Cross Pollination in Plants
Cross pollination is when one plant pollinates a plant of another variety. The two plants’ genetic material combines and the resulting seeds from that pollination will have characteristics of both varieties and is a new variety.
Sometimes cross pollinating is used intentionally in the garden to create new varieties. For example, a popular hobby is to cross pollinate tomato varieties to attempt to create new, better varieties. In these cases, the varieties are purposefully cross pollinated. Other times, cross pollination in plants occurs when outside influences, like the wind or bees, carry pollen from one variety to another.
Many gardeners are afraid that the plants in their vegetable garden will accidentally cross pollinate and that they will end up with fruit on the plant that is sub-standard. There are two misconceptions here that need to be addressed. First, cross pollination can only occur between varieties, not species. So, for example, a cucumber cannot cross pollinate with a squash. They are not the same species. This would be like a dog and a cat being able to create offspring together. It is simply not possible. But, cross pollination can happen between a zucchini and a pumpkin. This would be like a Yorkie dog and a Rottweiler dog producing offspring. Odd, but possible, because they are of the same species. Second, the fruit from a plant that is cross pollinated would not be affected. Many times you’ll hear someone state that they know their squash cross pollinated this year because the squash fruit look odd. This is not possible. Cross pollination does not affect this years’ fruit, but will affect the fruit of any seeds planted from that fruit. There is only one exception to this, and that is corn. Ears of corn will change if the current stalk is cross pollinated. Most cases where the fruit looks odd happens because the plant is suffering from a problem that affects the fruit, such as pests, disease or nutrient deficiencies. Less often, odd looking vegetables are a result of seeds grown from last year’s cross pollinated fruit. Normally, this is more common in seeds that have been harvested by the gardener, as commercial seed producers take steps to prevent cross pollination. Cross pollination in plants can be controlled but you only need to worry about controlling cross pollination if you plan on saving seeds.
Types of Cross Pollinations
Abitoic pollination is a process where the pollination is carried out without the involvement of other organisms. About only 10% of plants are pollinated without animal agents.
Anemophily is the most common form of abiotic pollination, it is pollination by wind. The flowers that are pollinated by wind show the following characters:
• They are usually unisexual flowers.
• Stamens are exposed freely with versatile anthers.
• The pollen grains are light, smooth, dry and not easily wetted by rain.
• Pollen are produced in enormous quantities.
• The stigma is large and well exposed to receive the pollen grains.
• The flowers are small, inconspicuous with no color, odor or nectar.
Examples of wind pollinated plants are coconut, palm, maize, grasses etc.
Hyrdophily is the pollination by water and it occurs in aquatic plants as they release pollens directly into the surrounding water medium. Not all aquatic plants are pollinated by water, most of them bear flowers above the water surface and are pollinated by wind or insects.
Biotic pollination is the process of pollination that requires pollinators like some organisms that transfer the pollen grain from the anther to the receptive part or the stigma of the carpel or pistil.
Entimophily or Insect Pollination
Entimophily is the pollination carried out by insects. This process of pollination occurs in plants where they have colored petals and a strong odor to attract insects like bees, wasps and some ants, beetles, moths and butterflies.
The insects visit flowers in order to collect nectar, edible pollen, during this visit the pollen grains gets dusted on the body. When the insect visits the flower the body brushes against the stigma and transfers the pollen to bring about pollination.
Example: Rose, Poppy, etc.
Some features seen in insect pollinated flowers are:
• The flowers are large, and brightly colored.
• The flowers usually have pleasant fragrance and sweet nectar.
• The pollen grains are usually rough and sticky and they show spiny outgrowths.
It is the pollination performed by vertebrates like birds and bats. Plants that get pollinated by bats and moths are usually have white petals and a strong scent. Plants that are pollinated by birds usually develop red petals and rarely have any odor.
Example: Species of Arctium (burdock), Acaena and Gallium aparine
Ornithophily or Bird Pollination
Humming birds, sun birds and honey eaters are common bird pollinators. Bird obtain nectar from flowers. Flowers that are pollinated by birds have funnel shaped or tubular corollas and are brightly colored. The floral parts of these plants are leathery and produce large amount of nectar and pollen grains which are sticky.
Chiroperophily or Bat Pollination
Pollination by bats happens in the tropics. Bats visit flowers that are large and that emit strong odor. The flowers pollinated by bats produce more nectar and have large number of stamens.
Anthropophily is pollination performed by humans, it is usually artificial pollination used in hybridization techniques.
Open Pollination is the pollination performed by insects, birds, wind or other natural mechanisms. Open pollination ensures that all seeds of a crop are descended from parents with known traits and have desired traits. In open pollination the breeding is uncontrolled and the pollen source is unknown it may result in plant variety that may vary widely in genetic traits. Open pollen may increase biodiversity. Bigger challenges in open pollination is maintaining the strain by avoiding pollination by introduction of pollen from other strains.