Effects of seed packaging,storage conditions,and durations on seed quality of open-pollinated maize ( Zea mays L.) varieties in Ethiopia

Abstract

Objective

This study investigates the combined effects of storage environments and packaging materials on the seed quality of open-pollinated maize (Zea mays L.) (OPM) varieties intended for planting purposes after long-term storage.

Methods

Melkassa-2, Melkassa-4, and Melkassa-6Q seeds were stored under cold and ambient storage conditions. Subsequently, the seeds were packed into Polypropylene woven bags and multilayer polyethylene lined hermetic (Super GrainPro (SGPr) and Purdue Improved Crop Storage (PICS)) bags and stored for 24 months. The combined analysis was done using a completely randomized design (CRD) with factorial arrangement replicated three times. The temperature of the refrigerator for cold storage was maintained at 5 ±3 °C with a relative humidity of 42 ±3%. In 2021, the annual mean temperature of ambient conditions ranged from 14.27 to 28.57 °C with relative humidity (RH) between 47% and 75%. In 2022, the annual mean temperature ranged from 13.97 to 29.51 °C with RH between 40.10% and 70.13%. The evaluation was conducted at Melkassa Agricultural Research Center. Seed quality traits were measured every 6 months for 24 months.

Results

The study found significant interaction (P≤0.05) effects between storage environment, maize variety, and seed packaging material on seed germination after 18 and 24 months of storage. Hermetic bags under cold storage maintained seed quality for up to 24 months, while non-hermetic bag under ambient storage preserved seeds for up to 12 months. Non-hermetic storage bags led to a decline in seed quality after 12 months.

Conclusions

Hermetic bags (PICS) combined with cold storage can prolong the shelf life of EGS for open-pollinated maize varieties for up to 24 months. However, SGPr and PPW bags stored under the same conditions showed significant deterioration after 12 months. This approach can help improve seed quality and longevity, leading to accessibility for breeding programs, EGS producers, and smallholder farmers.

Keywords

physiological quality seeds quality open-pollinated maize hermetic bags non-hermetic bags storage conditions storage longevity

1. Introduction

Maize (Zea mays L.) is the most important staple food crop and ranks second in terms of area coverage after tef (Eragrostis tef (Zucc.) Trotter) in Ethiopia.¹ Maize is a crucial crop in Ethiopia, primarily grown in the meher season. It can be used as a source of fructose, corn oil, and starch, with a wide range of applications.² Despite its economic and food security value, inadequate storage leads to significant postharvest losses for producers in developing countries.³ In 2018/2019, maize production reached 9.49 million tons, cultivated by 9.86 million farmers on 2.37 million hectares of land.¹ Less than 5% of the cultivated areas are covered by improved open-pollinated crop seeds.⁴ The majority of the area is covered by informal seeds, while some are by formal and intermediate seeds. The informal seed can be supplied through seed exchange mechanisms from farmer-to-farmer and from traders to farmers by buying. This seed supply system has been contributing about 80 to 90% but characterized by poor quality seeds. In the formal and intermediate seed supply system, both public and private producers contribute only 10-20% of the actual demand of the country.⁴ Accessibility of open-pollinated crop seeds can be improved because once obtained, improved seeds are usually recycled by farmers for about three to four years without affecting varietal purity, unlike hybrid seeds.⁵ In addition to genetic variability, poor post harvest management practices such as storage conditions, storage structures, and storage longevity contribute to significant losses in seed quantity and quality. Inadequate agronomic practices and low seed productivity can result mainly from the use of poor quality seeds for planting.

Optimal storage conditions are a fundamental to improve the efficiency and maintain the quality of formal and intermediate seed systems. Seeds with high viability and vigour establish well in the field condition.⁶ The primary environmental factors responsible for seed quality deterioration include temperature, relative humidity, type of storage containers, storage periods and moisture content of the seeds. The hygroscopic nature of maize seeds some times makes them unsuitable for storage in open containers.⁷ High temperatures above 25 °C and a relative humidity of 65-70% can reduce seed viability and vigour if stored for more than 3-4 months. To prevent this, ensure proper container and moisture levels.⁸ A quantitative loss of 10-20% of maize occurs during storage due to poor storage systems, resulting in the decline of seed viability and vigour.⁹ In the Central Rift Valley region of Ethiopia, on-farm storage conditions for recycled seeds are not ideal for maize seed longevity.⁵ This is because the ambient temperatures can exceed 33°C, and the relative humidity levels can reach up to 75%.¹⁰ The rate of seed deterioration varies among crop types, storage environments and packaging types. Starchy seeds, such as cereals, generally deteriorate at a slower rate compared to oily legume seeds with high protein content, when all other factors such as temperature, relative humidity and moisture content are the same.¹¹

Seed physiognomies must be maintained after harvest to ensure high quality for customers.¹² Physiological properties of seed quality must be preserved during storage to meet consumer demands.¹² During storage, fluctuations of seed moisture content that exceed national standards, along with other factors, can impact physical and physiological quality of stored seeds. Ambient and cold storage conditions, packaging types and crop varieties are major factors affecting seeds quality during storage. Different storage strategies depend on the initial drying of the seeds. Storing seeds with high moisture content may lead to increased damage to the stored seeds even if they are stored in hermetic bags.¹³ A decline in seed quality due to poor storage conditions leads to extremely low-quality seed that is unacceptable for planting.¹⁴ Low-quality seed leads to lower plant stands establishment and a corresponding loss in yield.¹⁵ Seed should be stored in facilities that can maintain sound seed germination and vigour.¹⁶ The storage conditions significantly influence the sustainability of seed viability. Consequently, minimizing qualitative seed loss can improve crop productivity.¹⁷

