1. Introduction
Maize is one of the world’s most important agricultural crops, forming the basis of many food products, biofuels, and industrial materials. According to the World Health Organization, in 2023, the world’s maize acreage was more than 190 million hectares, and global maize production reached a record 1.2 billion tons [1]. In Poland, maize occupies about 1.2 million hectares, and its national production has been estimated to be about 9 million tons per year [1]. Maize is an important component of Polish feedstuffs and is also used in the production of biogas and biofuels, which increases the importance of efficiently processing this raw material. A milestone in the cultivation of this species was the application of heterosis, which enabled a dynamic increase in the yield of new hybrid varieties [2,3,4]. This phenomenon was first commercially exploited in maize to develop the first high-yielding hybrid cultivar (i.e., double-crossed hybrid maize: Funk 250) in 1922 [5,6]. In commercial production, hybrid maize seeds predominate, and are produced as single crosses (SCs), double crosses (DCs), and three-way crosses (TCs) [7]. SC hybrids are known as the most productive and uniform, but are also the most expensive because both parents are inbred lines. Double-crossed (DC) hybrids are more affordable, as both parents are single crosses. TC hybrids are derived by crossing three lines: first, A is crossed with B; then, in the following year, AB is crossed with a paternal line, C. These hybrids are more efficient in terms of seed production; hence, their seeds are usually cheaper. They are characterized by a lower heterosis effect (due to double crossing), but are more malleable and can better adapt to changing growing conditions [8]. In terms of their germination capacity, hybrids also have a higher seed value than their parental forms [7].
Analyses of seed quality, depending on the genotype, the physical properties of the seed, and its reaction to the environment, may contribute to more efficient maize seed production, thus increasing the productivity of this species. However, studies in this direction are needed [7,8].
At present, it is recognized that the variety is the key element that determines the obtained yield in the cultivation of this species, regardless of the region of the world [8,9,10,11,12]. To optimize the potential of a variety, it is necessary to take into account not only the habitat conditions, including the soil and weather conditions [8,13], but also the agrotechnical conditions [14]. These include the appropriate preparation of seeds in a homogeneous batch, which is achieved through seed fractionation [15]. Fractionation is a procedure that refines seed material, obtaining seeds that are uniform in size and shape, which enables more precise sowing [16]. Seed breeding and production companies commonly use the seed fractionation process.
The classification of seeds into small, medium, and large fractions depends on the thousand-kernel weight and, therefore, on the endosperm content, which is used in the process of germination of the embryo. Large seeds are characterized by a higher germination capacity under field conditions, and the resulting seedlings generally have a higher weight compared to those obtained from small seeds [15]. A similar trend was observed by Dalapo and Modi [17], who also found that the vigor index was higher in small and flat seeds compared to large and round seeds.
The size and weight of maize kernels are important agronomic traits determined by the interaction of genetic and environmental factors, which have a direct impact on the improvement of maize yield [12,18]. The few studies on this topic have indicated that smaller seed fractions lead to faster seedling emergence than large fractions [16].
The primary storage organ in maize seeds is the endosperm, which provides nutrients and energy to the embryo while promoting seed germination and further seedling development [19]. The physical properties of seeds, including color and seed size, may also increase their susceptibility to infestation by Sitophilus species, which can decrease their quality [20]. Seeds and their quality are important elements for increasing plant productivity. To date, there have been few studies in the literature on the effects of seed quality and fractionation, particularly regarding assessments of the seed vigor, plant growth, and seed yield of three-line hybrid maize.
The purpose of the present study is to holistically determine how classified seed fractions of maize (based on the thousand-kernel weight) affect the differences and possible changes in the initial germination and seedling development under different vigor tests and temperature regimes; plant growth under field conditions; and, ultimately, seed yield and its components.
2. Materials and Methods
2.1. Experimental Design and Sample Collection
A study on ‘Lokata’ maize (FAO 220) was conducted from 2013 to 2015 at the Department of Agronomy in the seed laboratory and the field at the Research and Education Centre Gorzyn (Swadzim branch, Poland, 52°26′ N; 16°45′ E), which is part of the Poznan University of Life Sciences. The experiment was designed as a one-factor trial using a randomized complete block design with four replications. The research factor was the seed fraction isolated based on the thousand-kernel weight: I—small (244 g); II—medium (296 g); III—large (334 g); IV—very large (396 g).
