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


Plant Breeding Introduction

In the next few posts, I hope to begin to explain the art and science of plant breeding. Breeding plants creates new varieties or improves on old varieties. As a hobby anyone can try plant breeding. The crossing techniques (mixing male and female) is easy for many plants and you will get improvements in a couple generations if you choose traits that you see, flower color, plant size, etc. The home hobbyist does not have all the resources of modern plant breeders, but you can still work to improve your plants for your indoor grow area, and/or for your personal preferences.
Plant breeding has been done for 1000’s of years, so it is not rocket science. However, there are a lot of misinformed people when it comes to breeding plants. I have seen so many people buy a seed packet, grow them and get seeds from the plants and tell me their seeds are the same as the original one’s they bought, maybe even call them by the same brand name. Ya, right! Plant breeders spend years and lots of time to get pure breeding* plants. If you mate two hybrids* even though both plants look the same, (say short in height) they will have A LOT of different types of offspring (children), tall, medium and yes some short too, but all the seeds you made will NOT be the same. I hope the following posts will help if you are breeding your plants, and make you think about breeding if you are not. As always, you can send questions/comments to askthedoctor@htgsupply.com.

The art of plant breeding comes in knowing your crop, being curious and making observations.
To define plant breeding, it is the development of a plant cultivar that fits a specific environment and meets the needs of the grower. Plant breeding is applied evolution and applied genetics to effect some permanent genetic change.

One of my teachers in a plant breeding class had a saying,” Don’t get mired in mediocrity”. What this means is that if you are going to attempt to improve plants by breeding, you must be ruthless in which plants you choose to breed. Only the best of the very best can be chosen to start the next generation. Experienced plant breeders know it is not always simple to combine desired traits from one generation to the next; therefore, you can never risk introducing inferior traits in your breeding program. If you breed average plants, you will only get average plants as offspring. You need to pick and choose the best of the best plants to breed to have the greatest chance of getting improved plants. Each time you breed two plants is like dealing a hand of cards. You greatly increase you chance of having a wining hand if you only deal yourself face cards.
Of course, if you have a superior plant, you should consider cloning (see my article at http://htgsupply.com/images/articles/HTGSupply-Cuttings-November-2008.pdf). This is asexual reproduction where there is no mixing of male and female reproductive cells. Many commercial nurseries use a mother plant(s) to provide hundred’s of new cloned plants all that meet their growing needs, each plant exactly the same. The home grower can do the same. However, studies have shown that most plants tend to loose vigor and vitality after being cloned for many years. That is one reason why you always see new cultivars or varieties every few years. After many generations of cloning, plants just don’t pack the same potency or yield. The reasoning seems to be that individual cells of an organism keep track of time with their DNA. What this means is that although the cutting/cloned plant is starting small and getting big, like a juvenile becoming an adult, its cells are the age of the original plant. Older plants as a rule will have less vigor and lower yields.
You may remember the first cloned mammal “Dolly” the sheep… Did you know after ½ the normal life of a sheep she was euthanized (at age 6) due to a lung ailment common in older sheep. Sheep normally live to be 11-12. The 6 year old clone Dolly had arthritis and the body of a sheep suffering from old age. The moral is that eventually, even with cloning, you will need to mix DNA from male and female parts of a plant to reset the genetic clock. When plants under go sexual reproduction the DNA genetic clock is reset at zero, then you can restart cloning for a couple years once a superior plant is found again.

Read my post on How to Select the Right Plants to Breed, if you are serious about plant breeding.
Read my post on Breeding Techniques to see which one is right for you.

Good Growing!


Seed Storage

I will begin talking about breeding plants for the next several weeks. An important thing in plant breeding is seed storage. If you can create a good generation of seeds, you can grow some and create clone generations of their offspring for years. If you can store the unused seed, you can then keep pulling from your seed population for years to clone, and/or a chance to find better traits. Seeds like all things have a limited shelf life. Eventually, no matter what you do, over time seeds will not be able to grow into a healthy plant. I should also mention that storing seeds will also allow you to backcross traits over multiple generations to create the best strain possible with the seeds you have.
Scientists break down seeds into two groups, those that are long lived seeds (store well) and those that are short lived. Many tree species are short lived. These seeds tend to be covered in fleshy fruit, and germinate in the fruit. Conversely, long lived seeds tend to be from plants that are annuals and live in open fields. These seeds tend to have a hard outer covering.
No matter what type of seed your plant produces, seed deterioration is inevitable. You can not stop it, but you can prolong it. There are a few simple rules that will help you improve seed storage. Temperature and relative humidity are the two most important things to keep in mind when storing seeds. But other factors like pathogenic organisms, the seeds maturity when harvested and genetics are important too.