The seed packaging materials are strongly influence seed quality.¹⁸ A hermetic bags are cost-effective and safe method for storage, preventing insect infestations and preserving the quality of grains for short and long-term preservation without refrigeration.¹⁹ Polypropylene woven bags are quite cheap but more porous than moisture proof hermetic and PICS bags. Polypropylene bags are moisture pervious, very economical and reusable, and can be used for seed storage. Improved hermetic containers, such as metal silos, PICS, and Super GrainPro bags are offering an interesting alternative to traditional storage materials. The hermetic bags work on the principle that seeds release carbon dioxide which rapidly replaces the oxygen in the sealed containers. Once oxygen is exhausted, pests die, and fungi cannot spread.²⁰ PICS bags were developed to provide farmers with a chemical-free and cost-effective storage method for storing grain, improving food security, and allowing farmers to access better grain prices during the lean season. Grains stored in hermetic bags without optimal moisture content will result in quality deterioration (germination loss) or the grain will turn into silage.²¹ In developing countries, most farmers store their seeds in traditional facilities that often fail to maintain seed quality effectively over long periods.^12,18,22,23

Commercial seed producers can preserve seeds in cold storage to maintain quality and increase longevity. Smallholder farmers typically store seeds in ambient conditions for short periods. Different packaging materials like Polypropylene (PP) bags, Purdue Improved Crop Storage (PICS), and Super GrainPro bags are used by some model farmers and early generation seed (EGS) producers. However, identifying appropriate packaging materials that can maintain seed quality for extended periods under combined cold and ambient storage environments is crucial. Seed quality, including viability and vigor, decreases as the storage period increases under ambient storage condition due to seed aging. Research on open-pollinated maize seeds stored under cold storage conditions for EGS producers and suppliers in the study areas is lacking. Previous studies have focused on improving grain storage technologies for medium (12 months) storage period under ambient conditions.⁹ However, the current study focused on the improving storage technologies for open-pollinated maize genotypes stored for long-term under cold and ambient conditions. Limited information available on the combined effects of storage environments and packaging types on the specific stored open-pollinated maize seed quality that are commonly used by maize breeders, EGS producers and smallholder farmers. This study hypothesized that hermetic bags under cold storage would better maintain germination and vigour over 24 months than PPW under the same conditions. This study aims to investigate the combined effects of different storage environments and packaging types (hermetic and non-hermetic bags) on stored open-pollinated maize seed quality for 24 months. The research was also help to identify the best combinations to preserve seed quality for extended periods.

2. Materials and methods

2.1. Description of experimental site

The experiment was conducted for two years from 2021 to 2022 at Melkassa Agricultural Research Center in the Seed Research and Quality Control laboratory, Melkassa, Ethiopia. It is located at 8.402° North and 39.351° East with an altitude of 1550 meters above sea level (m.a.s.l.) in the Central Rift Valley of Ethiopia. The long-term annual average rainfall is 824.3 mm with erratic distribution. However, about 67% of the total rainfall in the area falls mainly from June to September with peaks in July and August.²⁴ The annual average minimum and maximum temperatures for the center are 13.80 °C and 28.10 °C, respectively.²⁵ The experimental area is categorized as arid to semi-arid agro-ecologies.

2.2. Meteorological data

Seed longevity is highly influenced by temperature and relative humidity (RH). Temperature and relative humidity (RH) data used in this study were obtained from the Climate, Geospatial, and Biometrics Research Department (CGBRD) (2021-2022), which is the officially recognized weather monitoring station located within the Melkassa Agricultural Research Center (MARC) and installed in the field near the seed storage room. The primary data were recorded daily using standard instruments placed inside the seed storage room for comparison with secondary data taken from CGBRD. The data were compared, and no significant variations were observed between the field and within the seed storage room. Finally, in this study, primary data recorded inside the seed storage room were used for analysis. Daily and annual records of key climatic variables, such as minimum and maximum room temperatures, minimum and maximum relative humidity, and annual averages of temperature and relative humidity parameters, were collected over the study periods. Open-pollinated maize seeds were stored in cold and ambient storage rooms. The temperatures and relative humidities of the cold storage room are fixed, while those in the ambient storage room fluctuate throughout the storage periods.

2.2.1. Ambient storage environment

Daily ambient temperature and relative humidity inside the storage room were monitored throughout the storage period. Maximum and minimum temperatures, and relative humidity were measured using a Testo 625 Digital Thermo-hygrometer. The instruments were placed approximately 1-1.5 m above the floor inside the storage room, away from direct sunlight and heat sources to ensure representative measurements of the storage environment. Minimum temperature and morning relative humidity were recorded at 06:00 hour, while maximum temperature and afternoon relative humidity were recorded between at 15:00 hour. The thermometer was reset after each observation to record the next day’s values. These measurements were taken daily to monitor environmental fluctuations under ambient storage conditions that may influence seed quality during the storage period.

2.2.2. Temperature

Temperature and relative humidity are the most significant factors that affect the quantity and quality of maize seeds during production and storage. Maize seed varieties were stored in ambient and cold rooms at MARC in seed research and quality control store rooms. The average temperature at which maize seeds were stored in ambient condition was recorded from January to September for two years. In 2021, the annual average temperature ranged from 14.27 to 28.57 °C for the ambient environmental system, with recorded minimum and maximum temperatures of 9.40 and 32.20 °C, respectively (Figure 1). In 2022, the annual average temperature ranged from 13.97 °C to 29.51 °C for the ambient environmental condition, with recorded minimum and maximum temperatures of 9.93 and 32.59 °C, respectively (Figure 2). The temperature in the cold storage room was maintained at 5 ±3 °C.

Figure 1.

Meteorological data for 2021 cropping season.