2.2. Laboratory Experiments
Seed material from the same year (2012) was used in all years of this research. The seeds were obtained from one batch of seeds that were fractionated for commercial purposes and packed in original seeding units by the seed producer Malopolska Plant Breeding Kobierzyce. The seeds were stored under controlled conditions at 6 °C and 60–65% Humidity. The seeds were treated with a fungicide containing the active substances carboxin and thiuram. During the three-year study period, no significant differences were noted in seed quality based on storage. Therefore, this study took into account the average results of the study years. The average germination capacity values for the seed fraction were 98% in 2013, 96% in 2014, and 97% in 2015.
Seed value was assessed according to ISTA [21] methods and included the first count (germination energy), the final count (germination capacity), the percentage of abnormally germinating seeds, and the percentage of healthy non-germinating seeds.
Seed vigor was determined using the seedling growth test (SGT), the seedling growth rate test (SGRT), the conductivity test, the cold test, and the radicle growth (RE) test [21,22]. The seedling growth test consisted of placing 25 seeds in a roll of filter paper, with 4 repetitions. The blotting papers were moistened with deionized water and placed in a thermostat at 20 °C. When a germination rate suitable for the species was achieved, the length of the normally germinated seedlings was measured in cm, and the average seedling length per roll was determined.
The SGRT was conducted after completion of the SGT. This consisted of drying the seedlings normally germinated in each roll for 24 h at 80 °C, and then determining the weights of single seedlings (mg/seedling).
The conductivity test was carried out using an Elmetron CC-551 microcomputer conductivity meter (Elmetron, Zabrze, Poland). A total of fifty seeds from each fraction, with 4 replicates (weighed to the nearest 0.01 g), were placed in 400 cm3 beakers, each containing 250 cm3 deionized water. The seeds were left in a thermostat for 24 h at 20 °C before measuring the conductivity.
The cold test consisted of sowing 50 kernels from each combination, with 4 replicates, on rolls of blotting paper using non-sterile soil from the field with a total water capacity of about 60–70%, on which maize had previously been grown. The seedlings were germinated in a thermostat at 10 °C for the first 7 days, and then at 25 °C for 6 days. Subsequently, the seedlings were evaluated using the criteria given for the standard germination test.
The radicle growth (RE) test consisted of sowing eight replicates of 25 kernels each on rolls of tissue paper. The corn kernels were placed on the moistened blotting paper in two rows, with 12 in one and 13 in the other. The blotting papers were then placed in a thermostat at 20 °C. The germinated kernels were identified 66 h ± 15 min after the experiment was set up. Seeds were considered germinated if they had a root length of at least 2 mm [21].
In addition, the vigor index was calculated using the following formula: standard germination (%) × total seedling length (cm). In addition, the average length of the embryonic root of 10 germinated seeds on the blotting paper was determined from each repetition.
2.3. Field Experiments
The field experiments were carried out in a gray-brown podzolic soil (pH = 5.4, measured in 1 M KCl; 1.2% organic matter; 1.07% organic carbon; 144 mg P·kg−1; 138 mg K·kg−1), classified according to the Polish Soil Classification [23], and Albic Luvisols classified according to the IUSS Working Group WRB [24]. The maize was sown in 4 rows, with a row spacing of 0.7 m. The area of each experimental plot was 28 m2 (2.8 m wide × 10 m long), with a harvested area of 14 m2. Mineral fertilizer was applied before sowing at the following rates: 120 kg N·ha−1 in the form of urea, 70 kg P2O5·ha−1 in the form of 20% triple superphosphate, and 130 kg K2O·ha−1 in the form of 60% potassium salt. The sowing of maize in each year of the study was carried out at the end of the third decade of April using a Monosem four-row precision drill (Monosem, Largeasse, France), with a row spacing of 0.7 m, over a length of 10 m. The assumed sowing density was 80,000 seeds ha−1. During the growing season, the herbicide Guardian Complete Mix 664 SE (BASF SE, Ludwigshafen, Germany; terbuthylazine and acetochlor) was used for weed control in 2013 immediately following sowing, at a rate of 3.5 L·ha−1. In subsequent years, Lumax 537.5 SE (terbuthylazine, mesotrione, and s-metolachlor) was applied at a rate of 3.5 L·ha−1. Harvesting was carried out with a plot harvester in the third decade of October.
