True Potato Seed

True Potato Seed (TPS) is the actual botanical seed produced by the potato plant (Solanum tuberosum). Found in tiny seed balls resembling tomatoes, TPS is occasionally formed after the potato has finished flowering (Figure 1). Potato crops are usually planted from the potato (or tuber) itself, but planting from TPS has several advantages.

Firstly, while TPS can be challenging to obtain, it is far less likely to harbour disease. In fact, only one disease (Spindle Tuber Virus) has been found in TPS, while tubers can host bacterial wilt, late blight, and many other diseases affecting the commercial potato industry. More importantly, the peculiarities of potato genetics cause plants grown from TPS to be markedly different from the parent plant and from each other. This diversity helps ward off incidences of plant disease while offering gardeners an opportunity to develop their own varieties.

Figure 1. TPS forms immediately after flowering.

The potato plant contains a wealth of genetic resources. While containing only 12 chromosomes, potato varieties can have multiple copies of these chromosomes. Cultivated varieties, for example, have four copies, for a total of 48 chromosomes.

When the potato plant reproduces, usually though self-pollination, the chromosomes (along with the genes they carry) are reshuffled, distributing themselves randomly to the seeds. Each seed will develop into a plant with unique characteristics. Some will have red tubers, others will demonstrate excellent disease resistance. Some will be worth growing out for generations, while others will grow poorly and have to be discarded.

TPS is collected and saved in a manner similar to that used to save tomato seeds. When the seed balls are green and soft to the touch, they are removed and cut in half. The seeds are then squeezed out into a shallow container, covered with water, and allowed to ferment for three days. They are then removed, washed using a sieve, and allowed to air dry.

TPS is usually stored in a cool, dry place for about eight months before planting them indoors into trays and transplanted out to the field (Figure 2). Before planting out, the seeds are usually treated with plant growth hormone. This, along with the fermentation process, helps to ensure proper germination.

Figure 2. TPS transplant.

Beginning in June 2004, we will plant out approximately 300 true potato seeds obtained from Dan O'Brien, one of our Home Garden Project participants, in an effort to develop new potato varieties adapted to urban growing conditions. We will be selecting for disease resistance, tuber size and flavour, and days to maturity. Highlights are outlined further below:

Update for August 7, 2004

The Group 1 seedlings have been transplanted into a test plot at the Gorsebrook Community Garden.
2 of these died within two days of transplanting.
Of the 15 Group 2 seedlings, 5 have failed since the last update.

Update for September 1, 2004

11 Group 1 seedlings are flourishing at the Gorsebrook Community Garden. 4 died since transplanting in late-July.
As the gardening season is drawing to a close, it was decided that the Group 2 seedlings should be abandoned.
The 2004 trials will now focus on the remaining 11 seedlings, which have established themselves well.

Update for October 11, 2004

To extend the growing season, a cold frame is now covering the test plot.
A cold snap, followed by a warm period, has caused many of the potato plants to develop blight-like symptoms on the foliage.
Many of the plants have developed potatoes, however, and all will be harvested at the end of the month.

Update for October 22, 2004

All potatoes have been harvested. As expected, tubers differ widely between plants.
Measurements for a number of physical characteristics were noted, including foliage cover, leaf size, number of tubers, etc.
As the tubers may not hold up under winter storage, the tubers will now be planted indoors under grow lights and allowed to form new plants asexually.
The next generation of tubers will then be planted into the field in the spring.

The CIP (Centro Internacional de la Papa) or in English, the International Potato Institute, is an excellent resource for information on the potato crop. This site outlines current research on TPS and its potential for use in the Third World.