Figure 2.

Meteorological data for 2022 cropping season.

2.2.3. Relative humidity (RH)

The average relative humidity of the ambient environmental condition was recorded for two years. In 2021, the relative humidity fluctuated from 47% to 75% for the ambient environmental condition (Figure 1), while in 2022, it fluctuated from 40.10% to 70.13% for the ambient environmental system (Figure 2). The mean annual relative humidity in the ambient storage condition was 59.42% in 2021 and 53.71% in 2022. The relative humidity (RH) in the cold room storage was maintained at 42 ±3%.

2.3. Experimental treatments set up and design

The study consisted of cold and ambient storage conditions; three seed packaging materials (Polypropylene woven (PPW) bags, Super GrainPro (SGPr) bags, and Purdue Improved Crop Storage (PICS) bags, and three open pollinated maize varieties (Melkassa-2, Melkassa-4, and Melkassa-6Q) were selected to test seeds five times every six months (0, 6, 12, 18, and 24) for 24 months. The treatment combinations were arranged as 2*3*3 for a 24 month storage period. However, the arrangement of treatment combinations was determined depending on the treatment interactions incase where storage periods were taken as a factor. The seed quality testing parameters were laid out by Completely Randomized Design (CRD) with factorial arrangement by three replications in the seed technology and quality control laboratory, MARC, Ethiopia.

2.4. Open-pollinated maize varieties

Seed samples of Melkassa-2, Melkassa-4, and Melkassa-6Q are open-pollinated maize varieties used for storage. These open-pollinated maize varieties are popular and repeatedly used for both grain and seed production in the study areas. These maize varieties are released from Melkassa Agricultural Research Center (MARC) for semi arid agro-eclogies. They have different genetic chracteristics, while Melkassa-6Q genotype is a quality protein open-pollinated maize (protein dense genotype).

2.5. Packaging materials

Polypropylene woven bags (without polyethylene plastic layer, 50 kg capacity) were obtained from the Ethiopian local market in Adama City. The Super GrainPro (SGPr) bags™ (with single polyethylene plastic layer, 50 kg capacity) and Purdue Improved Crop Storage (PICS) bags^® (with double polyethylene plastic layer, 50 kg capacity) were purchased from HiTEC Trading House PLC and Shayashone Trading PLC, respectively, in Addis Ababa, Ethiopia. Each variety was packaged in each type of packaging material. PICS bags consist of two high-density polyethylene (HDPE) liners fitted inside a PP woven bag. The Super GrainPro bags™ developed by GrainPro are made of a thin single multi-layered plastic liner suitable for subsistence farmers. It is transparent and has low oxygen permeability.

2.6. Storage temperature and relative humidity

Storage conditions included cold and ambient storage rooms. The cold storage room temperature was set at 5 ±3 °C with a relative humidity (RH) of 42 ±3%. In 2021, the mean annual temperature ranged from 14.27 °C to 28.57 °C, while in 2022, it ranged from 13.97 °C to 29.51 °C for the ambient environmental condition. The mean annual relative humidity at the ambient storage condition in 2021 was 59.42%, whereas in 2022, it was 53.71%. Hermetic containers meliorate the storability of seeds with low moisture content, following the thumb rule proposed by Harrington that the sum of temperature in Fahrenheit and relative humidity in percentage should be less than 100. The safe relative humidity for seed storage is 40%.²⁶

2.7. Seed sources and sampling systems

Early generation seeds (EGS) of open pollinated maize produced in 2020 by the Sources Technology Multiplication and Seed Research department at Melkassa Agricultural Research Center. Seed samples were taken from three different seed lots of stored open-pollinated maize varieties. Initial seed quality testing was carried out by taking samples from each bag before sealing. Seed samples were taken from each treatment at six-month intervals for 24 months. The seed sample taking system involved opening and resealing bags, which was a dominant practice of seed producers and farmers in the country, particularly in the study areas.

2.8. Experimental procedures

Seed samples used for storage for quality analysis were taken from early generation seeds produced by Melkassa Agricultural Research Center to supply initial technology for seed producers. The moisture contents of the seed samples were measured before and after the seeds were dried in the open sun for three days to correspond with the prescribed national seed quality standards set for open-pollinated maize seeds (13%). The seeds were cleaned first by machine and then manually sorted to remove any extraneous materials. The seed of each variety was homogenized before storage and 25 kg of seeds were poured into each seed packaging material. Seed samples were taken from clean seed lots and quality parameters, such as purity components, moisture contents, germination and vigour tests were done at the commencement during storage and at six-month intervals for two years. Ambient and cold storage conditions were selected for maize seed storage. The temperature in the cold storage room was adjusted to 5 ±3 °C, whereas relative humidity ranged from 42% to 45%. The minimum, maximum and relative humidity of the ambient storage condition were recorded for two years (Figures 1 and 2). Seed packaging materials i.e., Polypropylene woven (PPW) bags, Super GrainPro (SGPr) bags, and Purdue Improved Crop Storage (PICS) bags, were selected and prepared to pour and store maize seeds. Lastly, 25 kg of cleaned maize seeds of each variety was poured into bags, sealed and stored. Initial seed quality testing was carried out by taking samples from each bag before sealing. Each bag contained seed samples that were sealed and stored in cold and ambient storage rooms. Seed samples were taken from each treatment at regular intervals of six-months for 24 months. After a six-month storage period, each bag was opened and the seed samples were taken for quality analysis. After the seed samples were taken from the opened bags, the headspace air of the opened hermetic bags was carefully expelled before resealing. The bags were then resealed and placed back to a prepared area in the storage room.