2.4. Measurements
The leaf area index (LAI), the ratio of leaf area to ground area, was determined using a SunScan Canopy Analysis System of the type SS1 m (Delta-T Devices, Cambridge, UK). Measurements were taken in four replicates at randomly selected locations in the plot during the flowering period (BBCH 61).
The Soil and Plant Analysis Development (SPAD) leaf greenness index was determined twice using the non-invasive SPAD reading method with an N–tester (Yara Company, Oslo, Norway). Measurements were taken at the beginning of shoot elongation (BBCH 30) and during flowering (BBCH 67), with four replicates per plot.
Before harvesting, plant height and the number of cobs per plant were measured for ten randomly selected plants per plot. Then, 10 cobs were randomly taken from each plot, and the number of kernels per cob was determined.
2.5. Weather Conditions
The weather conditions during the maize growth period in the years of the study were evaluated using the hydrothermal index, in accordance with the method of Sielianinov (Table 1). The variability in the weather conditions during the years of the study is reflected using Sielianinov index values. More advantageous moisture conditions for maize plants were found during the year 2013 (K = 1.3) compared to the drier 2014 (K = 1.1) and 2015 (K = 0.8). The formula K = (Mo × 10)/(Dt × days) was applied, where K is the hydrothermal coefficient for an individual month during the growing season, Mo is the total monthly precipitation, and Dt is the mean daily temperature in a particular month.
2.6. Statistical Analysis
The obtained results were statistically analyzed using an analysis of variance (ANOVA) with the SAS package Version 7-1 [25]. Differences in the means of treatment were compared using Tukey’s multiple comparison test. Differences were considered to be statistically significant when the p value was <0.05. To determine the regularities, the correlation coefficients were calculated using Genstat software (VSNi, International, Hempstead, UK). To determine the relationships between seed value and vigor, as well as seed yield and the selected traits of the tested corn varieties for individual seed fractions, the analysis of variance was extended to assess the interdependence among the studied traits. This was performed using Pearson’s linear correlation coefficients, as presented graphically in the form of a heat map.
3. Results
3.1. Seed Value of Kernels
The sowing value of maize cv. ‘Lokata’ seeds depended on the fraction of the seed, with this studied factor significantly affecting parameters such as the germination energy, germination capacity, and share of healthy non-germinating kernels (Table 2). The kernel fraction did not significantly modify the share of abnormally germinating kernels.
The average values of the germination energy and the germination capacity of the ‘Lokata’ seeds during the years of research were high, ranging from 94.7% to 99% and from 95.5% to 99.1%, respectively, depending on the seed fraction. The highest germination energy was observed in large kernels (99%) and medium kernels (97.6%). Large and very large kernels showed similar germination energy values, with no statistically significant differences. Similarly, the germination capacity significantly depended on the seed material fraction. The kernels with the smallest TKW (fraction I) were characterized by a significantly lower germination capacity compared to the kernels of the other fractions. The highest ability was found for very large seeds (99.1%), but no significant difference was found between this seed fraction and the medium (97.9%) and large (98.7%) fractions. The share of abnormally germinating kernels ranged from 0.4 (very large fraction) to 4% in the large seed fraction, but these differences were not statistically confirmed. The highest share of healthy non-sprouting kernels was recorded in the large fraction, and this share was significantly higher than in the remaining fractions. Similarly, the germination capacity values obtained in the Cold test were high, ranging from 85.8% for seeds of the medium fraction to 90.7% for seeds of the large fraction (Table 3).
