The Vigor of Seed Potatoes from Organic and Conventional Systems

Abstract

In the research carried out in 2018–2020 at the Plant Breeding and Acclimatization Institute, the vigor of seed potatoes from two production systems—organic and conventional—was examined. The characteristics of the tubers and the plants grown from them were assessed. It was found that seed potatoes from the organic system were characterized by features showing symptoms of weaker vigor, i.e., a shorter resting period, a smaller percentage of germinating eyes, a smaller mass of sprouts produced, and a shorter length of the longest sprout. The weaker vigor of seed potatoes from the organic system was reflected in the development and yield of the plants derived from them. It was expressed in weaker emergence, lower stem number, and smaller yield per plot. However, there were no differences in the yield structure. A large varietal differentiation was demonstrated for most of the studied traits. The differences in the vigor of individual cultivars were not related to the length of the growing season. The conditions prevailing in the research years had the greatest impact on the length of tuber dormancy, the percentage of germinating eyes, and the percentage of plant emergence.

1. Introduction

The vigor of seed potatoes is the sum of the properties that determine their physiological potential for rapid and even germination, good emergence, and proper plant development. From an agricultural point of view, vigor characterizes their future productivity. Therefore, there are three types of vigor: genetic, physiological, and ecological [1]. Such a division of vigor points to separate sources of its origin, but all of its forms cannot be separated, and vigor ultimately comes down to the physiological implementation of the genetic program under changing environmental conditions. The physiological vigor of the mother potato tubers depends primarily upon their physiological age [2,3,4,5]. There are several successive stages in the development of the potato tuber, such as rest, domination of the apical sprout, sprouting a few eyes, germination of a large number of eyes, and the tuberization stage in the sprouts.

For germination to occur, the harvested tubers must undergo a period of rest, i.e., a physiological slowdown. Prematurely harvested potatoes tend to have a longer resting period than those harvested when they are fully ripe. In physiologically younger seed potatoes, there is usually an enhanced apical dominance, which results in a smaller number of sprouts and stems [6]. Diversified germination of mother potato tubers is related to their physiological age, which is most influenced by storage conditions, mainly temperature. This is the most important factor influencing the physiological aging process of tubers. During their storage period from autumn to spring, increasing the temperature in the range of 2–20 °C accelerates the aging processes [3].

Seed potatoes become physiologically older the longer the time elapses from their initiation on the mother plant and the higher the ambient temperature. Conversely, they remain physiologically younger the shorter the time that elapses from their initiation on the mother plant and the lower the ambient temperature in the above-mentioned range. As the tubers age, their yield potential changes—first it increases, then it reaches the optimum level, and then it decreases. In extreme cases, when seed potatoes reach an advanced stage of development, the phenomenon of the production of daughter tubers directly on the mother tuber may occur, omitting the plant growth and development phase.

The vigor of seed potatoes depends not only on the environmental conditions, but also on the cultivar [7,8]. From the earlier description of changes taking place in the tuber, it could be concluded that early varieties with a short growing season will be characterized by a fast rate of physiological aging, and later varieties will be characterized by a slower aging rate. However, this is not necessarily the case. The physiologically rapidly aging varieties with a prolonged period of sprouting of seed potatoes are characterized by lower plant height, fewer stems, lower ground weight, and lower yield than physiologically slowly aging varieties. According to Caldiz [9] and Struik [10], the most important task in research on physiological age is to find a reliable and rapid diagnostic tool to assess the rate of physiological aging at different stages of the development of the mother tubers with the ability to predict the further aging process as a function of temperature. Unfortunately, it has proven to be too difficult to find features that could assess the physiological condition of tubers of a given variety under different environmental conditions and to predict future trends. It seems, however, that the use of modern molecular methods may allow for the assessment of the discussed physiological properties of tubers under various storage conditions.

