The Impact of Weather Conditions and Storage Duration on the Germination of Croatian Winter Wheat (Triticum aestivum L.) Varieties

Abstract

Seed germination is a key determinant of wheat seed quality, strongly affected by genetic potential, weather conditions during production, and storage duration. Although numerous studies have investigated seed viability, little is known about how the interaction between annual climatic variability and storage length affects long-term germination performance of winter wheat. The objective of this study was therefore to assess the influence of weather conditions and storage period on germination energy and germination of 50 Croatian winter wheat (Triticum aestivum L.) cultivars released between 1947 and 2010. The experiment was conducted over five consecutive production years (2013/2014–2017/2018). Seeds of each cultivar were reproduced under standardized field conditions, harvested annually, and stored under identical controlled conditions (5 °C, 30–35% RH). Germination energy (first count, day 4) and total germination (final count, day 8) were evaluated according to ISTA protocols. The results revealed significant effects of both production year and cultivar on germination performance. Seeds produced in 2016/2017 exhibited the highest germination (96.21%), which was ~15% higher than the lowest rate observed in 2013/2014 (80.48%). Germination energy of 2013/2014 seeds was 23% lower compared to 2015/2016 and 2016/2017. Unexpectedly, seeds stored for only one year (2017/2018 production) showed lower germination (90.92%) than those stored for two (96.21%) or three years (95.01%), likely due to excessive rainfall (>100% above average) during seed maturation in 2018 that impaired seed quality. Several cultivars, including Una, Tonka, Žitarka, and Kuna, consistently maintained high germination rates (>94%) even after five years of storage, demonstrating strong physiological stability and long-term viability. These findings underline the combined importance of weather conditions during seed production and storage duration for seed longevity. In practical terms, cultivars with proven stability may be recommended for long-term storage and reliable field performance. Future research should extend germination assessment to additional vigor indices (e.g., germination synchrony, vigor index, abnormal seedlings) and explore genetic mechanisms underlying superior seed longevity in modern wheat breeding.

1. Introduction

Wheat is one of the most important agricultural crops for human consumption and is used in the milling, food and pharmaceutical industries. The largest wheat producers in the world are China, the United States, India, Russia, Canada and France, while the highest grain yields are achieved in the less developed European countries. Today, 14 types of wheat are grown worldwide, but the most common are: Triticum aestivum (87%), Triticum compactum (3%) and Triticum durum (10%) [1].

Seed germination is the most important component of seed quality and depends primarily on the genetic potential of varieties [2]. According to the ISTA ([3]), the process of seed germination comprises four sub-phases: water uptake, activation of enzymatic systems, initiation of growth and seedling. Some environmental factors such as temperature, soil moisture, salinity and light simultaneously influence seed germination [4]. High quality seed is essential for wheat productivity. The seed must have a high percentage of germination, a tested seed weight and purity. The lack of any of these three factors is likely to result in low quality and low grain yield [5]. Seed longevity is a complex trait regulated by diverse genetic pathways, notably those associated with antioxidant defense, DNA repair, and hormonal signaling [6]. Seed longevity depends on the interaction between genetic and environmental factors, with ABA as the main positive regulator; GAs and BRs also contribute through their role in seed coat development, potentially influencing seed viability [7]. Another important factor is the method of seed storage after harvest. Improper seed storage leads to up to 10% lower germination capacity and thus poorer seed quality [8]. The cold chambers in which the seeds are stored should preserve the longevity of the seeds due to the controlled conditions compared to seeds stored outside cold chambers without controlled conditions [9]. A study investigated [10] the germination of seeds considering the duration of storage. The author found that weather conditions are the most important factor influencing seed germination before storage.

The aim of this study was to evaluate the differences in germination energy and total germination among 50 winter wheat cultivars, taking into account the duration of storage and the weather conditions during each seed production year. The selection of cultivars spanning the period from 1947 to 2010 was intentional to represent different wheat breeding eras in Croatia. This range captures decades of breeding progress and encompasses a broad genetic base, reflecting diversity in agronomic performance, adaptation, and seed longevity potential.

