Plant Propagation PLSC 368
Dr. Chiwon Lee
Carina De Luca
Potatoes are indigenous to the Andean regions of
Potatoes are indigenous to the Andean regions of
Potatoes are adapted to an array of climates and are utilized in many ways. There are cultivars developed for different environments and end uses. Because of the wide adaptation and many species, a vast genetic resource can be called upon for introgression of resistance to disease and insect pests, stresses, as well as improvement of quality traits.
The tuber is not only the principal mean for potato propagation, but also a major human food source. Potatoes are mainly propagated by vegetative methods (cloning). This is the primary commercial propagation method. Vegetative reproduction ensures a uniform crop, contraire to what would happen with sexual propagation. Sexual propagation of potato is accomplished by planting its “true seed”, but a high variability exist between this seed and that is why is not commonly used. However, sexual seed is becoming more and more popular; especially in places were disease pressure is very high and maintaining disease free seed is becoming a problem.
I. Asexual, vegetative or clonal propagation:
When potato growers talk about “seed” they are talking about the tuber and not the botanical or sexual seed. Potato tubers are actually a modified stem with approximately 70-75% content of water and a remaining 25-30% of dry mater. They have nodes or “eyes” from which the new growth begins. The new stems growing from each “eye” are called sprouts. Sprouts grow from the tuber after a period of dormancy after they are harvested, this varies largely between cultivars. After this dormancy is broken, sprouts grow and when planted, they give rise to the plant stems and from there all the vegetative part of the plant. Underground, lateral shoots called “stolons” are formed, from which the new tubers will be formed.
Vegetative seed can be either a whole tuber or a cut tuber. The standard seed piece used by growers is 2” by 2” or 2 oz.
Potato tuber cut to form seed pieces
Research has shown that a seed piece this size has the adequate amount of carbohydrates levels for shoot initiation and growth. If the tubers are cut, the usual procedure is to let the cut pieces to suberize or cure, for about 10 days. Suberization in tubers allows them to develop a corky layer around the seed piece that prevents the seed piece decay by the entrance of several kinds of pathogens.
Physiological age of seed
Is not the chronological age of the seed piece; instead, is the influence of the growing environment of the seed. Physiological age of seed is influenced by growing conditions, handling, storage and cutting procedures. Physiological age of the seed will have an impact on how the new crop grows.
• Rapid emergence
• More stems
• More tubers, smaller tuber size
• Earlier tuber initiation
• Earlier maturity
• Earlier senescence
• Less potential for high yield
• Slower emergence
• Fewer stems
• Later tuber initiation
• Later maturity
• Prolonged vigor of plants
• Higher final yield in a long season
It is very important to manage the physiological age of the seed because it has a big impact on how the new crop is going to look like and it will probably, along with many other factors, determine weather the crop will be of a high quantitative and qualitative value.
Other than seed age, there are some pros and cons when talking about vegetative reproduction, some of them include the fact that cloning assures genetic purity and product uniformity, it also favors high yields. Some of the disadvantages are that cloning favors disease spread (e.g. viruses, bacteria, fungi), and also a significant amount of storage space, transportation and heavy planting equipment is required.
II. Propagation by botanical or sexual seed:
Most potato cultivars produce fruit but some are pollen sterile or fail to ser fruit for other reasons. If fruit is established, they usually are small, up to 1.25 “in diameter and are green colored, resembling a small tomato.
The fruit contains the true seeds of potato plants, containing approximately 300 seeds per fruit. When the potato plant reproduces, usually through self-pollination, the chromosomes (along with the genes they carry) are randomly distributed to the seeds. Each seed will develop into a plant with unique characteristics. This is a process very useful in crop improvements in breeding programs, but its genotypic variation is of little value to growers because a new plant could be totally different to the mother plant and no uniformity would be seen in the field. Some of the advantages that true potato seed have are that they don’t carry any diseases and that seed can be stored in small places contraire to what happens with tubers.
III. Tissue Culture:
Tissue culture permits a very rapid propagation. Under traditional propagation, one tuber yields approximately 8 daughter tubers in one growing season, while with tissue culture, 100,000 identical plantlets can be produced in eight months, that when transferred to the field, could produce 50 MT of potatoes.
Each plant has a root system, leaves and terminal points or growth points. There is an apical meristem found at the apex of a potato stem and it also has lateral growth points. Each of these buds has a meristem which allows it to become a different plant.
The process of this technique is very simple. Disease free plantlets are grown in test tubes on a nutrient media. Each plantlet is cut into 3 to 10 nodal sections after 18-60 days. Each new cutting is planted in a new test tube. This can be repeated until the desired number of plantlets is obtained. Plantlets are then removed from the tubes and grown in sterile soil and let them complete their entire growth cycle. Tubers produced are collected and stored to later be sold to growers. This is also the process followed to obtain certified seeds. This first seed lot would be called “nuclear seed” and then after harvesting the product of this seed you get “Generation 1” (G1) and so forth.
Meristems have no vascular system, therefore are less prone to viral, fungal and bacterial infections. For this reason this method is used to maintain disease free seed stock, which can be then stored “in vitro” and be used when is needed.
A. Mosley, I. Vales, J. McMorran, S. Yilma. 2000. CSS 322, Principles of Potato Production. Available at http://oregonstate.edu/potatoes/CSS322WebNotes.html
Plaisted R. L. 1987. Potato (Chapter 11) subtracted from the book: Principles of Cultivar Development Volume
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Mills H. A. 2001. Vegetable crops: Potato, Solanum tuberosum L. University of Georgia. College of Agricultural and Environmental Sciences. Department of Horticulture. Available at: http://www.uga.edu/vegetable/potato.html
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S.L. Love, editors. 2003. Potato