The seed fraction also significantly modified the values of the conductivity test. Kernels with the highest vigor were found in the large seed fraction (3.33 µS cm g−1), followed by the very large, medium, and small fractions. The highest vigor of the large kernels was further confirmed by the RE, SGT, SGRT, and vigor index. The RE and SGT values varied significantly according to the seed fraction tested. The highest values for these tests were recorded for the large kernels, but there was no significant difference between the small and large kernels fractions. The seedling growth test results indicate that the longest seedlings were recorded for the large kernel fraction. Similar correlations were noted for the dry weight of a single seedling (SGRT) and the vigor index, with seedlings of high vigor obtained from large kernels. The lowest vigor was found in seeds with the highest TKW, as confirmed by the RE, SGT, SGRT, and vigor index tests. Seed vigor was slightly different in the conductivity test, where the lowest vigor was found in seedlings from the small seed fraction. The seed fraction categorized according to the TKW significantly influenced the length of the radicle (Figure 1).
The longest radicle was found in the large seed fraction (11.7 cm), but no significant differentiation of this trait was found between the small and medium, medium and large, or small and large fractions. A significant decrease in the root length was demonstrated in the very large fraction, with a difference of 2.5 cm (21.4%) compared to the large fraction.
3.2. LAI and SPAD
The seed fraction did not significantly affect the values of the leaf greenness index (SPAD), measured at the beginning of stem growth (BBCH 30) and at the flowering stage (BBCH 67), nor the leaf area index (LAI), measured at the flowering stage (Table 4).
The leaf greenness index (SPAD) of maize in the BBCH 30 phase ranged from 487 after sowing large-fraction seeds to 505 after using the medium fraction. In the BBCH 67 phase, the lowest result (766) was recorded when using the small-fraction seeds, and the highest result (796) was recorded after sowing the large fraction seeds. However, these differences were not statistically significant. In addition, the LAI was not influenced by the tested factor.
3.3. Seed Yield and Components
The analysis of variance did not show any significant influence of the seed fraction on the seed yield of maize, cv. ‘Lokata’ (Table 5). The highest yield was observed after sowing the very large fraction (104.4 dt ha−1). The lowest seed yield was recorded after using the small fraction (97.4 dt ha−1). Among the yield components, the seed fraction did not significantly modify the number of cobs per 1 m2. On the other hand, a significant influence of the seed fractions used for sowing was observed on the weight of a thousand kernels and the number of kernels per cob. The number of cobs per 1 m2 did not significantly depend on the fraction of seeds and ranged from 7.7 pcs m2, after sowing the small seeds, to 8.2 pcs m2, after using the medium fraction (Table 5).
The seed fraction used for sowing significantly influenced the weight of TKW. In fact, the lowest TKW was recorded in plants obtained after sowing the small, large, and very large fractions, and a significantly higher TKW was observed after sowing the medium fraction (355.6 g). The lowest number of kernels per cob was recorded for the small fraction (500.9 g).
The analysis of the relationship between the seed yield and selected characteristics of ‘Lokata’ with the small seed fraction showed that the seed yield was most positively correlated with plant height (r = 0.861 ***), the seedling growth test (r = 0.846 ***), the vigor index (r = 0.828 ***), the dry weight of a single seedling (r = 0.727 **), and the number of kernels per cob (r = 0.671 *). It was negatively correlated with the cold test (r = −0.870 ***) and the conductivity test (r = −0.846 ***) (Figure 2).
For the medium seed fraction, the seed yield was positively correlated with the dry weight of a single seedling (r = 0.932 ***), plant height (r = 0.883 ***), the vigor index (r = 0.643 *), the LAI (r = 0.628 *), the seedling growth test (r = 0.595 *), and the number of kernels per cob (r = 0.759 **). It was negatively correlated with the cold test (r = −0.900 ***) and the conductivity test (r = −0.865 ***) (Figure 3).