As previously mentioned, the vigor of seed potatoes depends largely on the environmental conditions, including soil and climatic conditions, as well as the agrotechnical conditions in which seed potatoes grew. An increasing number of potatoes around the world are grown in environmentally friendly systems, including an organic system in which mineral fertilizers and pesticides are essentially unused. The yields obtained from these production systems are lower [11,12,13], and the commercial quality of the tubers is generally lower, i.e., the share of tubers with defects is generally higher [14], but the chemical composition and nutritional value of tubers is better, in most cases [15,16].

The question arises as to how cultivation in the organic system, without the use of chemical means of production, affects the vigor of seed potatoes and whether seed potatoes from the organic system differ in yielding potential compared to that of those from the conventional system. There is practically no research on this issue. Therefore, the aim of the work is to answer these questions.

2. Materials and Methods

A study was conducted in the years 2018–2020 on a light loamy sand at the Plant Breeding and Acclimatization Institute in central Poland. Potatoes were grown using the two systems—organic and conventional. The two systems differed regarding fertilization, weed control, and insect control practices (

Table 1. Agronomic inputs in the organic and conventional systems, Jadwisin, 2018–2020.

Crop Production Practice	Organic System	Conventional System
Fertilization	Manure-28 t∙ha−1 + mustard as a catch crop	4–5 t plowed rye straw + 1 kg mineral nitrogen per 100 kg straw N: 100 kg ha−1 P: 53 kg∙ha−1 K: 150 kg ha−1
Weed control	Mechanical tillage only	Mechanical tillage + herbicides (2 times per season): Linurex-1.8∙ha−1, Titus + Trend 60 g∙ha−1 + 0.5 L ha−1
Colorado potato beetle control	Biological insecticide Spin Tor 240 SC (Spinosad)2 times per season-0.15 L∙ha−1	Chemical insecticides (2 times per season): Actara 60 g ha−1 Apacz-40 g∙ha−1
Late blight control	Copper fungicides Miedzian 50, 3 L∙ha−1-2 times per season	Chemical fungicides (4 tmes per season): Ridomil 2 L∙ha−1, Revus-0.6 L∙ha−1, Ranman 0.2 L∙ha−1, Altima 0.4 L∙ha−1

).

Eight table potato varieties were chosen for this study, based on maturity class (

Table 2. Characteristics of potato varieties evaluated in organic and conventional production systems during 2018–2020.

Variety	Maturity Group	Origin
Justa	very early	Polish
Tacja	very early	Polish
Lawenda	early	Polish
Magnolia	early	Polish
Laskara	mid early	Polish
Lech	mid early	Polish
Mazur	mid early	Polish
Otolia	mid early	German

). All varieties were planted at the same time about 20 April. The plot size was 84 m² in three replications. The plants were grown with spacing 75 × 33.3 cm.

After harvesting (about 10 September) 20 even tubers (40–50 mm diameter) were collected from both plantations in 3 repetitions. The tubers were stored at room temperature (20 °C), in the dark, and with a relative air humidity of 80–90%. The length of the dormancy was monitored every 5 days. According to the findings of the Physiological Section of the European Potato Research Association, the end of dormancy was considered to be the date when 80% of the tubers of a given sample would produce sprouts 2 mm long under the above-mentioned conditions [17]. The length of the dormancy was counted from the zero date, i.e., 1 October. After dormancy, the tubers were stored under the same conditions until spring. One month before replanting in the field, all sprouts produced were broken off and their weight was weighed. The length of the longest sprout from each tuber was also measured. After the sprouts were broken off, the tubers were pre-sprouted in the light at 15 °C for 4 weeks. After this period, the sprouts produced were counted again. The seed potatoes prepared in this way were planted in the field on a conventional plantation. In the following years of research, i.e., the second and third years, all treatments performed in the conventional field were the same as in the first year.

During the growing season, the percentage of emergence in each combination and variety was counted. The stems of each plant were counted in full plant development. At the time of harvest, the yield of the tubers from each plant, as well as its structure, were determined, i.e., the share of tubers with a diameter of up to 30 mm, 30–60 mm, and over 60 mm.

