From the magazine: No. 1 2016
Category: Specialist consultations
Thomas Bottner, Export Director of EUROPLANT Pflanzenzucht GmbH
Preparing seed material for the early potato season is a very responsible and difficult task. It is very difficult to obtain well-sprouted seed potatoes without special knowledge and the use of advanced technologies. We suggest paying attention to five factors that always influence the quality of potato germination.
First factor: Variety
Finding a potato variety that is ideally suited to climate conditions and growing technologies is not easy. And if you choose early potatoes, the production of which will require germination of tubers, the level of complexity increases: in this case, additional varietal characteristics must be taken into account. It is very important, for example, stability of seedlings and the ability of the variety to regeneration in case of damage and fragmentation of seedlings. The stability of seedlings mainly depends on the depth of the buds. The deeper the eye, the greater the stability of the seedling, thanks to this natural depression. Deep eyes are technically invulnerable, but unfortunately, they become more clogged with soil and lead to large waste during cleaning and processing, reducing the marketable yield. Therefore, in recent decades, visually attractive tubers with shallow eyes have been selected in breeding, which turned out to be counterproductive for the stability of seedlings.
No less significant for the variety and regenerative ability (that is, the ability of seedlings to germinate again after mechanical damage or breaking off during planting). Each potato grower can independently determine the regenerative ability of a potato variety or seed batch. To do this, it is enough to drive nails into the board and plant tubers on the sharp end (as shown in the picture), this way you can determine the differences between varieties or seed batches long before planting (Photo 1). Testing is best done at different temperatures to determine the most suitable conditions for regeneration. Slow regeneration should be taken into account when determining the optimal planting date. Varieties/lots with slow regeneration require particularly careful handling during planting and careful monitoring of soil temperature. Loss of seedlings during planting under suboptimal conditions and low temperatures affects yield.
Photo 1. Self-testing for the properties of varieties
Second factor: Warming up the tubers
The physiological processes of potato germination can be stimulated by heating. Basically, heating is required for varieties/lots that are in the dormant stage. Taking into account the physiological age of the tubers, heating is carried out at a temperature of 18°C for 7-14 days.
Before the season, it is important to take into account the condition of each seed lot. Varieties prone to germination must be restrained, and dormant varieties must be forced by heating the tubers. The current state of each seed lot can be determined by test germination (three weeks of storage in a dark room at room temperature).
Varieties prone to long-term dormancy (stimulate germination)
— Warm up to max. t 20°С
— Avoid direct contact of tubers with heated air (use heating hoses)
— Avoid stagnation of heat (air must circulate)
— Allocate separate rooms for germination of each variety
— Avoid temperature changes (help: thermometers)
— After heating, store the batch at low temperatures
Varieties prone to rapid germination (restrain germination)
— Germinate at low temperatures (3-5°C)
— Use low-heat germination lamps
Warming up should be carried out very carefully, making sure that all tubers are in the same conditions. It is necessary to avoid temperature changes, otherwise there will be grounds for uneven development of seedlings. The determining factor for this is the volume of the room: rising warm air should not accumulate in the area of the upper containers. Therefore, care must be taken to allocate sufficient space (to ensure free air circulation). If there is no special room, you can temporarily fence off the warming area using bubble wrap. Be careful: the film must not touch the last containers, otherwise there will be no buffer zone for the fan and rising warm air. This will cause heat to build up (Photo 4).
When warming up, you should pay attention to a sufficient supply of oxygen. Due to the heating of the room, the CO2 content in the air very quickly increases, and if the room is not ventilated (at least 2x15 minutes a day), the potatoes will suffocate (black core).
Photo 2. Same temperature of tubers
Photo 3. Unprofessional - the film lies on the potatoes
Photo 4. Different temperatures of tubers from different containers and storage heights
Recommendation: Heating without technical control and regulation is practically impossible. Temperature is measured using probe thermometers. If possible, check the temperature distribution in the storage facility with a thermal imager.
Third factor: Temperature
An important parameter for controlling potato germination is regulating the room temperature. To obtain the desired length of seedlings by the planned planting date, the individual temperature requirements of the variety should be taken into account.
In November-December, it is advisable to set the air temperature in a special room within 4-6°C. At this temperature, tuber germination can be delayed. Reducing the room temperature can be achieved by ventilating in the early morning hours.
