The aim of all plant breeding is to “improve” upon nature in some way. Unsatisfied by a dwarf habit or single flowers, for example, the plant breeder tries to alter the gene pool to create a structural difference that will enable the plant to meet the desired criteria more exactly.
This science is not new: the Chinese were practicing it more than one thousand years ago. However, modern advances in the understanding of genetics have enabled plant breeders to become increasingly sophisticated in their work, while the recent controversy over genetically modified (CM) plants has brought the subject into the arena of public debate.
How plants reproduce
To understand the plant breeding process, you need to know how plants reproduce using the process of pollination, in which the male anthers in a flower shed pollen that is transferred via the stigma to the female ovule in a flower. Once the ovule is fertilized, a seed develops and, given the right conditions, this seed will later germinate to produce the next generation of the plant, bearing the characteristics of both its parents. In a garden setting, it is never completely clear which plant’s pollen has fertilized another plant’s ovule, and the offspring can, therefore, be something of a surprise. Plant breeders who wish to control the characteristics of the progeny take great care to ensure the parentage of the new generation of plants, and those who wish to experiment will actually carry out the pollination process themselves.
The seed of a plant is capable of independent life from the moment it is shed, provided the conditions are right, and these vary from plant to plant. Heat, moisture and oxygen all play a part in this development, and many seeds are able to remain viable but dormant for a number of years, until exactly the right conditions act as a catalyst for germination.
While we normally expect plants to carry on reproducing themselves in this way, mankind has, for a whole host of reasons, decided to give nature a helping hand at various points. The aim of the plant breeder is to manipulate the processes of nature, in which cells from the parent plant combine to create various possible genetic combinations, leading to different traits or characteristics. In this way, some hybrid varieties will grow tall, for example, others small. Some traits in plants (just as in people) are recessive and some are dominant, thereby assuring that certain characteristics are more likely to be retained over generations of breeding.
Selective plant breeding attempts to gather attractive traits into a particular category. While this used to be, to some extent, a game of trial and error, new research into DMA is making it increasingly likely that plant breeders can conjure characteristics to order.
There are two principal methods of pollination: wind pollination and insect pollination. Plants have adapted their pollen to suit one or another of these methods. Wind pollination demands copious quantities of pollen grains, all of which must be light and easily blown around. For example, a hazel bush of average size with 300 male catkins would yield over 600 million pollen grains. In wind-pollinated plants, fragrance and nectar are usually absent.
In insect-pollinated plants, various helpful devices have been developed that enable the insect to do the job of pollination more efficiently “Flight-path” markings on the petals indicate the route to the pollen grains, and the pollen grains are heavier and stickier, ensuring that they cling to the insect’s legs. Some other flowers have characteristics that make them particularly attractive to certain insects—a long spur, for example, may mean that the flower attracts only butterflies that have a particularly long proboscis, which reaches down to collect the ncclar.
When buying plants, you will often find that they have been categorized according to the way in which they have been bred. Plants described as open-pollinated have been allowed to breed naturally, with no specialty hybridization. Progeny of these plants will breed more or less true to type.