FRUIT BREEDING IN THE 21ST CENTURY
The majority of fruit crops have been under cultivation since Neolithic times and have become transformed by continuous selection so that they are far removed from their wild progenitors. At present, the world fruit industry is based on relatively few genotypes that represent unique combinations of attributes and in many instances there is great reluctance to change cultivars. The export banana industry in Latin America is now based on a single clone and the global kiwifruit industry, a newcomer, is based on a single pistillate clone ‘Hayward’. Only a few fruits, such as strawberry and peach, are characterized by a steady replenishment of new and improved cultivars. Genetic improvement of fruit crops has in most cases been achieved by grower selection from natural seedling populations and many cultivars are very old, many dating to the 19th century and earlier. Intense selection and testing combined with fixation of unique genotypes by clonal propagation have resulted in a narrow germplasm base for many fruit crops. The deficiencies inherent in these genotypes in many cases have been amcliorated through cultural practices to prop them up, including rootstocks, insect and disease control practices via chemical pesticides, growth regulators, and special handling and storage technology. Conventional breeding refers to systems for selecting superior genotypes from genetically variable populations derived from sexual recombination. The system is powerful because it is evolutionary and progress can be cumulative with improved individuals continually serving as parents for subsequent cycles of breeding. However, many fruit crops are large plants with long juvenile periods and are often characterized by a combination of high heterozygosity, polyploidy, sterility, and incompatibility. Restraints to progress for conventional breeding include (1) the inability of the sexual system to incorporate variation from non-related species or to incorporate small changes without recombination; (2) the reliance on naturally occurring variation; (3) the linkage of desirable and non-desirable traits; (4) the limitation of selection in detecting infrequent or rare recombinants; (5) the dependence upon time to generate cycles of recombination, space to grow the necessary populations to recover superior recombinants, and resources to be able to select, identify, and evaluate desirable combinations. The biotechnological revolution based upon novel strategies derived from microbial and molecular genetic techniques, includes cell selection, embryo rescue, protoplast fusion, and finally recombinant DNA (transgene) technology, the most powerful and revolutionary technique of the new genetics. Transgenic techniques make it possible to overcome the limitation to the sexual system by permitting the introduction of foreign genes hitherto unavailable to plant breeders and make it possible for the first time to introduce small discrete defined changes into established genotypes. A combination of conventional and unconventional techniques has the potential to greatly improve the fruit industry in the next century.
Janick, J. (1998). FRUIT BREEDING IN THE 21ST CENTURY. Acta Hortic. 490, 39-48