Molecular Mapping and Marker‐Assisted Selection of Quantitative Trait Loci in Plants

Abstract

Since the dawn of agriculture, mankind has tried to mould crop plants into more useful types. Over the years, experience and intuition led to the development of sophisticated and successful artificial selection (breeding) of many types of plants for human food, fibre, shelter, profit and pleasure. Just compare the cultivated tomato with some of its small‐ and green‐fruited relatives, or cultivated maize to teosinte. Most of this ‘improvement’ was probably through simple field selection and propagation of desirable genotypes. Scientifically based plant breeding, not appearing until the 20th century, has also had great successes in plant improvement, particularly in disease resistance and yield. Breeders have achieved good results for both single‐gene traits and polygenic traits, but the polygenic traits, encoded by multiple genes often referred to as quantitative trait loci (QTL), are much more difficult to work with. Advances in molecular genetics in the last 20 years have enabled the placement of molecular markers on to maps of the chromosomes of most major crop plants and the subsequent tagging of genes of interest by their placement near these markers. A major goal of these efforts is marker‐assisted selection (MAS), the use of molecular markers to track traits in breeding programmes. In this chapter, we will discuss the basics of molecular mapping in crop plants, the identification of the location of QTL and MAS. While not intended as an exhaustive review of the techniques nor of successes in this field, this chapter will provide lists of crops with linkage maps and QTLs identified to serve as entry points into the literature for investigators interested in pursuing this technology in a particular crop.

Molecular biology of aromatic plants and spices. A review.

“…[4,6] There is often diff erential expression of isozymes in diff erent tissues. As a result, several samplings of the population may be necessary to score all the available isozymes.…”

“…RFLP linkage maps have been constructed for many economically important crops, such as potato, maize, rice, lettuce, sunfl ower, sugar beet, barley and soybean, to give just a few examples (for references, see ref. 4), but concerning aromatic plants and spices the literature is scarce or even lacking with regard to RFLPs.…”

“…All these techniques have enabled the placement of molecular markers on to the maps of chromosomes of most major crop species and the subsequent tagging of genes of interest by their placement near those markers. [4] These important developments in crop species have been followed by some research in aromatic plants.…”