The atmospheric conditions in the research years are presented in

Table 3. Total monthly rainfall and mean monthly temperatures during the vegetative growth period in the years 2018–2020 for Jadwisin.

	Total Monthly Rainfall (mm)							Mean Monthly Temperatures (°C)
Year/ Month	IV	V	VI	VII	VIII	IX	Sum	IV	V	VI	VII	VIII	IX	Mean
2018	21.7	43.4	41.0	75.2	60.6	30.9	272.8	13.2	17.6	19.1	21.2	20.8	15.8	18.0
2019	1.7	76.6	6.9	33.4	37.0	60.8	216.4	10.2	13.4	22.7	18.8	20.8	14.7	16.8
2020	5.6	65.3	113.8	40.4	120.7	51.8	397.6	8.8	11.6	18.7	19.0	20.1	15.5	15.6

.

Data Analysis

All of the experiments were repeated three times (years). Statistical analyses of the results were performed using Statistica software (StatSoft, Statistica 12 program). The effects of crop production system, variety, and years on the vigor of seed potatoes (length of dormancy, eye number, sprout number, % of sprouting eyes, sprout mass, length of the longest sprout, % of emergence, stem number, yield per plant, yield per plot, share of small tubers (%), share of middle-sized tubers (%), share of large tubers (%)) were evaluated using univariate analysis of variance (ANOVA) procedures. After verifying the homogeneity of error variance, all data across crop production system, variety, and years were evaluated using three-way ANOVA. The differences were determined using least significant difference analysis, with differences considered significant at p = 0.05. Testing of the significant differences in all parameters was performed by Tukey’s HSD post hoc test (α = 0.05). Statistical significance is reported in the tables and corresponding legends.

Microsoft Excel 2019 was adopted for data sorting and analysis.

3. Results

3.1. The Influence of the Tested Parameters on the Properties of Seed Potato Tubers

The analysis of variance showed the importance of variation in the varieties in relation to all the tested characteristics regarding the properties of the tubers, i.e., the length of the dormant period, the number of eyes per tuber, the number of sprouts produced, the percentage of germinating eyes, and the length of the longest sprout.

The production system significantly influenced the length of tuber dormancy, the percentage of germinating eyes, the mass of the sprouts, and the length of the longest sprout. The years of research had a significant impact on the length of the dormancy period and the percentage of germinating eyes. The significance of the interaction of varieties with the production system was recorded in relation to the length of the longest sprout (

Table 4. Sources of variation, ANOVA results, and levels of significance (p-values) for treatments affecting tested parameters—tuber features.

Source of Variation	Length of Dormancy	Eye Number	Sprout Number	Percent of Sprouting Eyes	Sprouts Mass	Length of the Longest Sprout
Variety	0.037 *	0.002 **	0.023 *	0.006 **	0.000 ***	0.000 ***
Production System	0.006 **	0.203	0.244	0.004 *	0.000 ***	0.019 *
Year	0.000 ***	0.080	0.570	0.014 *	0.088	0.563
Variety × Production System	0.982	0.974	0.544	0.422	0.016*	0.000 ***
Variety × Year	0.593	0.341	0.834	0.913	0.988	0.038
Production System × Year	0.091	0.091	0.242	0.176	0.806	0.944

* significant at α = 0.05; ** significant at α = 0.01; *** significant at α = 0.001.

).

As shown in

Table 5. The value of parameters characterizing tuber features in relation to variety and production system.

