B.S. Biotechnology, University of Wisconsin-River Falls
When trying to grow that huge Atlantic Giant pumpkin, there are two subjects that ultimately determine how big that pumpkin is going to be: environmental factors and genetics. Environmental factors include watering, fertilizing, temperature, sunlight, etc. These are all aspects of gardening that the grower has some control over. Genetics on the other hand is a little trickier, often times unpredictable and far less understood. This article will shed some light on the basics of genetics as it relates to Atlantic Giant pumpkins.
A pumpkin plant produces female flowers, which contain hundreds of ovules (eggs). It also produces male flowers, which produce pollen (sperm). Reproduction in plants, like animals, involves the uniting of an egg and a sperm to produce offspring. In the case of pumpkins, they produce seeds. One pollen grain + one ovule = one seed. Each pumpkin will produce many hundreds of seeds.
Each seed contains it’s own unique code which dictates all aspects of the future pumpkin’s growth. This code is called DNA. DNA is organized into genes. A gene controls one specific aspect of the pumpkin’s growth. One or more genes work together to form a trait. Color, size, and shape are considered traits.
Confused yet? Hopefully not because it gets thicker yet. There are many variations to a gene, which are termed alleles. Alleles are what make us, and pumpkins, all unique. For example, green, orange, red and yellow are all separate alleles for the “color” gene in pumpkins.
When the sperm and the egg unite, they combine their DNA to form a complete seed. The sperm and the egg each contain one allele for every gene (there are thousands) in the pumpkin’s genome. When the two alleles combine, the plant has a way of deciding which of the two alleles will be used or “expressed”. This is termed dominance and recessiveness. A sperm or an egg can contain either a dominant or a recessive allele for any gene, depending on what the parent plant originally gave it. A dominant allele will in effect shut off the recessive allele, thereby allowing the dominant allele to be expressed.
In pumpkins, orange color is a dominant allele, and green color is a recessive allele. If the egg contains the orange allele and the sperm contains the green allele, the orange color will be expressed, because it has dominance over the recessive green allele. The only way to produce a green pumpkin is if both the egg and sperm contain the recessive green allele.
One final point to keep in mind is that the pollen fertilizing the female flower has no effect on the growing pumpkin. The DNA contained within the pollen is passed on to the seed of the pumpkin. Therefore, the traits exhibited by a growing pumpkin are the direct result of the female’s parents. When making a cross, you are actually preparing the genetics of the next generation of pumpkins!
If you have ingested and understood the previous paragraphs, congratulate yourself. Some of the concepts are hard to grasp, but in the end will pay off. Hopefully this will be the jumpstart you needed to dive into more complex issues concerning AG genetics and it does get much more complex than this!!
Joe can be emailed here: Joea@pharmasan.com