2. Materials and Methods

The research was conducted on 50 winter wheat (Triticum aestivum L.) cultivars developed by five Croatian breeding centers and officially recognized between 1947 and 2010. Over a five-year period, these cultivars were annually reproduced under standardized field conditions at different experimental sites. Each year, newly harvested seed from each cultivar was collected, and stored in controlled climate chambers under uniform post-harvest conditions. All seed samples were stored under identical conditions in a controlled climate chamber at 5 °C and approximately 30–35% relative air humidity. Seeds were placed in hermetically sealed aluminium foil bags and maintained at a seed moisture content of approximately 10%, as determined prior to storage. These conditions were selected to preserve seed viability and minimize environmental variation across storage years. This approach ensured genetic consistency through cultivar identity while allowing weather variation between years to influence seed development. Seed germination from all five production years was evaluated in 2019, encompassing seed lots with varying storage durations, ranging from one storage year(production year 2013/2014) to five storage years (production year 2017/2018). This experimental design enabled the evaluation of both cultivar stability and the interaction of annual weather conditions and storage duration on seed germination and viability.

2.1. Field Experiment

The trial was planted on a plots measuring 5 m × 1.25 m (6.25 m) each. It was carried out in five growing seasons (2013/2014–2017/2018). Due to crop rotation, the experiment was sown on two soil types: loamy soil and eutric brown soil. Fertilization was carried out annually based on the results of agrochemical soil analysis. The first four years of the experiment were carried out as part of the HRZZ project (Croatian Science Foundation) „PHENOWHEAT” and the following fifth year was implemented as a separate project.

2.2. Climate Data

Data on average monthly air temperatures and total monthly precipitation were obtained from the Croatian Meteorological and Hydrological Service from the measuring station Osijek—Klisa, Croatia (Figure 1).

In the first year of field experiment (2013/2014), the average monthly air temperatures from October to April were higher than the multi-year average (Graph 1). In 2014, June was the warmest month and the lowest temperature was recorded in February. The amounts of precipitation recorded in September 2013 and May 2014 were significantly higher than the average.

In the second year of field experiment (2014/2015), the average monthly temperatures rose slightly compared to the multi-year average. A slightly higher amount of precipitation was recorded in October 2014. In January, February and May, higher levels of precipitation were recorded compared to the multi-year average. Compared to the average, significantly lower amounts of precipitation were measured in April, June and July 2015.

In the third year of field experiment, the average monthly air temperatures were around the multi-year average, except in February 2016, when the temperature was above average. It can be seen that there was more precipitation in February, June and July 2016 and in October 2015.

In the fourth year of field experiment, the average monthly air temperature in February, March and June 2017 was slightly higher than the multi-year average. In December 2016 and in January and June 2017, the air temperatures were lower than the multi-year average.

In the fifth year of field experiment, the average monthly air temperature was higher than the multi-year average, especially in January, April and May 2018. In April and May, a lower amount of precipitation was recorded, and in July of the same year, the total amount of precipitation was significantly higher than the multi-year average.

2.3. Laboratory Experiment

Seed germination and germination energy were tested for each variety according to the ISTA regulations (2017) in three replicates.

Table 1. Wheat seed production years in relation to duration of storage.

Production Year	2017/2018	2016/2017	2015/2016	2014/2015	2013/2014
Duration of storage	one year	two years	three years	four years	five years

shows the production years of seed samples used in the germination study, along with their corresponding storage durations. The seeds were produced over five consecutive vegetation seasons, allowing for the assessment of germination across a range of storage periods from one to five years.

Folded filter paper (21/N 80 g/sqm 580 × 580) is used as medium for the seed germination test. The paper was soaked with the prescribed amount of tap water (66 mL, pH 7.5). Fifty seeds per replicate were spread on the paper with tweezers in 4 rows for each variety. The filter paper was rolled up and placed in labeled PVC bags with the following information: variety name, sowing number, number of replicate. The samples were stored upright in the climate chamber, making sure that the closed end of the roll is pointing downwards so that the seeds could not fall out. The climate chamber was set to constant temperature of 20 °C with a light regime of 12 h day and 12 h night. Four days after placing the samples in the climate chamber, the first count (germination energy) was carried out. The second count was carried out after eight days in order to determine germination.

