The Gene Pool System of Classification
Gene pool of a crop included all cultivars (Obsolete and current) , wild species and wild relatives containing all the genes available for breeding use. Based on degree of relationship, the gene pool of a crop can be divided into three groups, viz. 1) Primary gene pool, 2) Secondary gene pool, 3) Tertiary gene pool (Harland and Dewet, 1971). These are briefly discussed below:
1. Primary Gene Pool (GP1):
The gene pool in which intermating is easy and leads to production of fertile hybrids is known as primary gene pool. It includes plants of the same species or of closely related species which produce completely fertile offspring’s on intermating. In such gene pool, genes can be exchanged between lines simply by making normal crosses. This is also known as gene pool one (GP1). This is the material of prime breeding importance.
2. Secondary Gene Pool (GP2):
The genetic material that leads to partially fertility on crossing with GP1 is referred to as secondary gene pool. It includes plants that belong to related species. Such material can be crossed with primary gene pool, but usually the hybrids are sterile and some of the progeny to some extent are fertile. Transfer of gene from such material to primary gene pool is possible but different. This type of gene pool is also known as gene pool two (GP2).
3. Tertiary Gene Pool (GP3):
The genetic material which leads to production of sterile hybrids on crossing will primary gene pool is termed as tertiary gene pool or gene pool three (GP3). It includes material which can be crossed with GP1, but the hybrids are sterile. Transfer of gene from such material to primary gene pool is possible with the help of special techniques.