2.9. Data collection

Data on seed quality parameters such as physical purity components (%), seed moisture content (%), 1000-seed weight (g), standard germination (%), seedling dry weight (g), and seedling vigour index II were collected. Temperature and humidity data were recorded.

2.10. Seed quality test parameters

2.10.1. Physical purity test

During and after storage, one kilogram (1 kg) of open pollinated maize seed samples were taken from each variety and from this sample, 0.9 kg of the working sample of each maize variety was subjected to seed quality testing whereas 0.1 kg of each variety was stored for re-test if any mistake or doubt occurred in the tested results. Each working sample was divided into two equal portions (0.45 kg each) for physical purity analysis. The working samples were separated into pure seeds, inert matters and other seeds and each component was weighed using sensitive balance (CY224 SAM Technologies) with measuring capacity of minimum 0.0001g and maximum 220 g. Finally, the percentage composition of the seed lot was calculated based on the weight of each component.²⁷

Purity (%) = \frac{Weight of pure seed}{Weight of total sample} \times 100

2.10.2. Seed moisture contents

The seeds moisture contents were measured directly by using portable calibrated digital moisture meter (model GEHAKA G610, manufactured by Appliances, Electrical, and Eletronics Gehaka Ltd a company in Sao Paulo-SP, Brizil). Quality evaluation of seeds was tested by measuring three times successive measurements as replications during and after seed storage by six months intervals. Initially all maize seed lots had more than 16% moisture content when samples were taken for testing before storing. Then the samples were exposed to morning and afternoon sunlight by evenly distributing seeds on the canvas for three days to reduce the moisture content to allowed maximum level. During initial seed storage period three maize varieties stored at various moisture content level. The stored seeds of maize varieties had different moisture content since they were taken from different seed lots and genotypes. Conditioned different seed lots and different genotypes to uniform percentage of moisture content were difficult for maize seeds. However, the maximum safe moisture content for maize seed is 13% set by national seed quality standard.

2.10.3. Thousand seed weight

Thousand seed weight of each sample was determined by counting the entire working sample by seed counter machine. After seeds were counted, the samples were weighed in grams to the same number of decimal places used by KERN balance or sensitive balance as in the purity analysis. The whole working samples were put through the machine and the number of seeds on the indicator was read. The weights of 1000 seeds were calculated from the weight of the whole working samples.²⁷

2.10.4. Germination percentage

A germination test was done for all seed samples collected from each variety stored in different seed packaging materials under cold and ambient storage conditions. The pure seed, separated during purity analysis was considered for this test. Two hundred maize seeds were divided into four replicates of fifty seeds each and planted in sand substrata at ambient room temperature. The first count was made on the 4^th day whereas the final count was carried out on the 7^th day.²⁷ On the final day of the germination test, seedlings were evaluated into normal seedlings, abnormal seedlings, dead seeds and hard seeds components. For each seed sample, the result was expressed as the mean percentage of normal seedlings. To calculate the percentage of normal seedlings, abnormal seedlings, dead seeds and hard seeds where the following equation was used to get germination percentage of seeds.

Germination (%) = \frac{Number of normal seedlings}{Total number of seeds planted} \times 100

2.10.5. Seedlings dry weights

The seedling’s dry weight was measured after the final count of the standard germination test. Ten seedlings were randomly taken from each replicate and put in envelope to balance dry weight. After seedlings have dried in the oven dry the dry matter was weighed to the gram and the average seedlings dry weight was calculated. Ten seedlings were randomly taken from each replicate and appropriately placed in the envelope and dried in an oven at 80 °C for 24 hours. Lastly, the dry matter was weighed using sensitive balance and the average seedling dry weight was calculated.

2.10.6. Seedlings vigour index I

Vigour index I was calculated from each sample. Vigour index I was calculated by multiplying the means of standard germination with the average sum of shoot length and root length, while vigour index II was calculated by multiplying means of standard germination with seedlings dry weight.²⁸

2.11. Data analysis

The analysis of variances (ANOVA) was conducted using a Completely Randomized Design (CRD) with a factorial arrangement replicated three times. The 2×3×3 treatment combinations of data corresponding to two storage environment treatments, three packaging types and three open pollinated maize varieties were subjected to three-way ANOVA using SAS version 9 (SAS Institute Inc., Cary, NC, USA). Depending on the treatment interactions and the objective of the study, if the three-way interaction is significant, the best approach in this case is to compare the two interactions (storage environment treatments × packaging types) across the levels of the third factor which is the storage period. The two-way interaction between storage environment and packaging type was analyzed at each level of the storage period to evaluate the simple effects at 0, 6, 12, 18, and 24 months of storage and evaluation periods. The ANOVA tables are attached with the revised manuscript. Post hoc analysis was conducted using Tukey’s honest significance difference at 5 %, 1% and 0.1% significance levels.²⁹

3. Results

3.1. Determination of initial maize seeds quality attributes

The physical purity of the varieties was 99% and above, which meets the minimum pure seed percentage set by national seed quality standards for open-pollinated maize of pre basic and basic seed classes.¹⁷ The ANOVA indicated that there was no significant variation perceived among maize varieties regarding moisture content. At the initial storage period, the seed moisture content of maize varieties ranged from 13.85% to 14.17%. However, the safe maximum moisture content of national seed quality standards for open-pollinated maize seed is 13%. At the initial storage period, significant (P≤0.05) difference was observed between open-pollinated maize varieties of Melkassa-2 (276.33 g), Melkassa-4 (276 g) and Melkassa-6Q (227.67 g) in thousand seed weight. The results of the initial mean percentage of seed germination indicated that there was no significant differences observed among maize crop varieties. The mean percentage of standard germination for each maize variety of Melkassa-2, Melkassa-4 and Melkassa-6Q were 93.33%, 92% and 91.33% respectively. These results are above the minimum germination standard and hence, increase the acceptance of tested seed lots by regulatory approval.