2.4. Statistical Analysis

The measures of descriptive statistics are included: arithmetic mean (AM), standard deviation (SD) and coefficient of variation (CV%). The differences between the tested varieties for all tested traits were analysed using a one-factorial analysis of variance at a significance level of 99%, followed by Tukey’s HSD test (α = 0.01) to determine statistically significant differences between individual means.”

3. Results and Discussion

3.1. Differences Between Production Years/Storage Duration in Germination Energy

The highest germination energy was noted in seeds harvested in 2016/2017 and 2015/2016 (Figure 2). Germination energy of seeds from 2013/2014 was 23% lower and statistically significantly different from those harvested in the 2016/2017 and 2015/2016 years. Seeds from 2017/2018 and 2014/2015 production year had similar germination energy but statistically significantly different than seeds from 2017/2018 year, and also statistically significantly different than 2016/2017 and 2015/2016 year.

3.2. Differences Between Production Years/Storage Duration in Seed Germination

The differences in seed germination between production years are shown in Figure 3. The highest germination was recorded for the 2016/2017 seeds, which was approximately 15% higher than the lowest germination observed in the 2013/2014 year. Statistically significant differences were found between the 2016/2017 and 2013/2014 years, as well as between the better-performing (2016/2017) and lower-performing (2017/2018, 2014/2015 and 2013/2014) years. The largest difference was observed between the 2016/2017 and 2013/2014.

Table 2. Obtained F value and p value from one-way analysis for the effect of genotype on germination energy and germination in each year of examination.

Production Year	Trait	F-Value	df1	df2	p-Value
2017/2018	Germination energy	6.64	49	100	<0.0001
	Germination	9.15	49	100	<0.0001
2016/2017	Germination energy	4.50	49	100	<0.0001
	Germination	4.77	49	100	<0.0001
2015/2016	Germination energy	5.91	49	100	<0.0001
	Germination	8.45	49	100	<0.0001
2014/2015	Germination energy	7.11	49	100	<0.0001
	Germination	7.73	49	100	<0.0001
2013/2014	Germination energy	10.88	49	100	<0.0001
	Germination	12.10	49	100	<0.0001

Table 2. Obtained F value and p value from one-way analysis for the effect of genotype on germination energy and germination in each year of examination.

Production Year	Trait	F-Value	df1	df2	p-Value
2017/2018	Germination energy	6.64	49	100	<0.0001
	Germination	9.15	49	100	<0.0001
2016/2017	Germination energy	4.50	49	100	<0.0001
	Germination	4.77	49	100	<0.0001
2015/2016	Germination energy	5.91	49	100	<0.0001
	Germination	8.45	49	100	<0.0001
2014/2015	Germination energy	7.11	49	100	<0.0001
	Germination	7.73	49	100	<0.0001
2013/2014	Germination energy	10.88	49	100	<0.0001
	Germination	12.10	49	100	<0.0001

3.3. Differences Between Production Years/Storage Duration in Germination for Each Cultivar

In terms of seed germination after one year of storage, using seed produced in the most recent production season (2017/2018), Felix achieved 100% germination, while the Sana variety (48.00%) has the lowest number of germinated seeds. The average germination rate of all cultivars for the trait of germination is 90.92%. Only three cultivars have a germination rate of less than 80.00%, while 13 cultivars are in the range of 80.01–90.00%. The remaining cultivars are in the range above 90.01% germinated seeds, consisting of 34 cultivars.

In the case of seeds produced during the 2016/2017 vegetation season and stored for two years, three cultivars—Donna, Katarina, and Snaša—achieved a germination rate of 100%.The lowest number of germinated seeds was found in the cultivar Kalista (40.67%), whose germination rate remained unchanged compared to the previously examined germination energy. The average for the total germination for all cultivars is 96.21%. Only 4 cultivars have a germination rate lower than 96%, namely Kalista, Sana, Talia, and Mura. The remaining 46 cultivars have a germination rate in the range of 96–100%.