Production System	Variety	Lenght of Dormancy (Days)	Eye Number	Sprouts Number	Share of of Sprouting Eyes (%)	Sprout Mass (g)	Length of the Longest Sprout (cm)
Organic	Justa	32.6 a	6.5 a	4.2 a	66.7 a	2.8 ab	1.3 a
	Laskara	36.3 a	7.7 a	5.5 a	70.0 a	3.3 abc	6.7 a
	Lawenda	25.3 a	6.2 a	3.9 a	62.3 a	4.4 abc	3.7 a
	Lech	28.3 a	6.2 a	4.2 a	68.3 a	4.1 abc	4.6 a
	Magnolia	32.3 a	5.2 a	3.7 a	73.7 a	3.1 ab	3.0 a
	Mazur	33.3 a	7.0 a	4.9 a	70.0 a	3.3 abc	8.4 a
	Otolia	32.6 a	6.6 a	3.6 a	54.7 a	2.2 a	2.1 a
	Tacja	25.0 a	6.3 a	4.8 a	76.0 a	4.0 abc	3.3 a
Conventional	Justa	36.3 a	6.0 a	3.1 a	51.7 a	4.4 abc	3.2 a
	Laskara	46.0 ab	8.1 a	4.6 a	60.3 a	4.3 abc	5.9 a
	Lawenda	28.0 a	6.7 a	3.4 a	53.0 a	6.3 bcd	6.6 a
	Lech	30.6 a	6.8 a	4.2	62.0 a	6.0 bc	6.0 a
	Magnolia	38.3 a	5.3 a	3.7 a	69.3 a	6.9 cd	14.3 a
	Mazur	42.0 ab	7.7 a	6.0 a	78.0 a	4.4 abc	3.0 a
	Otolia	54.6 b	7.5 a	3.4 a	45 a	3.0 ab	3.3 a
	Tacja	33.6 a	6.2 a	3.2 a	51.3 a	9.7 d	39.0 b
Mean for variety	Justa	34.5 A	6.2 AB	3.7 A	59.2 AB	3.6 AB	2.2 A
	Laskara	41.2 AB	7.9 B	5.1 A	65.2 AB	3.8 AB	6.3 A
	Lawenda	26.7 A	6.5 AB	3.7 A	57.8 AB	5.4 BC	5.1 A
	Lech	29.5 A	6.5 AB	4.2 A	65.2 AB	5.1 ABC	5.3 A
	Magnolia	35.3 A	5.1 A	3.7 A	71.5 B	5.0 ABC	8.6 A
	Mazur	37.7 A	7.4 B	5.5 A	74.0 B	3.9 AB	5.7 A
	Otolia	43.7 B	7.1 B	3.5 A	49.8 A	2.6 A	2.7 A
	Tacja	29.3 A	6.3 AB	4.0 A	63.7 AB	6.8 C	23.5 B
Mean for system	Organic	30.8 A	6.4 A	4.3 A	67.7 B	3.4 A	4.7 A
	Conven tional	38.7 B	6.8 A	4.0 A	58.8 A	5.6 B	10.2 B

a, b, c, d (for interaction variety × system); A, B, C (for average values); mean values indicated by the same letters are not statistically significant at the 0.05 level, according to Tukey’s test.

, on average, for the varieties and years of research, the length of dormancy for tubers from the organic system was shorter than that obtained from the conventional system, at 30.8 and 38.7 days, respectively. The variety Lawenda had the shortest dormancy (on average for the production system and the years of research), while the Otolia variety exhibited the longest.

The number of eyes per tuber depended only on the variety. The following cultivars produced the greatest number of eyes: Laskara, Mazur, and Otolia. A significantly smaller number of eyes was recorded in the Magnolia variety. The number of sprouts per tuber also significantly depended only on the variety.

The percentage share of the number of sprouts in relation to the number of eyes depended on all the examined factors. In the organic system, more eyes grew into sprouts than in the conventional system. The smallest number of germinating eyes was recorded in the Otolia variety, and the highest in the Mazur variety. The mass of the sprouts was significantly higher in tubers from the conventional system. Otolia variety was distinguished by a significantly lower mass of sprouts. The greatest mass of sprouts was recorded in the Tacja variety. The length of the longest sprout was also greater in tubers from the conventional system, on average 10.2 cm for the conventional, and 4.7 cm for the organic system (Table 5).

