly constructed a physical map of core 97 lines. Then, these 97 lines were further genotyped based on resequencing data, and a resequencing‐based physical map was constructed. Compared with the molecular marker‐based physical map, the resequencing‐based physical map of 97 lines contained 367 substituted segments with 252 newly discovered segments. The total size of the 367 substituted segments was 1,074 Mb, which was 2.81 times the size of rice genome. Using the 97 CSSLs as materials, we identified nine QTLs for heading date and three of them were firstly reported. All the QTLs had positive additive effects, ranging from 9.50 to 16.50 days. These CSSLs may greatly help forge a new resource for functional genomics studies and molecular breeding in rice.     

A genetic linkage map in southern‐by‐spring oat identifies multiple quantitative trait loci for adaptation and rust resistance

We developed 178 recombinant inbred lines from a southern‐by‐spring oat population designated as “TxH.” These lines were genotyped to generate a high‐quality linkage map that resolved 6,902 markers into 21 linkage groups that matched closely with the latest hexaploid oat consensus map. Three major quantitative trait loci (QTLs) affecting heading date were found in locations that are consistent with known QTLs and candidate genes, and two other QTLs affecting heading date were found in novel locations. Five QTLs affecting plant height were found. Both sets of QTLs are responsible for transgressive segregation observed for these two traits. Four QTLs affecting resistance to crown rust, caused by the pathogen Puccinia coronata f. sp. avenae, were identified. Two of these QTLs are consistent with known clusters of rust resistance genes, while two may represent new locations of novel rust resistance genes. A complete set of SNP sequences suitable for generating markers for molecular selection is provided.