For seeds produced in the 2015/2016 vegetation season and stored for three years, germination in several cultivars (BC Elvira, BC Patria, Marta, and Matea) was successfully recorded during the first seed count. The average did not differ significantly from the trait of germination energy and amounts to 95.01%. Similarly, the same percentage of cultivars is below and above the average as in the examination of the previous trait. However, 17 cultivars record germination rates from 98 to 100%. It was found that only 4 cultivars (Kuna, Fiesta, Gabi, Bela) are in the range below 90.00%, while 46 cultivars have a recorded germination rate higher than 90.01%.

For seeds produced during the 2014/2015 vegetation season and stored for four years, the highest germination rate was recorded in the cultivar Bela (100%),followed by Mihelca (98.67%), Bianca (98.00%), Marija (98.00%), Nova Žitarka (98.00%), Tonka (98.00%), and Una (98.00%). The lowest germination rate was found in the cultivar Prima (58.00%), while slightly higher percentage (66.00%) is contained in BC Patria. The average for all cultivars for the examined trait is 91.57%. As in the examination of germination energy, 36% of cultivars are below average, while 64% are above average. Only two cultivars have a determined germination rate of less than 70.00%, and 14 cultivars have a determined range of germinated seeds from 80.01 to 90.00%. The rest of the cultivars make up the majority and contain more than 90.01% of germination.

For seeds produced in the 2013/2014 vegetation season and stored for five years, the highest germination rate was observed in the cultivar Una (95.33%),while the lowest percentage is recorded by the cultivar Sana (34.67%), which constitutes a statistically significant difference. The average for all cultivars for the germination trait is 80.48%. Cultivars below average constitute 17 cultivars, and 33 cultivars are above average. For the examined trait, cultivars are divided into five different ranges. The first range consists of only 3 cultivars with a germination rate lower than 60.00%. In the range of 60.01–70.00%, there are 7 cultivars, and 7 cultivars make up the range of 70.01–80.00%. The largest percentage of germination is represented by 23 cultivars in the range of 80.01–90.00%. In the range above 90%, there are 10 cultivars.

Based on the Tukey HSD test, differences between individual genotypes were determined for the investigated trait (

Table 3. Germination (%) for each production year.