For the large seed fraction, the seed yield was also positively correlated with the vigor index (r = 0.880 ***), the seedling growth test (r = 0.864 ***), the dry weight of a single seedling (r = 0.833 ***), plant height (r = 0.771 **), and the number of kernels per cob (r = 0.606 *). It was negatively correlated with the cold test (r = −0.810 **) and the conductivity test (r = −0.645 ***) (Figure 4). Additionally, significant correlations of seed yield with germination capacity (r = 0.644 *) and the TKW (0.636 *) were found in this fraction.
For the fraction of very large kernels, a positive relationship of seed yield was noted only with plant height (r = 0.779 **) and the number of kernels per cob (r = 0.809 **). In contrast, a negative relationship with seed yield was found for most of the tested features, i.e., the TKW (r = −0.791 **), the cold test (r = −0.930 ***), the seedling growth test (r = −0.814 **), the conductivity test (r = −0.811 **), the RE test (r = −0.655 *), the seedling growth rate test (r = −0.693 *), and the vigor index (r = −0.696 *) (Figure 5).
4. Discussion
The use of high-quality seeds can increase the yield potential of plants by increasing their resistance to adverse environmental conditions, improving emergence, and promoting favorable subsequent growth and development [26,27,28]. The main measure of seed viability is the germination capacity. This is a basic parameter used for assessing seed quality and is commonly used in agricultural practices to calculate the sowing standard [29,30]. To determine the maximum germination potential of seeds, the germination capacity was assessed in the laboratory under optimal conditions (humidity, temperature, and substrate). If there are favorable environmental conditions in the field, the seed germination capacity is correlated with field emergence. However, well-germinated seeds under controlled conditions in a laboratory do not always respond similarly under field conditions [22].
The genotype can also influence the germination capacity and vigor of seeds [31,32]. Therefore, increasingly, to determine the optimum level of seed activity during storage, germination, and emergence, numerous vigor tests are carried out in seed diagnostics. Seed vigor is a complex trait that encompasses the properties primarily responsible for the physiological potential of seeds, reflected in their rapid and uniform germination, high emergence, and the development of normal seedlings across a wide range of environmental factors [33]. To assess the vigor of seed lots, tests that introduce environmental stress or other conditions (direct tests) or ones that measure selected seed traits related to seedling growth and development (indirect tests) are used. Vigor tests can provide more precise seed quality values than the standard germination test. Moreover, they can provide information on the emergence and storage potential of seed lots. In recent years, especially in the central European region, there has been a lack of optimal field conditions in spring. Higher seed vigor may be crucial for improving level of emergence and uniformity and, subsequently, for plant growth, development, and even yields [26]. The literature indicates that differences in seed germination may also occur after different storage periods [34,35,36,37,38]. In our study, during the three-year period of seed storage under controlled conditions, no deterioration of seed value parameters was recorded in any of the seed fractions tested, so seeds from the same seed lot were used for sowing in all years of the field experiments. Similarly, after the storage of dressed maize seeds, no changes in their germination capacity were observed in the cold test [39].
Seed size is an important physical indicator of seed quality that can significantly influence vegetative growth and, subsequently, seed yield [40]. The seed fraction affects seed quality and crop yield [15]. There is a strong relationship between seed size and nutrient abundance, with larger seeds being beneficial for seedling development [40]. The seed fraction is also correlated with the germination rate. Therefore, the correlation between seed weight and germination is an important factor in determining seed quality [16]. In our study, the highest germination energy and germination capacity were found in kernels of the large fraction. In contrast, significantly lower values for this trait were obtained by sowing small and very large kernels. An earlier study by Panasiewicz et al. [41] showed a significantly lower germination capacity in the largest fraction of maize seeds of the cultivar ‘Boruta’. Lower values of germination energy and germination capacity in studies on maize with seeds of the large and very large fractions, compared to kernels of the small fraction, were also reported by [15,42]. Bieniek et al. [43], in studying three maize varieties with five seed fractions differing in thousand-kernel weight, showed the lowest germination energy and germination capacity values for the smallest fraction. Additionally, higher germination capacities of large maize kernels were obtained by Molatudi and Mariga [44], Yusuf et al. [45], and Gagenau et al. 2023 [46].