3.2. Influence of the Tested Parameters on Plant Characteristics and Tuber Yield

Significant varietal differentiation was found regarding all the examined plant characteristics, i.e., the percentage of emergence, the number of main stems, the yield of tubers per plant, the yield of tubers per plot, and the yield structure, i.e., the share of tubers of various sizes in the yield. The production system in which the seed potatoes were grown influenced the number of plants grown and the number of main stems in the plant. The yield of tubers per plant and its structure did not depend on the production system.

The examined factors was not significant (

Table 6. Sources of variation, ANOVA results, and levels of significance (p-values) for treatments affecting tested parameters—plant features.

Source of Variation	% of Emergence	Stem Number	Yield Per Plant	Yield Per Plot	Share of Small Tubers (%)	Share of Middle-sized Tubers (%)	Share of Large Tubers (%)
Variety	0.003 **	0.000 ***	0.054	0.008 **	0.000 ***	0.000 ***	0.000 ***
Production system	0.000 ***	0.002 **	0.120	0.000 ***	0.180	0.652	0.586
Year	0.014 *	0.729	0.353	0.832	0.200	0.191	0.171
Variety × Production system	0.422	0.817	0.209	0.839	0.588	0.374	0.431
Variety × Year	0.913	0.794	0.423	0.677	0.933	0.204	0.233
Production system × Year	0.176	0.952	0.815	0.805	0.455	0.678	0.652

* significant at α = 0.05; ** significant at α = 0.01; *** significant at α = 0.001.

).

As shown in

Table 7. The value of parameters characterizing tuber features in relation to variety and production system.

Production System	Variety	Share of Emerged Plants (%)	Stem Number	Yield Per Plant (g)	Yield Per Plot (kg)	Share of Small Tubers (%)	Share of Middle-sized Tubers (%)	Share of Large Tubers (%)
Organic	Justa	57.7 ab	3.6 ab	1435.3 a	15.3 ab	1.9 ab	54.9 ab	43.2 ab
	Laskara	91.2 b	4.3 b	1160 a	20.9 ab	1.5 ab	54.8 ab	43.7 ab
	Lawenda	67.5 ab	4.3 b	1275.6 a	17.7 ab	1.7 ab	67.5 ab	30.8 ab
	Lech	79 b	4.5 b	1543.0 a	24.6 b	3.8 b	88.4 b	9.0 a
	Magnolia	20.0 a	1.4 a	1240.6 a	4.3 a	1.5 ab	38.7 a	59.9 b
	Mazur	65.7 ab	3.8 ab	1376.6 a	19.1 ab	2.1 ab	48.0 a	50.0 b
	Otolia	80.3 b	3.8 ab	1342.6 a	21.4 ab	2.8 ab	71.1 ab	26.1 ab
	Tacja	63.1 ab	3.4 ab	1291.0 a	16.4 ab	1.9 ab	48.0 a	50.1 b
Conventional	Justa	86.0 b	3.5 ab	1331.3 a	22,7 b	1.0 ab	46.1 a	52.8 b
	Laskara	95.0 b	5.2 b	1242.6 a	23.8 b	1.6 ab	60.1 ab	38.3 ab
	Lawenda	96.1 b	4.8 b	1466.0 a	28.5 b	2.5 ab	60.3 ab	37.1 ab
	Lech	95.0 b	5.3 b	1498.0 a	28.5 b	2.5 ab	69.6 ab	27.9 ab
	Magnolia	72.5 ab	2.8 ab	1234.3 a	17.9 ab	0.6 a	47.8 a	51.3 b
	Mazur	87.2 b	5.4 b	1418.3 a	25.9 b	1.5 ab	41.3 a	57.2 b
	Otolia	96.7 b	4.6 b	1309.0 a	25.3 b	2.6 ab	71.1 ab	27.2 ab
	Tacja	98.2 b	4.6 b	1217.7	24.0 b	2.0 ab	61.2 ab	36.9 ab
Mean for variety	Justa	71.8 AB	3.5 AB	1383.3 A	19.0 AB	1.4 AB	55.5 AB	43.1 BC
	Laskara	93.2 B	4.8 B	1179 A	22.3 AB	1.6 ABC	57.5 ABC	41.0 ABC
	Lawenda	81.8 B	4.6 B	1370.8 A	23.1 B	2.1 ABC	63.9 ABC	34.0 ABC
	Lech	87.0 B	4.9 B	1520.5 A	26.6 B	3.1 C	79.0 C	18.4 A
	Magnolia	46.2 A	2.1 A	1237.5 A	11.1 A	1.1 A	43.2 A	55.6 BC
	Mazur	76.5 AB	4.6 B	1397.5 A	22.5 AB	1.8 ABC	44.6 A	53.6 bC
	Otolia	88.5 B	4.2 B	1325.8 A	23.6 B	2.7 BC	71.1 BC	26.7 AB
	Tacja	80.7 B	4.0 B	1254.3 A	20.2 AB	1.9 ABC	54.6 AB	43.5 BC
Mean for system	Organic	65.6 A	3.7 A	1327.6 A	17.4 A	2.1 A	58.8 A	39.1 A
	Conventional	90.8 B	4.5 B	1339.7 A	24.6 B	1.8 A	57.1 A	41.1 A

