Читать книгу Principles of Plant Genetics and Breeding - George Acquaah - Страница 318

For breeding purposes, vegetatively propagated crops may be grouped into four types based on flowering behavior as follows:

1 3 Those with normal flowers and seed setSpecies in this category produce normal flowers and are capable of sexual reproduction (to varying extents) without artificial intervention (e.g. sugar cane). However, in crop production, the preference is to propagate them sexually. Such species enjoy the advantages of both sexual and asexual reproduction. Hybridization is used to generate recombinants (through meiosis) and introduce new genes into the adapted cultivar, while vegetative propagation is used to indefinitely maintain the advantages of the heterozygosity arising from hybridization.

2 4 Those with normal flowers but poor seed setSome plant species produce normal‐looking flowers that have poor seed set, or set seed only under certain conditions but not under others. These restrictions on reproduction make it unattractive to use seed as a means of propagation. However, the opportunity for hybridization may be exploited to transfer genes into adapted cultivars.

3 5 Produce seed by apomixisThe phenomenon of apomixis results in the production of seed without fertilization, as was first discussed in Chapter 6. Over 100 species of perennial grasses have this reproductive mechanism.

4 6 Non‐flowering speciesThese species may be described as “obligate asexually propagated species” because they have no other choice. Without flowers (or with sterile flowers) those species can only be improved by asexual means. Genetic diversity is not obtained via recombination but by other sources (e.g. mutation).