3.2. Determination of seed moisture content

The ANOVA indicated that high significant (P≤0.001) differences were observed between open-pollinated maize seeds and storage conditions after six and twelve months of storage. However, no significant differences were observed within packaging materials in termes of seed moisture content. After twenty-four months of storage, significant differences (P≤0.01) were observed between open-pollinated maize seeds and storage conditions in moisture content, while no significant differences were found within seed packaging materials throughout the storage periods except at the initial stage. Within twelve months of storage, high significant differences (P≤0.001) were observed between storage conditions and maize seeds. Significant differences (P≤0.01) were observed between storage conditions, and significant (P≤0.05) differences were observed between maize varieties after eighteen months of storage. After twenty-four months of storage, significant (P≤0.01) differences were observed between storage conditions and maize varieties. Interaction effects between storage conditions and maize varieties were highly significant (P≤0.01) at the initial and after six-month storage period, while no significant interaction effects were observed between storage conditions and seed packaging materials, maize varieties and seed packaging materials, or storage conditions, seed packaging materials and maize varieties throughout the storage periods (Table 1).

Table 1.

P-values that showed the level of significance for storage conditions (SC), maize crop varieties (CVs), seed packaging materials (PM) and their interactions in seed moisture content.

Sources of variations	df	Storage periods and P-values for seeds moisture contents
Sources of variations	df	Initial	6 months	12 months	18 months	24 months
Storage conditions (SC)	1	0.82	0.00***	0.00***	0.01*	0.00**
Crop varieties (CVs)	2	0.00***	0.00***	0.00***	0.03*	0.00**
Packaging materials (PM)	2	0.00***	0.42	0.79	0.72	0.73
SC*CVs	2	0.00***	0.00***	0.78	0.46	0.43
SC*PM	2	0.00***	0.69	0.73	0.94	0.97
CVs*PM	4	0.00***	0.99	0.97	1.00	1.00
SCCVsPM	4	0.00***	0.99	1.00	1.00	1.00
Means		14.20	14.38	14.22	14.04	13.94
CV		0.59	2.85	6.18	7.48	6.47
SD		0.3841	0.5440	0.8503	0.6417	0.7112
SEM		0.0905	0.1282	0.2004	0.1513	0.1676

Source/s: Own lab data (2021-2022).

Note. SC= Storage condition, CVs= Crop varieties, df= degree of freedom, CV= Coefficient of Variation, PM= Packaging materials, P values at 5% significant level.

The moisture content of open-pollinated maize seeds was significantly influenced by maize genotypes or varieties, packaging materials, and storage conditions, especially at six and twelve months of storage periods. Variations in genotypes and packaging materials consistently had significant effects over time, while differences in storage conditions became more pronounced after six-months. This indicates that the critical roles of both factors in long-term seed moisture stability. Significant differences were observed between maize seed lots or varieties at the initial storage in moisture content.

Seed moisture content stored in both cold and ambient storage conditions were fluctuated. The mean percentage of moisture content stored in the cold store changed from 14.20% to 14.35% at the initial and after twenty-four months of storage, respectively. The moisture content of Melkassa-6Q maize variety stored under the cold storage showed a high increment from the initial to twenty-four months of storage periods, as shown in Figure 3(c). This increment may be due to genetic variability in the maize crop variety, storage conditions, seed packaging materials, and the month or season of the germination test, where the temperature and relative humidity varied in the Centeral Rift Valley area, as shown in Figures 1 and 2. In contrast to seeds stored in the cold store, seeds stored under ambient storage conditions showed a faster reduction in moisture content from the initial (14.19%) to twenty-four months (13.35%) of storage periods overall, as shown in Figure 4. The moisture content of open-pollinated maize seeds stored in different seed packagings under cold storage decreased slightly compared to seeds stored in different seed packagings under ambient storage condition, except for the Melkassa-6Q variety, which increased, as shown in Figures 3(c) and 4(c).

Figure 3.

Interaction effects of packaging materials and storage periods on moisture content of open pollinated maize varieties under cold storage condition. (a) Interaction effects of ‘packaging material*storage period’ on moisture content of open pollinated melkassa-2 maize variety stored at cold storage condition, (b) Interaction effects of ‘packaging material*storage period’ on moisture content of open pollinated melkassa-4 maize variety stored at cold storage condition and (c) Interaction effects of ‘packaging material*storage period’ on moisture content of open pollinated melkassa-6Q maize variety stored at cold storage condition.

Figure 4.

Interaction effects of packaging materials and storage periods on moisture contents of open pollinated maize varieties under ambient storage condition. (a) Interaction effects of ‘packaging material*storage period’ on moisture content of open pollinated melkassa-2 maize variety stored under ambient storage condition, (b) Interaction effects of ‘packaging material*storage period’ on moisture contents of open pollinated melkassa-4 maize variety stored under ambient storage condition and (c) Interaction effects of ‘packaging material*storage period’ on moisture contents of open pollinated melkassa-6Q maize variety stored under ambient storage condition.