The cold test is a vigor test that takes into account unfavorable field conditions, such as soil moisture, the presence of pathogenic fungi in the soil, and low temperature [33]. The vigor tests used in this study showed similar correlations, indicating their potential for broad diagnostics of maize seed quality. From the practical point of view of assessing seed quality for the seed production of this species, the conductivity test appears to be the most justified method for assessing seed vigor, due to the short period of assessment. However, it should be kept in mind that, of the vigor tests, this is the only test where a high value indicates lower seed vigor. The results from all vigor tests indicate that the seed fractionation is an important factor for seed quality. Under stress conditions (cold test) the highest seed quality can be expected from the large fraction. This seed fraction had the highest germination capacity in the RE test and vigor index, as well as the longest seedlings, with the highest dry weight and the lowest conductivity test score. This research indicates a further need to analyze other three-line hybrid varieties, as well as SC and DC varieties. The analysis of kernel germination, assessed using the cold test in our study, showed the highest seed vigor in the large fraction. However, further increases in the sown fraction resulted in a decrease in the value of this trait, but this difference was not statistically significant. Studies by Sulewska and Koziara [47] and Sulewska et al. [15] also indicated that seed size had a significant effect on germination capacity, as assessed using the cold test, with the proportion of germinated kernels decreasing as the weight of a thousand kernels increased. Seed quality is genetically determined but also controlled by environmental factors that influence the growth of maize hybrid varieties [46,48]. The correlation between seed weight and germination was found to be significant for small fractions [16].
The evaluation of maize seed vigor using the root growth (RE) test in this study showed similar relationships to the cold test, with the highest seed vigor found in the large seed fraction. The longest seedlings were found when using the small and large fractions, while the shortest seedlings and the lowest dry weight were shown when sowing the very large fraction. Similar results were observed for the seed vigor index, consistent with the findings of Panasiewicz et al. [41]. In their study, the kernel fraction significantly modified the length of the embryonic root, but the effects were dependent on the cereal plant species [41]. An increase in the fraction of kernels to the large fraction contributed to an increase in the length of the embryonic root, while kernels of the very large fraction produced the shortest embryonic root.
Plant productivity can be significantly affected by photosynthetic processes [49]. The chlorophyll content at the flowering stage of maize (BBCH 67) can be determined based on the assimilation area of a single plant [50]. In our study, the leaf greenness index (SPAD) was measured twice, at the onset of stalk growth (BBCH 30) and at the maize flowering stage (BBCH 67). The obtained results do not indicate a difference in this trait according to the seed fraction. The growth and development of maize are strongly related to the variability in agro-ecological conditions, which can be particularly influential during the initial phases [48].
Seed yield is significantly influenced by genetic conditions [4]. In addition, seed yield can also be significantly determined by environmental conditions [7,13] and agrotechnical conditions [9]. Sulewska and Koziara [47], in an experiment with maize ‘Clarica’, found a decrease in yield when sowing kernels of the medium and large fractions. In a study on maize ‘Boruta’, Sulewska et al. [15] also found a decrease in yield when sowing medium and large versus small seeds, with 13.4 dt ha−1 and 17 dt ha−1, respectively. The highest seed yield in the cultivar ‘Lokata’ was recorded when sowing seeds of the large fraction, and the lowest was found when using the small fraction. The difference was 7 dt ha−1, but this was not statistically significant. The lack of an effect of seed size on maize indicates that this trait is more correlated with conditions during the growing season, the amount of rainfall, and the entire spectrum of environmental conditions [46,51]. Maize seed yield is determined based on the values of individual yield components, which include the number of cobs, the number of kernels per cob, and the TKW. The seed yield also depends on the height of the plants, as well as the length of the cobs [52]. Additionally, the individual yield components are influenced by the earliness of the groups of varieties, as well as their growing region [47]. In our study, the number of cobs was not significantly influenced by the seed fraction.
