Breeding new varieties

Abstract

The methods employed and the approaches taken in breeding any plant species are largely dictated by the natural reproductive mechanisms that the species possesses and how these are exploited under domestication. In this way plant breeding methods are usually categorized into distinct groups, the most obvious distinction being made between those capable of self-pollination (thus being readily inbred and allowing the derivation of genetically homozygous, true-breeding lines) and those which for a number of reasons have to be cross-pollinated to give seed (thus they are usually marketed as out-bred populations or as hybrids in order to retain genetical heterozygosity). This distinction is, however, often more a theoretical convenience than a practical reality since other factors, usually biological, agronomic or economic, influence the methods used. Another plant breeding and selection system commonly identified is where the plant is readily reproduced by asexual means. In such cases clonal reproduction can be used as a method to exploit the species in terms of production. Again, however, the possibilities within this simple heading are many. For example, species such as grasses are capable of being multiplied extensively by asexual means but are sown by gardeners and farmers alike as seed. Their potential for asxual reproduction is often exploited, however, in the breeding programme itself.