3.3. Determination of thousand seeds weight

The ANOVA revealed that high significant interaction effects (P≤0.001) were observed between ‘storage condition×open-pollinated maize variety’, and ‘storage condition×packaging materials×storage condition’, and ‘packaging materials × maize crop varieties’ on the mean weight of 1000-seeds within twelve months of the storage period as summarized in Table 2. At the twelve month storage period, significant interaction effects (P≤0.001) were observed between ‘storage conditions×maize varieties×seed packaging materials’ in 1000-seed weight. Additionally, significant interaction effects (P≤0.001) were observed between ‘storage condition×maize crop variety’ and ‘packaging material×maize crop variety’ in 1000-seed weight at the initial stage. However, no interaction effects were observed between ‘storage condition×packaging material’ regarding 1000-seed weight initially. Also, no interaction effects were observed between ‘storage condition×packaging material’ at the initial and after six, eighteen and twenty four months of storage periods interms of 1000-seed weight (Table 2). Highly significant differences (P≤0.001) were observed among open-pollinated maize varieties in terms of 1000-seed weight after six, twelve, eighteen, and twenty-four months of storage periods. In general, the 1000-seed weight of open-pollinated maize was significantly influenced by the interaction of storage conditions × maize varieties × packaging materials, particularly during the first twelve months of storage. Significant interactions were observed between storage condition × maize variety, and packaging material × maize variety, including a three-way interaction at twelve months. However, the interaction between storage condition × packaging material alone had no significant effect on 1000-seed weight across the evaluated storage periods.

Table 2.

P-values of storage conditions (SC), maize crop varieties (CVs), seed packaging materials (PM) and their interactions in thousand seeds weight.

Sources of variations	df	Storage periods and P-values for thousand seed weight
Sources of variations	df	Initial	6 months	12 months	18 months	24 months
Storage conditions (SC)	1	0.00***	0.82	0.72	0.43	0.11
Crop varieties (CVs)	2	0.00***	0.00***	0.00***	0.00***	0.00***
Packaging materials (PM)	2	0.02*	0.10	0.00***	0.56	0.90
SC*CVs	2	0.00***	0.10	0.00***	0.26	0.41
SC*PM	2	0.14	0.16	0.00***	0.88	0.81
CVs*PM	4	0.00***	0.34	0.00***	0.93	0.98
SCCVsPM	4	0.10	0.22	0.00***	1.00	0.97
Means		260	258.84	255.18	251.63	249.04
CV		0.72	2.83	2.00	2.92	4.17
SD		23.702	22.772	21.889	23.299	24.179
SEM		5.587	5.367	5.159	5.492	5.699

Source/s: Own lab data (2021-2022).

Note. SC= Storage condition, df= degree of freedom, CVs= Crop varieties, PM= Packaging materials, P-values at 5% significance level.

The Melkassa-2 variety stored in PICS, PPW, and Super GrainPro bags in a cold storage room had a higher 1000-seed weight than the other two maize seeds stored in the same packaging materials under cold and ambient storage conditions after twenty-four months (Table 3).

Table 3.

Means interaction effects of ‘storage condition×maize variety×packaging types’ in thousand seed weight (g).

Storage conditions	Varieties	Bag type	0 Month	6 Months	12 Months	18 Months	24 Months
Cold (5±3˚C)	Melkassa-2	PPW bag	280.58a	286.30a	273.80a	274.87a	273.70a
Cold (5±3˚C)	Melkassa-2	SGPr bag	281.60a	275.40ab	273.80a	274.07a	270.03a
Cold (5±3˚C)	Melkassa-2	PICS bag	278.00ab	261.67b	273.80a	272.00a	273.83a
Cold (5±3˚C)	Melkassa-4	PPW bag	276.00ab	270.37ab	269.68a	260.50a	259.33a
Cold (5±3˚C)	Melkassa-4	SGPr bag	278.00ab	272.63ab	266.60a	265.97a	264.63a
Cold (5±3˚C)	Melkassa-4	PICS bag	274.00bc	270.67ab	222.10b	261.00a	260.17a
Cold (5±3˚C)	Melkassa-6Q	PPW bag	230.00d	234.50c	264.28a	220.80b	219.80b
Cold (5±3˚C)	Melkassa-6Q	SGPr bag	225.00d	227.60c	226.35b	221.67b	220.17b
Cold (5±3˚C)	Melkassa-6Q	PICS bag	228.00d	228.33c	228.50b	221.00b	220.50b
Ambient	Melkassa-2	PPW bag	273.80bc	281.83ab	273.73a	270.63a	267.53a
Ambient	Melkassa-2	SGPr bag	270.00c	281.13ab	271.17a	267.58a	264.00a
Ambient	Melkassa-2	PICS bag	274.00bc	281.00ab	269.00a	266.67a	264.33a
Ambient	Melkassa-4	PPW bag	276.00ab	269.90ab	265.77a	265.95a	266.13a
Ambient	Melkassa-4	SGPr bag	278.00ab	267.73ab	273.07a	266.90a	260.73a
Ambient	Melkassa-4	PICS bag	274.00bc	268.33ab	266.00a	262.83a	259.67a
Ambient	Melkassa-6Q	PPW bag	230.00d	225.63c	225.13b	219.03b	212.93b
Ambient	Melkassa-6Q	SGPr bag	225.00d	229.70c	227.13b	220.35b	213.57b
Ambient	Melkassa-6Q	PICS bag	228.00d	226.33c	223.33b	217.50b	211.67b
HSD 5%			5.72	22.40	15.61**	22.50	31.82
CV			0.72	2.83	2.00	2.92	4.17
Means			260.00	258.84	255.18	251.63	249.04
SD			23.70	22.77	21.89	23.30	24.18
SEM			5.59	5.37	5.16	5.49	5.70

Source/s: Own lab data (2021-2022).

Note. Means within a column followed by the same letter are not significantly different from each other at 5% P level based on Tukey’s HSD test. PPW= Polypropylene Woven, SGPr= Super GrainPro, PICS= Purdue Improved Crop Storage, SD= Standard deviation, SEM= Standard error of mean.