Caution: at temperatures below 3°C, seedlings begin to die! In the absence of air ventilation in the room, a rapid temperature drop of several degrees is observed (Photo 6). In the worst case, due to the difference in temperature in the containers, the batch of potatoes will not germinate uniformly. The sprouts on the tubers will have different lengths, which will increase the risk of them breaking off during planting and, in turn, lead to uneven germination of the tubers. A ceiling fan with a temperature sensor will help to cope with the problem, which will ensure the necessary air circulation in the storage. This will ensure uniform temperature distribution among the containers.
Along with the air temperature, special attention should be paid to the floor temperature. At floor level in winter, a constant temperature is maintained within 4°C (Photo 5). If planting material is exposed to different temperatures for 50 days, this will lead to different stages of development in the process of germination of tubers. Each storage facility is individual, and therefore the germination of seed potato tubers requires special management. Regulating the temperature during germination is very difficult! The presence of temperature changes becomes noticeable with the naked eye when it is too late to correct something!
Photo 5. Cold reflection of the floor negatively affects the development of seedlings
Heating with a sharp increase in temperature is fraught with danger - even if the process lasts only a few hours. Any, even small, condensation creates ideal conditions for the development of silver scab and fusarium. Condensation can only be avoided by slowly raising the temperature. This requires high power heating and ventilation equipment. It is not enough to place a fan heater in the middle of the storage and turn it on for 20 hours: as the temperature rises, condensation will seep into the lower layers of the containers - and with it the silvery scab! For intensive air heating (below 20°C), it is better to use a fan that circulates air and controls the temperature using temperature sensors.
Fourth factor: Lighting
Along with temperature, the length of seedlings is significantly influenced by light. If you start lighting the tubers in a timely manner, it becomes possible to effectively influence the length of the seedlings. When does the favorable moment come? The safest time to connect the lighting is the day before the first seedlings appear in the eyes.
The basis for homogeneous lighting is a technique that must cover each container (360° potatolight; Photo 6).
Lack of lighting or its late connection are the cause of elongated seedlings (if the seedling has reached a certain length, this is an irreversible process).
Later, the connection of lighting is clearly visible in the seedling along the constriction line.
Why on the constriction? The seedling by nature seeks light: it begins to produce chlorophyll only in the light. In photo 7 the various constrictions are very clearly visible. In this case, the lamp hung low or the drawers were very high in the ceiling, or the lighting had not yet been connected at all. Both seedlings differ in the start time of illumination. In such cases, one should not expect simultaneous germination of tubers.
Photo 6. 360° - lamp for lighting potatoes
Photo 7. Reupholstery depending on the start date of lighting
Recommendation: Homogeneous lighting ensures homogeneous seedlings. The 360° germination lamp guarantees all the benefits of optimal lighting.
Fifth factor: Landing
The germination of tubers depends not only on the length of the seedlings. Success largely depends on planting technology and quality of planting. When planting, seedlings are inevitably subjected to mechanical stress.
When using incorrect planting equipment or poorly prepared planting material, significant breakage of seedlings is possible. Moreover, the percentage of losses is usually much higher than many people assume! Sprouts broken off during planting are the main problem with poor potato germination. Due to the mixing of damaged and broken shoots, different phases of regeneration are observed. These phases have a decisive influence on the beginning of tuber formation or on the size of the future tuber. Mechanical damage to sprouts or their breaking cannot be prevented (except for manual planting). It is believed that the longer the sprout, the higher the likelihood of damage. Already under the weight of the tuber’s own weight (about 50 g) and a free fall height of 30 cm, for a sprout with an area of about 1 mm2, - already a lot. Therefore, it is necessary for each tuber to “break in” before it takes on the burden of its weight with the sprout.
To check the tendency of sprouts to break off during planting, you should again perform a simple self-test: Simulate planting potatoes by dumping a box of sprouts onto a concrete floor. After this, collect the potatoes again in the box - the number of sprouts that have fallen off is obvious. Through such testing, the difference in the quality of sprouted tubers, the difference between varieties and storage batches, is clearly visible.
The most reliable method for planting a sprouted tuber in the soil without damage is still manual planting. Of course, it does not have great productivity and is very labor-intensive, but when testing germinated planting material it provides the best results. The germination process is completed only when the seedling, grown at great expense, is planted in the soil, and on the tuber, and not next to it.
Friendly shoots and high marketability of the crop for sale are all a merit of the successful germination of potato tubers.
Conclusions
Sprouting potato tubers is a complex process; any simple mistake can lead to losses. Therefore, it is very important that each of the above five influencing factors is considered separately. Due to increasing market demands, every manufacturer is called upon to achieve high yields. An objective view of the seed material, combined with appropriate experience and the specialized use of technical aids, will ensure long-term success in the germination of planting potatoes!