Marker-Assisted Selection in Tomato Breeding
ABSTRACT The cultivated tomato, Solanum lycopersicum L., is the second most consumed vegetable crop after potato and unquestionably the most popular garden crop in the world. There are more varieties of tomato sold worldwide than any other vegetable crop. Most of the commercial cultivars of tomato have been developed through phenotypic selection and traditional breeding. However, with the advent of molecular markers and marker-assisted selection (MAS) technology, tomato genetics and breeding research has entered into a new and exciting era. Molecular markers have been used extensively for genetic mapping as well as identification and characterization of genes and QTLs for many agriculturally important traits in tomato, including disease and insect resistance, abiotic stress tolerance, and flower- and fruit-related characteristics. The technology also has been utilized for marker-assisted breeding for several economically important traits, in particular disease resistance. However, the extent to which MAS has been employed in public and private tomato breeding programs has not been clearly determined. The objectives of this study were to review the publically-available molecular markers for major disease resistance traits in tomato and assess their current and potential use in public and private tomato breeding programs. A review of the literature indicated that although markers have been identified for most disease resistance traits in tomato, not all of them have been verified or are readily applicable in breeding programs. For example, many markers are not validated across tomato genotypes or are not polymorphic within tomato breeding populations, thus greatly reducing their utility in crop improvement programs. However, there seems to be a considerable use of markers, particularly in the private sector, for various purposes, including testing hybrid purity, screening breeding populations for disease resistance, and marker assisted backcross breeding. Here we provide a summary of molecular markers available for major disease resistance traits in tomato and discuss their actual use in tomato breeding programs. It appears that many of the available markers may need to be further refined or examined for trait association and presence of polymorphism in breeding populations. However, with the recent advances in tomato genome and transcriptome sequencing, it is becoming increasingly possible to develop new and more informative PCR-based markers, including single nucleotide polymorphisms (SNPs), to further facilitate the use of markers in tomato breeding. It is also expected that more markers will become available via the emerging technology of genotyping by sequencing (GBS).
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ABSTRACT: When a wild species' allele at a quantitative trait locus (QTL) conferring a desirable trait is introduced into cultivated species, undesirable effects on other traits may occur. These negative phenotypic effects may result from the presence of wild alleles at other closely-linked loci that are transferred along with the desired QTL allele (i.e., linkage drag), and/or from pleiotropic effects of the desired allele. Previously, a QTL for resistance to Phytophthora infestans on chromosome 5 of Solanum habrochaites was mapped and introgressed into cultivated tomato (S. lycopersicum). Near-isogenic lines (NILs) were generated and used for fine-mapping of this resistance QTL, which revealed coincident or linked QTL with undesirable effects on yield, maturity, fruit size, and plant architecture traits. Subsequent higher-resolution mapping with chromosome 5 sub-NILs revealed the presence of multiple P. infestans resistance QTL within this 12.3 cM region. In our present study, these sub-NILs were also evaluated for 17 horticultural traits, including yield, maturity, fruit size and shape, fruit quality, and plant architecture traits in replicated field experiments over two years. Each previously detected single horticultural trait QTL fractionated into two or more QTL. A total of 41 QTL were detected across all traits, with ~30% exhibiting significant QTL × environment interactions. Co-location of QTL for multiple traits suggests either pleiotropy or tightly-linked genes control these traits. The complex genetic architecture of horticultural and P. infestans resistance trait QTL within this S. habrochaites region of chromosome 5 presents challenges and opportunities for breeding efforts in cultivated tomato.G3-Genes Genomes Genetics 10/2013; · 1.79 Impact Factor
- BMC Plant Biology 12/2013; 2013(13):197. · 4.35 Impact Factor
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ABSTRACT: The food production and processing value chain is under pressure from all sides—increasing demand driven by a growing and more affluent population; dwindling resources caused by urbanization, land erosion, pollution and competing agriculture such as biofuels; and increasing constraints on production methods driven by consumers and regulators demanding higher quality, reduced chemical use, and most of all environmentally beneficial practices ‘from farm to fork’. This pressure can only be addressed by developing efficient and sustainable agricultural practices that are harmonized throughout the value chain, so that renewable resources can be exploited without damaging the environment. Bridges must, therefore, be built between the diverse areas within the food production and processing value chain, including bridges between different stages of production, between currently unlinked agronomic practices, and between the different levels and areas of research to achieve joined-up thinking within the industry, so that the wider impact of different technologies, practices and materials on productivity and sustainability is understood at the local, regional, national and global scales. In this article, we consider the challenges at different stages and levels of the value chain and how new technologies and strategies could be used to build bridges and achieve more sustainable food/feed production in the future.Molecular Breeding 12/2013; · 3.25 Impact Factor