Thursday, April 28, 2011

Below the Soil Surface

Fig. 1  Volunteer potato plant.
Ever since I planted my first potato crop in my garden, volunteer potato plants became a normal occurrence every spring.  No matter how much I'd try to look for all the tubers at harvest time, there would always be some tubers left behind.   As a general rule, I rarely use the same area in my garden for the same crop two seasons in a row.  In other words, I practice crop rotation.  The result of this is that some of the weeds that I have to remove from my garden before planting my spring crops are volunteer-potatoes (Fig. 1).   Sometimes when I pull them out of the ground they already have new potatoes (small and immature tubers) which when boiled and buttered make a treat for my kids.

When I was pulling the volunteer potatoes, I saw one that I could use as a visual aid for something I'd like to talk about - the parts of a potato plant that directly affects its performance.
 Parts of a Potato Plant: Underground (Part One)

Fig. 2 Parts of a growing potato plant.

Mother tuber is the seed tuber that was planted and where the new crop has grown from.  My former professor, Peter Vander Zaag, used to say that when a healthy seed tuber is planted, it is likely that it will remain till harvest time as a mother tuber.   Why it is called a mother tuber-- I'm guessing that it is because it has had the chance to reproduce.  :)  A firm and healthy mother tuber at harvest time indicates that the early growing conditions of the crop was  favorable allowing the new plant to shift from being dependent (drawing energy from the mother plant), to independently producing energy (through photosynthesis) before the energy from the mother tuber is depleted.

The mother tuber in the picture (Fig. 2), being a volunteer potato, was situated close to the surface of the soil.  It was exposed to a larger array of pests as indicated by the presence of holes on  the tuber. 

Fig. 3.    Stolons develop underground; lateral stems develop above ground. 

Fig. 4.   Sprouts on the seed tuber corresonds to the stems of the potato plant.

Main stems of potatoes grown from tubers are those that directly grow from the mother tuber. The sprouts (Fig. 4) on the seed tubers eventually grow into stems (Fig. 3). Stems that grow from the main stems are called lateral stems. The stem grows above ground but it has an underground section which is consist of the stolon, tuber, and roots. The length of this section of the stem is a function of planting depth and hilling-up. The greater the distance between the mother tuber and the top of the soil the more internodes will there be
The stems are generally green but the buried section is white (Fig. 2 and Fig. 3). Depending on species the stems could also be purple or reddish brown. 
Stolons are underground lateral stems (branches). They are easily identified as being thick white long structures arising from the nodes that are covered with soil (Fig. 5). Under favorable conditions, the apical end of the stolon eventually swells and develops into a storage organ called tuber. This stage is technically known as tuber initiation (Fig. 5). When the apical end of the stolon is exposed to light, it starts to produce chlorophyll and functions as a normal lateral stem or branch (Fig. 3).  One stolon potentially produces one tuber - hence the number of stolons in one plant determines the number of tubers produced.  
Fig.  5   Tuber initiation - apical ends of stolons developing into tubers.

Nodes are the points on the stem where buds, lateral branches, and  leaves originate.  In the case of the underground part of the potato, it is the point where the roots and stolons arise.   The space between nodes on the stem is called internode.  Planting deep enough to allow more nodes below the soil surface helps increase root and stolon formation.

Roots.   Potatoes that are grown asexually (from tubers) develop adventitious roots.  The potato plant has a root system that seem unsubstantial (Fig. 2) and growing superficially during its early growth stage [1].   Maintenance and conservation of soil moisture is important for this crop.   For small gardens, mulching is a practical management practice to take into consideration.    

Understanding the growth habits of plants help gardeners choose appropriate management practices for their crops.


HolleyGarden said...

Great info! Loved the picture where you name each part.

Helen Lewis said...

HolleyGarden --
Thanks for visiting my blog. I intend to talk more about potatoes as I follow my plants grow.

Desperate Gardener said...

Wow amazing pictures, and very informative!

Bom said...

Great information Helen! I'm learning so much from you. Still hesitant to try and plant my own potatoes but getting more confident with each post of yours that I read.

sbo said...


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