Seed size is a genetic trait of cultivars [53]. In our study, the TKW was influenced by the seed fraction. The lowest TKW was found when the small fraction was sown, while the highest was found when the medium fraction was used. Similarly, the number of kernels per cob was influenced by the seed fraction; the highest value of this trait was found when the largest fraction was used, while the lowest value was found when the small seed fraction was sown. A similar relationship was also obtained in a study on spring rye and spring wheat by Wasilewski et al. [54]. In our research, the analysis of the obtained results shows the strongest positive correlation between the germination capacity and the seedling growth test, which was particularly evident when using the large seed fraction. Tabakovic et al. [16] observed that the correlation between seed weight and germination was significant for small fractions but did not note a significant correlation between the conducted vigor tests.
In all seed fractions, a significant positive correlation was found between the vigor index and the average seedling length and dry weight of a single seedling. Our results indicate that the seed yield on each of the seed fractions evaluated was significantly correlated with the number of kernels per cob. The study by Ptaszyńska and Sulewska [55] on the maize cultivars ‘Oleńka’, ‘PR39T68’, and ‘Blask’ showed a strong positive correlation between seed yield and the number of kernels per cob, similar to our study. Previous studies [56,57] have indicated that maize grain yield depends on many genetic and non-genetic factors. The literature indicates that high correlations of yield frequently occur with seed weight and kernel number per row in hybrid maize, as reported by [58]. The correlation between seed weight and germination has been found to be significant for small fractions [16,48].
5. Conclusions
Seeds from seed fractions categorized based on the TKW were characterized by different germination rates and vigor levels. Increasing the TKW of the seeds resulted in an increase in the germination and vigor for fraction III (large kernels). Among the vigor tests performed, the strongest positive relationship was found between the germination capacity and the seedling growth test, particularly in the large seed fraction. Sowing seeds with a higher TKW resulted in plants with higher fresh and dry weights in the early stages of maize development. However, this response diminished as growth progressed. The seed fraction significantly influenced plant height. There was no significant effect of seed fraction on the leaf area index or leaf greenness index. Seed yield was found to be significantly correlated with plant height and the number of kernels per cob for all fractions sown. The seed fraction did not significantly influence the seed yield of maize ‘Lokata’.
Conceptualization, K.P. and R.S.; methodology, K.P., J.B. and R.S.; software, K.P., K.R. and J.B.; validation, K.P., R.S., A.F., K.R. and G.S.; formal analysis, K.P. and R.S.; investigation, R.S., G.S. and A.F.; resources, G.S., R.S., A.K. and R.P.; data curation, K.P., R.P. and A.K.; writing—original draft preparation, K.P., R.P. and A.K.; writing—review and editing, K.P., R.P. and A.K.; visualization, K.P., J.B., R.S. and K.R.; supervision, K.P., K.R. and G.S.; project administration, K.P. and A.F.; funding acquisition, K.P. All authors have read and agreed to the published version of the manuscript.
Not applicable.
The data presented in this study are available upon request from the corresponding author.
The authors declare no conflicts of interest.
Footnotes
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Figure 1 Length of the radicle depending on the seed fraction of maize [cm]. Differences between results are indicated by lower case letters, significance level was defined as according to Tukey’s test, at a 5% probability.
Figure 2 Heatmap of correlation coefficients for selected features of small fraction of maize of ‘Lokata’ seeds.
Figure 3 Heatmap of correlation coefficients for selected features of medium fraction of maize ‘Lokata’ seeds.
Figure 4 Heatmap of correlation coefficients for selected features of large fraction of maize ‘Lokata’ seeds.
Figure 5 Heatmap of correlation coefficients for selected features of very large fraction of maize ‘Lokata’ seeds.
Sielianinov hydrothermal index (K) values in the years 2013–2015.
| Year | Months | Average | |||||
|---|---|---|---|---|---|---|---|
| IV | V | VI | VII | VIII | IX | ||
| 2013 | 0.4 | 2.2 | 2.2 | 0.8 | 0.5 | 1.9 | 1.3 |
| 2014 | 1.5 | 1.8 | 0.6 | 0.7 | 1.0 | 0.8 | 1.1 |
| 2015 | 0.6 | 0.6 | 1.3 | 1.4 | 0.5 | 0.6 | 0.8 |
| 1958–2012 | 1.2 | 1.4 | 1.1 | 1.4 | 1.1 | 1.0 | - |
The K values are categorized as follows: <0.5 = drought; 0.5–1.0 = semi-drought; 1.0–1.5 = border of optimal moisture; and >1.5 = excessive moisture.