3.4. Determination of germination percentage

The ANOVA indicated that high significant (P≤0.001) differences were observed between maize crop varieties in standard germination at initial storage. Significant (P≤0.001) differences were observed after six months, twelve months, and eighteen months of storage periods observed between storage conditions in standard germination (Table 4). Significant interaction variations were observed between ‘storage conditions × maize crop varieties’ in standard germination after eighteen and twenty four months of storage periods. Significant (P≤0.05) interaction effects observed between ‘maize crop varieties × packaging materials’ after eighteen months of storage period in standard germination. The mean percentage of standard germination indicated that significant interaction effects (P≤0.05) were observed between storage condition, maize crop seed, and packaging material after eighteen and twenty four months of storage periods. However, no interaction effects were observed between storage conditions and packaging materials on seed germination throughout the storage periods (at initial, 6, 12, 18 and 24 months) (Table 4).

Table 4.

P-values for storage periods, storage conditions (SC), maize crop varieties (CVs), packaging materials (PM) and their interactions in seed germination.

Sources of variations	df	Storage periods and P-values for standard germination
Sources of variations	df	Initial	6 months	12 months	18 months	24 months
Storage conditions (SC)	1	1.00	0.00***	0.05*	0.01**	0.15
Crop varieties (CVs)	2	0.00***	0.08	0.27	0.07	0.46
Packaging materials (PM)	2	0.17	0.31	0.66	0.57	0.84
SC*CVs	2	1.00	0.11	0.22	0.00**	0.01*
SC*PM	2	1.00	0.47	0.75	0.23	0.16
CVs*PM	4	0.38	0.76	0.25	0.05*	0.37
SCCVsPM	4	1.00	0.85	0.81	0.02*	0.02*
Means		91.96	90.30	85	80.65	76.30
CV		1.51	8.78	13.27	8.56	14.64
SD		1.0556	7.9449	6.8305	7.1794	9.4560
SEM		0.2488	1.8726	1.6100	1.6922	2.2288

Source/s: Own lab data (2021-2022).

Note. SC= Storage condition, df= degree of freedom, CVs= Crop varieties, PM= Packaging materials, P-values at 5% significant level.

After twenty-four months of storage, Melkassa-2 and Melkassa-4 seeds packed in SGPr bags, and Melkassa-4 packed in PICS bags stored under cold storage conditions (Figure 5) showed lower germination percentages than Melkassa-2, Melkassa-4 and Melkassa-6Q stored in the same packaging materials under ambient storage condition (Figure 6). After 24 months of storage, Melkassa-2 seed packed in PPW and PICS bags, Melkassa-4 and Melkassa-6Q seeds packed in PPW, SGPr, and PICS bags stored under cold storage showed higher germination percentages than Melkassa-2, Melkassa-4, and Melkassa-6Q seeds packed in the same packaging materials stored under ambient storage condition as shown in Figures 5 and 6. The Melkassa-6Q maize variety stored in PICS bags under cold storage room showed a higher germination percentage (90.67%) compared to seeds stored in the same packaging materials (65.33%) in ambient storage condition for 24 months as shown in Figures 5 and 6. Melkassa-6Q maize variety stored in PICS bags in cold storage condition after 24 months of storage showed a higher germination percentage (90.67%) compared to the germination percentage of maize seed stored in the same packaging for 18 months of storage (Figure 5). However, the difference between them was not significant. Melkassa-4 seed stored in PICS bags under cold storage condition showed a higher germination percentage (89.33) compared to seed stored under ambient storage condition (62.67%) after 24 months of storage. Consequently, seed producers can store their open-pollinated maize seeds under cold storage in PICS, Super GrainPro, and Polypropylene woven bags for 24 months of storage before falling below the minimum national standard set for open-pollinated maize seed germination (85%). This might be due to several factors, such as season of germination test where the temperature and relative humidity showed high fluctuation (Figures 1 and 2), storage conditions, composition of seed packaging materials and genetic variability of maize crop varieties.

Figure 5.

Interaction effects of packaging materials and maize varieties stored for 24 months under cold storage condition on standard germination. (a) Interaction effects of ‘packaging material*storage period’ on standard germination of open pollinated melkassa-2 maize variety stored at cold storage condition, (b) Interaction effects of ‘packaging material*storage period’ on standard germination of open pollinated melkassa-4 maize variety stored at cold storage condition and (c) Interaction effects of ‘packaging material*storage period’ on standard germination of open pollinated melkassa-6Q maize variety stored at cold storage condition.

Figure 6.

Interaction effects of packaging materials and maize varieties stored for two years under ambient storage condition on standard germination. (a) Interaction effects of ‘packaging material*storage period’ on standard germination of open pollinated melkassa-2 maize variety stored at ambient storage condition, (b) Interaction effects of ‘packaging material*storage period’ on standard germination of open pollinated melkassa-4 maize variety stored at ambient storage condition and (c) Interaction effects of ‘packaging material*storage period’ on standard germination of open pollinated melkassa-6Q maize variety stored at ambient storage condition.

3.4.1. Cold storage condition

Seed germination of open-pollinated maize declined more slowly under cold storage compared to ambient condition. Melkassa-2 seed stored in SGPr, PICS, and PPW bags showed faster germination reduction from 18 to 24 months, while Melkassa-4 stored in PPW declined rapidly from 6 to 18 months but stabilized afterwards. Melkassa-6Q seed stored in SGPr and PPW bags declined rapidly, while stored in PICS bags showed gradual reduction across 24 months (Figure 5(a)–(c)). Overall, cold storage maintained seed quality better compared to ambient storage condition. Purdue Improved Crop Storage bags were recommended for Melkassa-2, Melkassa-4 and Melkassa-6Q seeds to preserve seeds for a long-term storage. Also PPW bags were recommended to preserve Melkassa-2 seed for long storage. Generally, germination of seeds stored in a cold room decreased more slowly as storage period increase compared to seeds stored under ambient storage condition regardless of packaging materials and maize varieties (Figure 5).

