Marker-assisted breeding (MAB), also known as molecular breeding, refers to a modern breeding process where selection of targeted traits is based on specific molecular markers, such as simple sequence repeats (SSRs) and single nucleotide polymorphism (SNPs). In combination with genetic linkage mapping, plants with desired traits can be easily identified and selected. As a leading plant biotechnology company, Lifeasible has developed fully-fledged MAB platforms to help scientists and plant breeders develop plant breeds with high productivity, great nutritional value, as well as strong resistance against biotic and abiotic stress.

Generally, the MAB process includes three steps: (1) detection and development of DNA markers that are closely linked to desired traits; (2) mapping of the target genes or quantitative trait loci (QTLs) with the help of DNA markers; and (3) selection of traits based on DNA markers. Despite of fairly uniform processes, the specific method may vary depending on the complexity of the trait and the background of target gene(s) or quantitative trait loci (QTLs). Commonly used schemes for MAS are:

• Marker-assisted backcrossing (MABC): MABC is the simplest form of MAS and has been widely used in many species (e.g., rice, wheat, maize, barley, pear, millet, soybean, tomato, etc) for the selection of disease/pest/drought resistant plants. It aims to transfer one or a few genes/QTLs of interest from an inferior genetic source (the donor parent) into a superior cultivar or elite breeding line (the recurrent parent) to improve the desired trait.
• Gene pyramiding: This is a technique to transfer multiple genes/QTLs that associate with single or multiple traits into a cultivar which is deficient of these traits.
• Marker-assisted recurrent selection (MARS): MARS is a scheme which allows performing genotypic selection and intercrossing in the same crop season for one cycle of selection, which provides higher selection efficiency and faster selection process, accelerating the integration of favorable genes from diverse parents into a single genotype.
• Genomic selection (GS): GS is a strategy to select desirable individuals using all the available molecular marker information covering the whole genome based on genomic estimated breeding value (GEBV).

Compared with conventional breeding methods, MAB allows selection of traits as early as the seedling stage and selection of recessive alleles of desired traits in the heterozygous status, resulting in a significantly shortened breeding process. Most importantly, as molecular markers are not affected by environmental factors, targeted traits can be selected regardless of cultivation conditions (place and climate). At Lifesiable, our teams of experienced geneticists, mathematicians, optimization specialists, statisticians, computer scientists, software engineers, and crop breeders have developed a state-of-the-art plant breeding platform to provide tailored protocols for marker discovery and development, population development, genetic map construction, MAS strategy, and other critical aspects of your breeding program. We provide reliable customized services to help you accomplish your research goals.

Figure 1. The general steps of marker-assisted selection (Nadeem et al., 2018).