Plant Sex

To begin to understand plant breeding you need to know a little bit about plant sexual reproduction. In order to breed plants you first need to know the different parts of the flower, because flowers are the sexual organs for plants. (Makes giving flowers romantically an innuendo). In my last blog, (Feb – 17, 2009) I mentioned the benefits and downside to asexual reproduction a.k.a. cloning (see my cloning article)
If you are interesting in improving your plants by breeding, you need to understand sexual reproduction, which means joining male and female sex cells to form a seed.

Parts of the flower--First, you need to know the boy parts vs. the girl parts. Take a look at the pictures I have inserted into this post. Notice the (slightly blurry) white four pointed star shaped structure in the middle, it is called the stigma*; this is the part of the female flower where pollen must first enter. The 8 yellow structures that surround the stigma* are the male parts. The top yellow part is each called an anther*, and the yellow flecks you see are pollen grains being produced (like sperm, it carries the male DNA). For pollination* to occur, pollen must reach the stigma. For fertilization* to occur (seed formation) the pollen must get to the ovary* which is connected to the stigma by a stalk called a style*. At the base of the stigma is the bulging ovary which produces ovules (inside) with have the female DNA (eggs). Another plant in bloom I have growing is pictured on the side bar above the glossary is a Clymentas; Can you see a “hair like structure” sticking out of the middle? If so, maybe you can see several yellowish anthers* above it and surrounding it? That “hair” is the female part (stigma) where pollen must land for pollination and eventually fertilization.
Obviously, flower parts vary greatly in size, shape, color, and number. A general way to tell male parts from female is that the male parts produce a yellow powder (pollen) and the female part usually has a bulge (the ovary) at its base with a long structure (stigma) sticking out. If you are observant it should not take you long to learn the male and female parts of your plant!
Types of flowers -- There could be countless posts about the different types of flowers that exist on all plant species. I have read several papers that break down flowers into three general groups: perfect, imperfect and composite.
Most plants have both male and female sexual organs, if the male and female parts are in the same flower it is a perfect flower* (like the picture in this post). Imperfect flowers* have different combinations of male and female parts, separated in space and time on a plant (separate male and female flowers). Some imperfect plants like jack in the pulpit even change sex from one year to the next. Composite flowers* are actually a cluster of small flowers, called florets, joined together in what is called a flower head (picture a sunflower in your minds eye). The florets can be made up of male or female flower parts.
Composite flowers can be either perfect or imperfect. Perfect flowers can reproduce (make a seed) entirely within one flower, imperfect flowers need two separate flowers in order to pollinate, fertilize and make seeds. Each can be a benefit if you are a good grower. With imperfect flowers you avoid accidental breading which can doom a breeding program to mediocrity. If you are growing a plant that has perfect flowers (that self pollinates) the benefit to breeding is that you simply have to remove the male parts of the flower from one plant, and then take the pollen from another plant to pollinate. You then know the traits of both parent plants (male and female). If you grow a plant that has two different plants male and female (dioecious) or one that does not self pollinate, you will have a more difficult time with being able to have pure breeding* traits for male or female plants.

Common examples of the three flower types
Perfect -- Some common perfect flowers are tomatoes, morning-glories, tulips, snapdragons, petunias, lilies, roses, cherries, apples and many more.
Imperfect -- Examples of plants with separate male and flowers on the same plant are squashes, corn, clematis, bittersweet, and begonias. Plants with male and female flowers on different plants include; hops, asparagus, spinach, holly and mulberry to name a few.
Composite -- Typical composite flowers are zinnias, sunflowers, dandelions, chrysanthemums, asters, marigolds and thousands more. The plant pictured in the upper right coner titled HPS Flower Power is an example of a composite flower.

Sexual reproduction -- Ultimately, plant sex like all sexual reproduction involves combining male and female sex cells. This recombining (shuffling) of traits from two cells creates/provides diversity for natural selection to work on. This process has created the vast diversity of life that now exists on Earth. It is also the pool where plant breeders get their raw materials. One of my committee members while earning my Ph.D. was a blueberry breeder. He would spend time in the Rockies and Andes mountains looking for new and interesting traits in “wild blueberries” and then breed the best wild traits into an already superior commercial line. I am assuming that most of you are just trying to improve or increase the plants you have and don’t want to go into the wild to look for new varieties. Although the diversity created by sexual reproduction is good for the world as a whole; the recombination of traits (genes) during sexual reproduction is a problem for the breeder who wants to know exactly what the offspring will be. This is one reason that plant breeding is not so straight forward. In the next posts, I will talk about how to collect pollen, pollinate female flowers and then I will talk more about heredity and finally I will describe some specific breeding programs and discuss the pros and cons of each.

Good Growing!
Dr. E. R. Myers

1 comment:

hillbilly said...

i have heard of (but never seen) products supposedly able to "convert" female flower parts into male flower parts, effective ONLY on the area of the plant which gets sprayed. from what i've heard, this can be VERY advantageous when attempting to capture plant traits and breeding. if these products exist, do you happen to know where they are available? are the products safe to use on edible as well as ornamental flowers?