Propagation techniques for potato planting materials

Photo by Markus Spiske from Unsplash.

Filipinos may be rice-eaters, but potatoes are still a frequent part of their diet. It is a common ingredient in many tomato-based dishes like kaldereta and menudo, as well as soups like nilaga. Outside Filipino cuisine, the potato is a common side dish offered in many fast food restaurants. One can enjoy it as french fries, mashed potatoes, or hashbrowns. 

In 2017, the local demand for potatoes was 380,333 metric tons. The problem is that a big percentage of this demand was fulfilled through imports, with only 31.98% of the local demand supplied with local sources.

One of the contributing factors to the low rate of local production is the limited supply of certified disease-free planting materials. The Department of Science and Technology (DOST) has been working to address this gap through the Potato Research and Development Center.

To help fulfill the demand for planting materials, researchers have been studying alternative propagation techniques such as micropropagation, microtuberization, and seed production via drip system and aeroponics.

To share what they have learned using these techniques, program leader Cynthia Kiswa from Benguet State University discussed these methods in a webinar organized by the Philippine Council for Agriculture, Aquatic and Natural Resources Research and Development (PCAARRD) on August 11, 2022.

Producing apical cuttings via micropropagation

Regrowing plants from shoots or cuttings allows people to multiply a plant without needing to sow a seed. This is a common practice among gardeners, especially those looking to reduce their kitchen waste. Instead of throwing away vegetable scraps, they can be reused to regrow a plant in a process called vegetative propagation.

Micropropagation takes this a step further by vegetatively regrowing plant parts in sanitized conditions. Doing so eliminates viruses, bacterial wilt, and potato cyst nematodes, which otherwise cannot be eliminated by pesticides.

Micropropagation starts with the meristem, a plant tissue where plant cells divide. The meristem can be specifically found in parts of a plant that are actively growing such as shoot tips, roots, cambium, and leaf nodes.

For propagation purposes, the meristem is extracted from shoot tips. Though the meristem may be taken from an infected plant, the absence of vascular tissues in the meristem ensures that it is free from the disease.

Propagators use a mother plant to acquire a steady supply of meristems. These are then grown in test tubes with a culture medium to support their growth. Survival of meristems is generally low, with less than 50% of meristems surviving. For this reason, propagators use what is called a thermotherapy growth chamber where the plant is stored for at least one month at a temperature of 32-37°C.

After a month, the plant is tested for diseases using a double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISAY) kit. Plants are usually only tested once but the mother plant is tested every month as part of the certification requirements of the Bureau of Plant Industry (BPI).

Once the plant tests negative for diseases, it can now be planted as an apical cutting, a term used to describe a rooted cutting grown from tissue culture. Through micropropagation, a potato shoot is able to multiply fivefold per month. At this rate, a single shoot can yield 125 copies in just three months. 

Producing microtuber seeds via microtuberization

Another propagation technique, which takes micropropagation one step further, is a process called microtuberization. This involves the use of a plant grown from tissue culture to produce microtuber seeds. Unlike apical cuttings, microtuber seeds do not require acclimatization before planting. Being seeds, another advantage is that they are easier to store and transport.

This process starts by cultivating a microplant grown from tissue culture in liquid media for a month. The researchers recommended limiting the number of microplants per container to three if test tubes are being used and 15 for Erlenmeyer flasks.

The plant is also irrigated with another medium to induce the growth of microtubers. Researchers found that a tuberization media composed of more than eight percent sugar yields bigger-sized tubers. 

To help the plant develop its microtubers, it is stored in a dark area at a temperature between 15-22°C. It takes 1.5-2.5 months for microtubers to initiate depending on the potato variety. 

For their trials, the researchers used raniag, cosima, benguetta, igorota, granola, and fina varities. The average number of microtubers produced per plant was one to two with each weighing between 0.7-3 grams.

The researchers noted that before the microtuber seeds are planted, they have a dormancy period of 17-30 days, which is shorter compared to microtubers harvested from conventional methods.

Seed production via drip system and aeroponics

Farmers may also opt to use actual tuber seeds as planting material. To enhance the production of tuber seeds, the researchers opted to experiment with a hydroponic drip system and aeroponics.

Both systems start with apical cuttings. For the drip system, the cuttings are planted in a medium composed of a 3:1 mixture of carbonized rice hull ash and alnus compost. 

The plants are nourished through emitters which trickle a nutrient solution and water at a scheduled phase.  This allows propagators to use 90% less water which would have otherwise been used if the conventional method was used.

For their aeroponics system, roots are hung mid-air underneath a seedbed panel board. Nutrients are misted to the roots via a pre-programmed hydro-automizer. 

The frequency of misting during the first 20 days is 15 seconds every two minutes. After this period, the frequency is reduced to 30 seconds every five minutes. The reason for this is that as the plant matures, it will develop more roots that could help hold the droplets.

The researchers conducted a trial to see the effectiveness of both systems. The drip irrigation system yielded 18,925 tuber seeds, three times more productive than the conventional method which only yielded 5,844. However,  the aeroponics system only yielded 5,707 tuber seeds. This was attributed to two power outages during the early vegetative period of the plant — a clear limitation that can be premeditated by having a standby power generator.

Effectiveness of propagation techniques

According to Kiswa, they conducted a tech demo involving 30 farmers from Benguet and 30 farmers for Mountain Province to show how effective these propagation techniques were. 

Prior to the implementation of these methods, the farmers only yielded 15 tons of potatoes per hectare of land. But by using planting material derived from the new propagation methods, the farmers harvested around 25-42 tons per hectare, which translated to a 60-180% increase in net profit.

This demonstrates the value of research-driven agriculture. If this is matched with capacity-building programs to make these technologies more accessible for farmers and propagators, this will likely improve overall potato production throughout the country.

The information provided here was from a webinar entitled “Enhanced production and management practices for potato” by PCAARRD. The webinar was partly led by Cynthia Kiswa, program leader of DOST’s Potato Research and Development Center. 

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