tion of positively acting polygenes of one specific genetic background
is difficult if not impossible because of recombinational dispersion of
genes in each sexual generation. Biotechnology and molecular biology
have provided exciting new tools to the plant breeder, which may help
to circumvent some of the obstacles in the breeding of complex traits.
BIOTECHNOLOGY AND PLANT BREEDING
Plant breeding has been impacted during the last two decades by a
number of technological developments that may enrich plant breeders’
repertoire to achieve breeding progress more quickly or conveniently or
even allow them to design plant traits that were impossible to create by
classical breeding methods. Besides classical breeding methods, biotech-
nological breakthroughs like in vitrofusion and regeneration of plant
cells, and marker-assisted selection (MAS) of monogenic traits as well
as the tracing of quantitative trait loci (QTL) by use of molecular ge-
nomic markers have gained increased importance for plant breeding
(Table 2.1). In tomato, e.g., QTL for quality traits such as soluble solids
content, fruit mass, fruit pH, and fruit shape have been mapped
(Grandillo et al., 1996). In potato, traits such as chip color, tuberization
and tuber dormancy may be traced by molecular markers. For these char-
acters, between 5 and 13 QTL have been identified. In some cases rel-
22 QUALITY AND BREEDING—CULTIVARS, GENETIC ENGINEERING
Classical Breeding- Selection of phenotypes
- Intercrossing, selfing, vegetative cloning of favorable phenotypes
- Inbred line or population or clonal varieties
Marker-Assisted Selection- Mapping of quantitative trait loci (QTL) (e.g., solids content and pH of
tomato pulp, chips quality of potato, -glucan content of barley) - Selection of genotypes instead of phenotypes
Genetic Engineering- Gene suppression by antisense or cosuppression
- Expression of foreign genes (constitutive or tissue-specific)
- Overexpression of native genes
Table 2.1. Approaches in Plant Breeding