Читать книгу Principles of Plant Genetics and Breeding - George Acquaah - Страница 152

As will be discussed later in the book, there are several distinct types of cultivars that plant breeders develop – pure lines, hybrids, synthetics, multilines, composites, etc. The type of cultivar is closely related to the breeding system of the species (self‐ or cross‐pollinated), but more importantly on the genetic control of the traits targeted for manipulation. As breeders have more understanding of and control over plant reproduction, the traditional grouping between types of cultivars to breed and the methods used along the lines of the breeding system have diminished. The fact is that the breeding system can be artificially altered (i.e. self‐pollinated species can be forced to outbreed, and vice versa). However, the genetic control of the trait of interest cannot be changed. The action and interaction of polygenes are difficult to alter. As Kearsey notes, breeders should make decisions on the type of cultivar to breed based on the genetic architecture of the trait, especially the nature and extent of dominance and gene interaction (see Section 4.2.5 on gene action), more so than the breeding system of the species.

Generally, where additive variance and additive × additive interaction predominate, pure lines and inbred cultivars are appropriate to develop. However, where dominance variance and dominance × dominance interaction suggest overdominance predominates, hybrids would be successful cultivars. Open pollinated cultivars are suitable where a mixture of the above genetic architecture occurs.