Plant Breeding

In the view of a breeder, exotic germplasm is all plant material not adapted to the area he is breeding for. Such material may be wild types or other varieties that are, of course, adapted to their (‘exotic’) areas of origin. Despite their lack of adaptation to the new area, exotic material may have important characteristics that could enhance the quality or performance of material into which it is introduced. Examples of characteristics or traits introduced from exotic material are resistances to fungi or viral diseases, and mechanisms useful for breeding hybrids (cytoplasmic male sterility and restorer genes).

Exotic material requires a long period of breeding and large financial investment to be incorporated into improved varieties. This limits its direct use by breeders, who prefer crossing improved and adapted germplasm in breeding programs.

A plant breeder is a person who either breeds or discovers and further develops a variety, and could work in a private enterprise or public organisation or be a farmer. Just the discovery of a variety does not constitute breeding.

Several of the many beneficial activities undertaken by breeders are described in the ISF brochure ‘Seeds for Mankind’ in the chapter Plant Breeders’ Objectives. Among them are higher and stable yields, pest and drought resistant varieties and quality traits. In the last 50 years a 30-60% productivity increase has been realised as a result of genetic improvement made by plant breeders.

ISF considers the definition used in the 1991 Act of the UPOV Convention to be the most appropriate. It reads as follows:

‘Variety’ means a plant grouping within a single botanical taxon of the lowest known rank, which grouping, irrespective of whether the conditions for the grant of a breeder’s right are fully met, can be:

• defined by the expression of the characteristics resulting from a given genotype or combination of genotypes,
• distinguished from any other plant grouping by the expression of at least one of the said characteristics and
• considered as a unit with regard to its suitability for being propagated unchanged

Molecular breeding developed in the 80s with the evolution of DNA marker technologies. The use of molecular markers in association with linkage maps and genomics to select plants with desirable traits based on a genetic assay(s) can make plant breeding more precise, rapid and cost effective in comparison to phenotypic selection. It also offers the possibility of addressing previously unattainable goals.

There are many applications for the use of DNA markers in breeding programs and they can be arranged in the four following broad groups defined by the goal:

• enhanced knowledge of breeding material and systems, e.g. better understanding of Quantitative Trait Loci (QTL) and as a result more effective breeding
• rapid introgression or backcross breeding of simple characters: the number of back-crosses required can be reduced drastically if markers for the character to be introduced and for the genetic background of the recurrent parent are identified
• early or easy indirect character selection: this is important for genes that cannot be detected at an early development stage, e.g. high lysine and tryptophan genes in maize
• new goals not possible through traditional breeding: e.g. pyramiding disease resistance genes with indistinguishable phenotypes

Today, the main DNA markers used in breeding programs are Amplified Fragment Length Polymorphism (AFLP), microsatellites (SSRs) and Expressed Sequence Tags (ESTs). Each of these markers has different advantages and limits. Although still limited in the area of plants, the use of single nucleotide polymorphisms or SNPs (pronounced "snips") is fast developing as a marker for germplasm fingerprinting, marker-assisted backcrossing and breeding. It is likely that general development in DNA marker technology will bring new tools capable of very high throughput genotyping for genetic mapping, marker assisted breeding and plant germplasm protection.

Any genetic material of plant origin that is of potential value for creating improved germplasm is a plant genetic resource. Plant genetic resources for food and agriculture are, in general, sub-divided in the following five categories:

• wild and weed species that are closely related to cultivated species
• landraces
• special genetic stocks including elite and current breeders' lines
• cultivated varieties
• obsolete varieties

The two first categories are often termed ‘exotic germplasm’ by plant breeders, since such materials require long-term pre-breeding programmes in order to gradually transfer their attractive characteristics into an improved and adapted genetic background that can be used in variety breeding.

Today due to genetic engineering, genes from unrelated species are also considered as plant genetic resources. Examples of such genetic resources include Arabidopsis from which genes of interest are being introduced into pea and legumes whose ability to form nodules is a characteristic of interest in tomato.

Not all genetic resources have the same immediate utility. Much depends on the crop and the trait of interest. Wild relatives of cultivated species, for instance, require extensive adaptation and pre-breeding before they can be used in breeding of cultivated varieties. Public or private breeders use mostly germplasm from adapted and productive commercial varieties in the creation of new varieties.