a, b (for interaction variety × system); A, B, C (for average values); mean values indicated by the same letters are not statistically significant at the 0.05 level, according to Tukey’s test.

, the number of emerged plants depended on all the factors studied. A total of 65.6% of the seed potatoes from the organic system, and 90.8% from the conventional system grew into plants. The lowest percentage of emergence was recorded for the Magnolia variety (46.2%) and the highest for the Laskara (93.2%). Significantly more tubers grew into plants in 2018. Seed potatoes from the organic system produced fewer stems than seed potatoes from the conventional system. The smallest number of main stems was produced by the Magnolia variety, and the largest by the Lech variety.

The yield of tubers per plant depended neither on the production system nor on the variety. On the other hand, there were significant differences in the yield of tubers per plot. Due to the diverse number of plants in the plot, the yield of tubers from the plot on which organic seed potatoes were planted was 2 times than the yield from the plot for the conventional seed potatoes. The yield structure, i.e., the share of tubers of different sizes, depended mainly on the variety and was related to the share of medium and large tubers. The smallest share of medium tubers, i.e., with a diameter of 35–60 mm, was found in the Magnolia cultivars, and the highest in the Lech cultivar. In the case of tubers with the largest diameter, i.e., >60 mm, the relationships were the opposite (Table 7).

3.3. The Influence of Atmospheric Conditions on the Examined Features

As is shown in Table 4 and Table 6, the conditions prevailing in the study years significantly differentiated the length of tuber dormancy, the percentage of germinating eyes, and the percentage of plant emergence. The longest period of dormancy was shown by tubers in 2018 and the shortest in 2019. In the year 2019, the percent of sprouted eyes was significantly higher than in 2018 (

Table 8. Differentiation of tested factors depending on years.

Year	Length of Dormancy (Days)	Percentage of Sprouted Eyes (%)	Percentage of Emerged Plant (%)
2018	50.1 c	57.6 a	80.3 a
2019	21.4 a	68.8 b	76.5 a
2020	32.7 b	63.6 ab	77.8 a

a, b, c—Mean values indicated by the same letters are not statistically significant at the 0.05 level, according to Tukey’s test.

).

4. Discussion

The use of organic propagation material is obligatory, according to the current EU regulations for organic production. However, difficulties are frequently encountered regarding the availability, costs, or quality. The production of propagation material under organic farming conditions is more restricted regarding quality management compared to conventional production systems. For instance, field conditions for organic farming require a strong seed vigor in relation to competition with weeds [18,19].

Our research has shown a lower vigor of organic seed potatoes. This was expressed by a shorter dormancy period, a smaller percentage of germinating eyes, a smaller mass of sprouts, and a shorter length of the longest sprout. The inferior vigor of organic seed potatoes was reflected in weaker germination and poorer plant development. Plants grown from these seed potatoes were characterized by a smaller number of stems.