Your first concern seeds can be attacked by various organisms. Fungus is usually the biggest problem. You should be able to keep insects out of your seeds if they are kept in containers. Yet another benefit for indoor growers, you should not have to worry about insects getting at your seeds as they mature on the plant. If you do collect seeds from outside or areas exposed to the outside world you may want to check for small holes in the seeds before storage. Concerning fungus, there are two basic types of fungus that can harm your seeds. The first type is those that affect seeds as they mature on the plant. To fight these fungi, keep the moisture below 65% while the seeds are developing. The other kind of fungus is storage fungus. There are at least two genus of fungi that feed on seeds. They can survive humidity as low as 30%, and temperatures above 0C. (A good reason to keep the humidity and temperature low.) A fungus grows from microscopic spores in the air so it is pretty hard to control. Do not microwave seeds to sterilize them, you will kill the seeds.

The second concern is that all seeds will deteriorate internally over time. So, why do seed deteriorate any way? Seeds are made up of organic molecules, proteins, carbohydrates etc. like all living things, so, free radicals damage cells over time, DNA deteriorates over time, proteins deteriorate, plant structures inside the seed deteriorate , lipids deteriorate etc… Organic molecules need energy to keep their structure. Seeds have a limited energy supply for the cells inside, and when it is gone, deterioration follows.

How do you know if your seeds are deteriorating? Good growers will notice that when your seeds are new (young), the germination period* is shorter. In other words, older seeds tend to take longer to germinate and eventually old seeds will never germinate. Once you notice the germination time lengthening, the writing is on the wall, you have a limited time to grow the remaining seeds. If you are not observant, you may not notice the length of germination, but most people notice when less seeds as a percentage germinate. Young seeds (less than one year) may have a 100% germination rate (every seed germinates). You may notice low seed germination even with young seeds if you have a bad cross*. Even the most healthy seeds age, eventually you will notice less and less of your seeds will germinate over time. One day, you will try to germinate seeds and not one will germinate.
The next observation you can make concerning seed health is that older seeds germinate but the seedlings tend to grow less vigorously. Young seeds often produce fast growing seedlings. You may also notice that more and more seedlings not only grow slower, they grow “funny” with deformed leaves or cotyledons*. Look at (http://www.htgsupply.com/images/articles/HTGSupply-Starting-Article-April-2008.pdf) for more seed dormancy information. If you have been saving seeds for years, you may need to think about creating or buying some new, younger seeds. Breeding is the only way to get “new” plants.
More Symptoms of deterioration You may also notice decreased resistance to environmental stress, and decreased yields when growing plants from older seeds. Decreased yields in some plants begin to occur even before you notice a decrease in the germination rate. If you are growing plants from seeds a few years old, you may have the need to breed. Keep in mind the loss of yield may also occur in cloned plants over time.

Ways to improves seed storage. First, keep your seeds cold. {I have some useful information under my HERB STORAGE WRAP-UP post that may be helpful in storing your seeds in the freezer}.  Cold temperature will slow the seed ageing but just as important as cold is a constant temperature. Do not put the seed on the freezer door, which can have temperature fluctuations every time you open the freezer/refrigerator. Many scientists I worked with stored seeds in special -20C freezers. Seeds at the international seed bank in Norway on Spitsbergen Island are stored at -18C which is 0 F, a bit colder than a typical freezer. The idea is that the colder the temperature the longer the seeds could survive. If you don’t have access to an ultra cold freezer as a home hobbyist, your freezer or even refrigerator is fine. No matter where you store your seeds they should be placed in labeled containers, with the date on them so that you can keep track of time. This is also a good place to list other important tid bits like the specific traits the parent(s) of the seeds had to reference for breeding, like “Tall” “Tastes fruity” or “Quick to finish flowering” etc.
Second, keep your seed dry – the lower the humidity the less chance that microbes will attack and destroy the seeds, and the less likely that the seeds will break down physiologically inside. It might be a good idea to use a chemical desiccant if you have access to one.
Be mindful that seeds within and among different species will have different longevity. At Michigan State University, there was a professor Beal who in the 1890’s stored seeds of many different species of plants in containers. These containers were buried in secret locations all over the campus. One of my dissertation committee members had responsibility for the map of where the containers were stored around the campus. One of the last containers was dug up while I was at MSU. All seed were over a century old, and only one species of plant, Verbascum thapsus (common mullein) still had some seed germination. On the other hand, I have read reports of seeds found in peatlands germinating after centuries, but I think that is the exception rather than the rule.
No matter what you are growing, your seeds and clones will only last so long, plant breeding is the only way to get new plants. As I see it, you have two choices; you can do it, or pay someone else to. If you are interested in doing it yourself, please read the next several posts about plant breeding.

Good Growing!