Читать книгу Principles of Plant Genetics and Breeding - George Acquaah - Страница 321

There are certain characteristics of clonal propagation that have breeding implications.

 Clonal species with viable seed and high pollen fertility can be improved by crosses.

 Unlike crossing in sexually reproducing species, which often requires additional steps to fix the genetic variability in a genotype for release as a cultivar (except for hybrid cultivars), clonal cultivars can be released immediately following a cross, provided a desirable genotype combination has been achieved.

 When improving species whose economic parts are vegetative products, it is not important for the product of the crossing to be fertile.

 Because of the capacity to multiply from vegetative material (either through methods such as cuttings or micropropagation), the breeder only needs to obtain a single desirable plant to be used as stock.

 Heterosis (hybrid vigor), if it occurs, is fixed in the hybrid product. That is, unlike hybrid cultivars in seed‐producing species, there is no need to reconstitute the hybrid. Once bred, heterozygosity is maintained indefinitely.

 It is more difficult to obtain large quantities of planting material from clones in the short term.

 Plant species that are vegetatively parthenocarpic (e.g. banana) cannot be improved by the method of crossing parents.

 Species such as mango and citrus produce polyembryonic seeds. This reproductive irregularity complicates breeding because clones of the parent are mixed with hybrid progeny.

 Many clonal species are perennial outcrossers and intolerant of inbreeding. These are highly heterozygous.

 Unlike sexual crop breeding in which the genotype of the cultivar is determined at the end of the breeding process (because it changes with inbreeding), the genotype of a clone is fixed and determined at the outset.

 Both general combining ability (GCA) and specific combining ability (SCA), that is performance in crosses, can be fully exploited with appropriate breeding approaches.