Although the yield of tubers per plant did not differ significantly from the yield obtained from seed potatoes from organic production, the yield calculated per plot was significantly lower. This was due to the smaller number of grown plants. The lack of differences in the yield of tubers per plant can be explained by the fact that the plots planted with organic seed potatoes had a low number of plants, which resulted in better conditions for the development of the plants that grew. There are no reports in the literature about the weaker vigor of seed potatoes coming from the organic system, but taking into account the agrotechnics in force in this production system, it can be assumed that it will be worse. Obviously, the organic system does not use any chemical means of production, i.e., mineral fertilizers and pesticides. The lower amount of nitrogen supplied (only organic), as well as the weaker protection of plants against diseases and pests, shorten the growing season, drying the plants up more quickly. In turn, this shortens the dormancy period of the tubers and accelerates the physiological processes taking place in the tubers, which contributes to faster aging [9,11,20,21,22].

The varietal differences shown confirms the results of previous research on this issue [8,22]. As mentioned before, the vigor of seed potatoes depends not only on the environmental conditions, but also on the variety. It is generally believed that varieties with a shorter growing season have a faster rate of physiological aging and weaker vigor when stored under the same conditions. In our research, the shortest resting periods were found in the early Lawenda and Tacja varieties, as well as in the mid-early variety Lech. The smallest percentage of germinating eyes was recorded for the Otolia variety, which was characterized by the longest dormancy. The aforementioned theory is confirmed by the very early variety Tacja, in which both the mass of the sprouts and the length of the longest sprout were the greatest.

The described varietal differences should be reflected in the response of plants to field conditions. The worst variety in this respect was the early variety Magnolia, in which only 46.2% of seed potatoes grew into plants, and this variety did not show signs of rapid physiological aging. The Magnolia variety also produced the fewest number of stems and the lowest yield per plot. On the other hand, the mid-early variety Otolia fared very well. The yield structure was a varietal feature. The Magnolia and Mazur varieties showed the highest proportion of large tubers, regardless of the production system from which the seed potatoes came.

Diversified climatic conditions in the years of the study varied the length of dormancy to the greatest extent. The length of the dormant period of tubers is a varietal feature and may be perceived as an advantage or a disadvantage, depending on the climate. Under temperate climate conditions, where there is only one potato harvest, a long dormant period is an advantage because the varieties with long dormancy store more easily, there is less tuber weight loss, and the tubers can used later in spring [23,24]. In climates with 2 or more potato harvests, a long dormant period is a disadvantage because tubers must be interrupted for a second time to germinate, and this is not always easy [25,26]. In the climatic conditions of Poland, a short resting period is a disadvantage. The shorter dormancy rate for seed potatoes from the organic system remains a disadvantage here.

In Poland, most varieties most often end their dormancy between the beginning of October and the beginning of January, but the weather conditions during the growth of plants largely affect the length of this physiological phase [11,20]. In dry and warm years, dormancy is generally shorter than in cool and humid years. This has not been confirmed in every case in our research. The tubers had the shortest dormancy in 2019, in which the amount of rainfall was the lowest, but the longest in 2018, which was drier than 2020. In 2018, the dormancy was the longest and the percentage of germinating eyes was the lowest.

5. Conclusions

The seed potatoes from the organic system were characterized by weaker vigor—a shorter dormancy, a smaller percentage of germinating eyes, a smaller weight of sprouts produced, and a shorter length of the longest sprout. The weaker vigor of seed potatoes from organic farming was reflected in the development and yield of plants derived from them—weaker emergence, lower stem number, and lower yield per plot. A large varietal differentiation was noted for most of the studied traits. The differences in the vigor of individual varieties were not related to the length of the growing season. The weather conditions had the greatest impact on the length of tuber dormancy and the percentage of germinating eyes.