Seed values of maize ‘Lokata’ seeds depending on seed fraction.
| Seed Fraction | Germination Energy | Germination Capacity | Share of Abnormally Germinating Kernels [%] | Share of Healthy Non-Germinating Kernels [%] |
|---|---|---|---|---|
| I—small (244 g) | 94.7 c * | 95.5 b | 2.9 a | 1.6 a |
| II—medium (296 g) | 97.6 b | 97.9 a | 1.5 a | 0.6 b |
| III—large (334 g) | 99.0 a | 98.7 a | 1.0 a | 0.3 b |
| IV—very large (396 g) | 94.8 c | 97.3 a | 0.4 a | 0.5 b |
* Means followed by the same letter in the columns do not differ significantly according to Tukey’s test, at a 5% probability.
Seed vigor of maize cv. ‘Lokata’ depending on seed fraction.
| Seed Fraction | Cold Test | Radicle Growth (RE) [%] | Seedling Growth Test [cm] | Seedling Growth Rate Test [mg] | Conductivity Test | Vigor Index |
|---|---|---|---|---|---|---|
| I—small (244 g) | 86.1 ab * | 88.3 c | 4.30 bc | 14.1 ab | 4.84 d | 411 b |
| II—medium (296 g) | 85.8 a | 82.0 b | 4.13 b | 16.0 b | 4.00 c | 405 b |
| III—large (334 g) | 90.7 b | 90.9 c | 4.64 c | 17.7 c | 3.33 a | 457 c |
| IV—very large (396 g) | 88.4 ab | 72.7 a | 3.23 a | 13.2 a | 3.51 b | 308 a |
* Means followed by the same letter in the columns do not differ significantly according to Tukey’s test, at a 5% probability.
SPAD and LAI depending on the seed fraction of maize.
| Seed Fraction | SPAD [BBCH 30] | SPAD [BBCH 67] | LAI |
|---|---|---|---|
| I—small (244 g) | 491 a * | 766 a | 3.4 a |
| II—medium (296 g) | 505 a | 772 a | 3.5 a |
| III—large (334 g) | 487 a | 796 a | 3.3 a |
| IV—very large (396 g) | 489 a | 781 a | 3.5 a |
* Means followed by the same letter in the columns do not differ significantly according to Tukey’s test, at a 5% probability.
Yield components and seed yield depending on the seed fraction of maize.
| Seed Fraction | Number of Cobs | TKW | Number of Kernels in Cob [pcs.] | Seed Yield |
|---|---|---|---|---|
| I—small (244 g) | 7.7 a * | 343.9 b | 500.9 b | 97.4 a |
| II—medium (296 g) | 8.2 a | 355.6 a | 533.7 a | 100.8 a |
| III—large (334 g) | 7.8 a | 345.4 b | 518.9 b | 106 a |
| IV—very large (396 g) | 7.9 a | 346.1 ab | 540.8 a | 104.4 a |
* Means followed by the same letter in the columns do not differ significantly according to Tukey’s test, at a 5% probability.
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; Sobieszczański Rafał 1 ; Ratajczak Karolina 1
; Faligowska Agnieszka 1
; Szymańska Grażyna 1
; Bocianowski, Jan 2
; Kolanoś Anna 1 ; Pretkowski Rafał 1 1 Department of Agronomy, Faculty of Agronomy, Horticulture and Biotechnology, Poznań University of Life Sciences, Dojazd 11 Str., 60-632 Poznań, Poland; [email protected] (R.S.); [email protected] (K.R.); [email protected] (A.F.); [email protected] (G.S.); [email protected] (A.K.); [email protected] (R.P.)
2 Department of Mathematical and Statistical Methods, Poznań University of Life Sciences, 60-637 Poznań, Poland; [email protected]