Salinity is a common and increasing problem in many coastal rice producing areas around the world. Salinity tolerance at the reproductive stage in rice is crucial as it determines grain yield. An F2 mapping population was developed from two modern rice cultivars contrasting in tolerance: NSIC Rc222 (a high-yielding salt-sensitive variety released in the Philippines) and BRRI dhan 47 (a salt-tolerant variety released in Bangaldesh). The performance of the F2 population showed transgressive segregation in the yield components under salinity stress of EC 10 dS/m under salinized field conditions. Ninety-six single nucleotide polymorphism (SNP) markers using 96-plex FluidigmTM genotyping were used to construct a linkage map of 1306.2 cM (Kosambi), with an average interval size of 13.6 cM. Seven putative quantitative trait loci (QTLs) for reproductive stage salinity tolerance traits having LOD values ranging from 2.9 to 4.1 were identified on chromosomes 1, 2, 5 and 11, explaining 13.4 to 18.4% of the phenotypic variation. Results of this mapping study identified a genomic region on chromosome 2 that confers salinity tolerance at the reproductive stage as measured by the number of filled spikelets, percent filled spikelets and yield. This study reports the molecular mapping of QTLs controlling reproductive-stage salinity tolerance-related traits, which will be useful in marker-assisted selection and breeding population development in rice.
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Recent advances in next-generation sequencing (NGS) and single nucleotide polymorphism (SNP) genotyping promise to greatly accelerate crop improvement if properly deployed. High-throughput SNP genotyping offers a number of advantages over previous marker systems, including an abundance of markers, rapid processing of large populations, a variety of genotyping systems to meet different needs, and straightforward allele calling and database storage due to the bi-allelic nature of SNP markers. NGS technologies have enabled rapid whole genome sequencing, providing extensive SNP discovery pools to select informative markers for different sets of germplasm. Highly multiplexed fixed array platforms have enabled powerful approaches such as genome-wide association studies. On the other hand, routine deployment of trait-specific SNP markers requires flexible, low-cost systems for genotyping smaller numbers of SNPs across large breeding populations, using platforms such as Fluidigm’s Dynamic Arrays™, Douglas Scientific’s Array Tape™, and LGC’s automated systems for running KASP™ markers. At the same time, genotyping by sequencing (GBS) is rapidly becoming popular for low-cost high-density genome-wide scans through multiplexed sequencing. This review will discuss the range of options available to modern breeders for integrating SNP markers into their programs, whether by outsourcing to service providers or setting up in-house genotyping facilities, and will provide an example of SNP deployment for rice research and breeding as demonstrated by the Genotyping Services Lab at the International Rice Research Institute.
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