Cultivar	2017/2018	2016/2017	2015/2016	2014/2015	2013/2014	Mean ± SD
Storage Duration (years)	1	2	3	4	5
SANA	48.00	74.00	99.33	89.33	34.67	69.07 ± 27.28
KALISTA	92.00	40.67	96.00	93.33	84.00	81.20 ± 23.09
TALIA	90.67	94.00	92.67	82.67	51.33	82.27 ± 17.84
BC PATRIA	89.33	96.67	100.00	66.00	65.33	83.47 ± 16.70
TENA	81.33	96.67	94.67	83.33	72.67	85.73 ± 9.94
PRIMA	92.67	98.67	98.67	58.00	81.33	85.87 ± 17.11
MARTA	92.00	96.67	100.00	90.67	56.00	87.07 ± 17.76
ADRIANA	86.00	98.00	96.00	96.67	61.33	87.60 ± 15.44
SRPANJKA	82.00	96.00	93.33	86.00	80.67	87.60 ± 6.81
KATARINA	80.00	100.00	99.33	87.33	72.67	87.87 ± 11.96
ALKA	84.67	97.33	98.00	94.67	66.67	88.27 ± 13.20
FIESTA	90.00	98.67	82.67	86.00	84.67	88.40 ± 6.34
KOLEDA	74.67	99.33	96.67	93.33	79.33	88.67 ± 10.98
BC ELVIRA	88.67	98.67	100.00	93.33	63.33	88.80 ± 14.93
KATA	88.67	96.67	98.00	96.00	65.33	88.93 ± 13.69
ANA	95.33	96.67	99.33	85.33	69.33	89.20 ± 12.31
PANONIJA	93.33	96.00	99.33	96.00	63.33	89.60 ± 14.84
KUNA	94.67	98.67	76.00	85.33	94.00	89.73 ± 9.09
DIVANA	98.00	99.33	98.00	82.67	71.33	89.87 ± 12.42
BELA	84.67	97.33	87.33	100.00	84.00	90.67 ± 7.47
ZLATNA DOLINA	94.67	98.67	90.67	88.67	81.33	90.80 ± 6.54
ILIRIJA	90.00	97.33	90.67	87.33	90.00	91.07 ± 3.73
GABI	93.33	97.33	84.67	94.00	86.67	91.20 ± 5.32
SEKA	88.00	96.67	98.00	95.33	79.33	91.47 ± 7.81
NEVENA	95.33	98.67	95.33	92.00	76.67	91.60 ± 8.67
RENATA	91.33	98.00	92.00	89.33	89.33	92.00 ± 3.56
JASNA	96.67	96.67	99.33	96.00	73.33	92.40 ± 10.74
AFZG KAJA	93.33	97.33	96.00	95.33	82.67	92.93 ± 5.92
KRUNA	96.67	99.33	91.33	96.00	82.67	93.20 ± 6.55
ŽITARKA	89.33	97.33	96.00	89.33	94.00	93.20 ± 3.72
HELIA	90.00	98.67	91.33	97.33	89.33	93.33 ± 4.35
MURA	96.67	94.67	90.67	95.33	89.33	93.33 ± 3.16
MATEA	90.67	96.00	100.00	95.33	85.33	93.47 ± 5.63
LUCIJA	90.67	99.33	92.67	92.67	92.67	93.60 ± 3.32
PIPI	92.67	99.33	93.33	90.00	92.67	93.60 ± 3.45
NOVA ŽITARKA	94.67	98.67	97.33	98.00	80.67	93.87 ± 7.53
BANICA	92.00	96.67	96.67	94.00	91.33	94.13 ± 2.51
MARIJA	90.00	98.67	99.33	98.00	84.67	94.13 ± 6.50
SNAŠA	92.67	100.00	98.00	96.00	84.67	94.27 ± 6.01
MIA	96.67	98.67	96.00	93.33	87.33	94.40 ± 4.39
DEA	95.33	98.67	94.67	94.00	90.00	94.53 ± 3.11
CERERA	99.33	98.67	92.67	91.33	91.33	94.67 ± 4.00
EMA	94.67	97.33	98.00	96.00	88.00	94.80 ± 4.01
BIANCA	93.33	99.33	96.00	98.00	88.00	94.93 ± 4.49
MIHELCA	92.67	97.33	96.00	98.67	90.00	94.93 ± 3.55
AFZG KARLA	94.67	98.00	95.33	97.33	90.00	95.07 ± 3.15
DONNA	99.33	100.00	92.67	94.00	90.67	95.33 ± 4.13
FELIX	100.00	96.67	96.67	94.00	90.67	95.60 ± 3.48
TONKA	96.00	97.33	97.33	98.00	94.67	96.67 ± 1.33
UNA	98.67	99.33	96.67	98.00	95.33	97.60 ± 1.61
Tukey HSD	8.68 **	13.13 **	5.33 **	8.95 **	11.95 **
CV (%)	8.87	9.14	5.00	8.34	15.86

** Statistically significant at the p < 0.01 level.

).

The coefficient of variation (CV%) provides a standardized measure of dispersion, where values below 10% indicate low variability, 10–15% moderate variability, and above 15% high variability in seed germination among cultivars within each year. Lower CV values (5.00% in the 2015/2016) indicate more uniform germination among cultivars, whereas higher values (15.86% in the 2013/2014) reflect greater inconsistency and differentiation between cultivars. This progression illustrates how storage time amplifies differences in seed viability among wheat cultivars.

4. Discussion

Since the seeds originated from different production years, the observed differences in germination were influenced by both the environmental conditions prevailing during each growing season and the varying storage durations, as both factors play a critical role in seed viability and physiological quality.

The analysis of seed germination energy and total germination during different storage periods shows a consistent trend of decreasing values with increasing storage time. In particular, seeds stored for five years showed significantly lower germination rates than those stored for shorter periods. These results are consistent with previous studies [11], which reported a 38% decrease in germination after five years of storage under sealed storage. Of the crops tested, wheat maintained the highest germination rates, while maize had the lowest. This underlines the importance of crop-specific factors for seed viability over time [11].

In addition to precipitation patterns, temperature and humidity are widely recognized as key factors affecting seed viability during storage. Germination refers to the first visible signs of growth, a process highly sensitive to both biotic and abiotic stresses [12]. Several studies [13,14,15,16] emphasize that elevated temperatures and increased seed moisture content during storage significantly reduce seed longevity. [14] Previous research demonstrated that reducing seed moisture extends storage duration [14], while other studies confirmed that high temperature combined with high humidity has the most detrimental effect on seed preservation [15,16]. The differences in seed germination between production years can be directly linked to the climatic conditions shown in the climate diagram. Years with favourable temperatures and well-distributed precipitation, such as 2014/2015 and 2015/2016, resulted in higher average germination rates due to optimal grain filling and seed maturation. In contrast, years with excessive rainfall during harvest or temperature extremes, like 2013/2014 and 2017/2018, led to greater variability and lower germination in sensitive cultivars. These findings confirm that weather conditions during the growing season significantly influence seed viability in storage, supporting similar conclusions in previous studies. The lower germination of seeds produced in the 2013/2014 season may also be attributed to seed age.

Notably, germination energy (88.45%) and germination (90.92%) were lower in seeds stored for one year than in those stored for two or three years. This counterintuitive pattern is likely a consequence of the exceptionally high rainfall recorded during the 2017/2018 growing season, particularly in the seed maturation period, which adversely affected seed physiological quality. In July 2018, precipitation (115.6 mm) exceeded the multi-year average (57.4 mm) by more than twofold, with similarly elevated values in June (103.2 mm). Excessive rainfall during seed development can impair seed viability by disrupting maturation processes and increasing susceptibility to pathogens, thereby explaining the reduced germination observed after only one year of storage [10,17].Consistent with these findings, it was concluded that prolonged storage, especially when combined with high seed moisture content, has negative effects on germination [18].importance of pre-storage weather conditions and storage environment itself in maintaining seed germination, reporting a two-year range between 63% and 82%, with optimal storage periods for winter wheat between six and eighteen months [10]. Similarly, a steady decline from 94.7% to 69.8% over an eighteen-month storage period [19].

Long-term investigations by highlighted variability in seed viability across cultivars stored for up to thirty years [20]. This variability supports the findings of the present study, where specific cultivars demonstrated superior germination stability. For example, the oldest cultivar tested, Banica, retained ≥90% germination after five years of storage. Other high-performing cultivars, such as Una, Tonka, Žitarka, and Kuna, also exhibited high germination rates, indicating robust physiological stability and a favorable genetic profile. In addition to high germination percentages, these cultivars showed low interannual variability, indicating strong physiological stability. These results also highlight the importance of evaluating the stability of the genotype or the studied trait, which is essential for facilitating the breeding process.

Several studies [21,22,23] have emphasized that the optimal temperature for wheat seed germination is between 20 °C and 30 °C. Reference [24] also confirmed that both germination energy and germination decrease with increasing seed age, corroborating the observations of this study.

In summary, the results of this study reinforce existing knowledge on the detrimental effects of prolonged storage on seed germination and emphasize the crucial role of both storage conditions and cultivar-specific genetic traits in maintaining seed viability. Moreover, the variability in germination observed among seeds from different production years highlights the significant influence of weather conditions during seed development, which can affect initial seed quality and its subsequent ability to withstand storage. Future studies should focus on identifying the genetic mechanisms that contribute to seed longevity, particularly in modern wheat cultivars, in order to improve conservation strategies and enhance agricultural productivity. Also, additional analyses such as expanded germination metrics, germination synchrony, and seedling vigor metrics could be applied in future research, as they would provide a more comprehensive understanding of seed vigor dynamics. Their inclusion would greatly contribute to the novelty and practical value of such studies.

5. Conclusions

Based on the conducted research, statistically significant differences were observed between tested wheat cultivars and between different production years with regard to germination energy and total germination. The results confirmed that both genetic background and annual weather conditions during seed production influenced seed longevity under controlled storage conditions. From a practical agricultural standpoint, the findings of this study support the recommendation of certain winter wheat cultivars for sowing in Croatia. Cultivars such as Una, Tonka, Žitarka, and Kuna consistently demonstrated excellent germination parameters (>94%) even after five years of storage. Their strong physiological stability and high germination rates suggest they are well-suited for long-term storage and reliable field emergence, making them valuable choices for Croatian wheat production systems.