3.4.2. Ambient storage condition

Germination of open-pollinated maize seeds declined more rapidly under ambient storage condition. Germination of Melkassa-2 seed stored in PPW and PICS bags decreased consistently, while in SGPr showed early reduction followed by slight increase and decrease variability. Germination of Melkassa-4 seed stored stored in PPW bags declined rapidly in the first 6 months, while stored in SGPr and PICS bags showed variations but overall reduction with the incement of storage time. Germination of Melkassa-6Q seed stored in PICS bags declined quickly, while stored in SGPr maintained higher germination compared to other packagings (Figure 6(a)–(c)). Generally, ambient storage condition caused varied germination trends. Super GrainPro bags were recommended to sore Melkassa-2 and Melkassa-6Q seeds, while PPW for Melkassa-4. Again SGPr bags were recommended to store Melkassa-6Q seed followed by PICS bags for long-term storage. Germination of seeds stored under ambient storage condition in SGPr bags showed zigzag variation with the increment of storage period (Figure 6). Under ambient storage condition, SGPr bags were recommended to store Melkassa-2 variety followed by PPW bags, while PPW bags were recommended to store Melkassa-4 variety followed by SGPr bags, and PPW bags were recommended to store Melkassa-6Q seeds in the absence of SGPr and PICS bags.

3.5. Determination of seedlings dry weight

The means of seedling dry weight decreased slightly from the first month of storage to the final month. The results revealed that significant interaction effects (P≤0.05) were observed between storage conditions, maize varieties and packaging materials in seedlings dry weight at initial and final storage periods. The average seedling dry weight varied from 0.79 g to 0.91 g between the initial and final storage durations (Table 5).

Table 5.

Means interaction effects of ‘storage conditions×maize varieties×packaging types’ in seedlings dry weight at initial and after two years storage longevity.

Storage conditions	Varieties	Bag type	Initial (SDW) (g)	Final (SDW) (g) (at 24^th month)
Cold (5±3˚C)	Melkassa-2	PPW bag	0.97ab	0.85ab
Cold (5±3˚C)	Melkassa-2	SGPr bag	0.92cd	0.80de
Cold (5±3˚C)	Melkassa-2	PICS bag	0.98a	0.86ab
Cold (5±3˚C)	Melkassa-4	PPW bag	0.95abc	0.83bcd
Cold (5±3˚C)	Melkassa-4	SGPr bag	0.91cd	0.79e
Cold (5±3˚C)	Melkassa-4	PICS bag	0.82e	0.70f
Cold (5±3˚C)	Melkassa-6Q	PPW bag	0.91cd	0.79e
Cold (5±3˚C)	Melkassa-6Q	SGPr bag	0.92cd	0.80de
Cold (5±3˚C)	Melkassa-6Q	PICS bag	0.99a	0.87a
Ambient	Melkassa-2	PPW bag	0.89d	0.77e
Ambient	Melkassa-2	SGPr bag	0.95abc	0.84abc
Ambient	Melkassa-2	PICS bag	0.81e	0.69f
Ambient	Melkassa-4	PPW bag	0.91cd	0.79e
Ambient	Melkassa-4	SGPr bag	0.93bcd	0.81cde
Ambient	Melkassa-4	PICS bag	0.99a	0.87a
Ambient	Melkassa-6Q	PPW bag	0.82e	0.70f
Ambient	Melkassa-6Q	SGPr bag	0.89d	0.77e
Ambient	Melkassa-6Q	PICS bag	0.84e	0.72f
HSD 5%			0.047*	0.037*
CV			1.69	1.52
Means			0.9111	0.7917
SD			0.0579	0.0583
SEM			0.0136	0.0137

Source/s: Own lab data (2021-2022).

Note. Means within a column followed by the same letter are not significantly different from each other at 5% probability level based on Tukey’s HSD test. PPW= Polypropylene Woven, SGPr= Super GrainPro, PICS= Purdue Improved Crop Storage, SDW= Seedlings dry weight, SD= Standard deviation, SEM= Standard error of mean.

3.6. Determination of seedlings vigour vndex-I

Among the physiological seed quality test parameters, vigour indices are very crucial. Both vigour index-I and II are used to evaluate seed vigour. In this experiment vigour index-I is used to evaluate seed vigour. The overall seed performance, or computed vigour index-I, has been regarded as a good measure to evaluate the quality of seed lots. The results indicated that there were significant (P≤0.05) interaction effects of ‘storage conditions×maize varieties×packaging types’ regarding vigour index-I initially before seed storage and after seeds have been stored for 24 months (Table 6). Regardless of seed treatments, the vigour of stored seed gradually declined as the storage period advanced. The average seedling vigour index-I at the start and end of storage decreased from 83,855 to 60,915. The decline in the vigour index could be caused by the decrease in germination and seedling dry weight. At the start and end of the storage period, the seedling vigour index-I fluctuated considerably. After 24 months of storage longevity, the seedling vigour index-I was considerably greater in Melkassa6Q (78,886) seeds stored in a cold storage room in PICS bags compared to Melkassa-6Q (47,041) seeds stored in an ambient storage room at the end of the 24-month storage period (Table 6).

Table 6.

Means interaction effects of ‘storage conditions×maize varieties×packaging materials’ in seedling vigour index-I at initial and after two years storage longevity.

Storage conditions	Maize varieties	Packaging materials	VGI-I at initial	VGI-I in 24 months
Cold (5±3˚C)	Melkassa-2	PPW bag	89895	74803
Cold (5±3˚C)	Melkassa-2	SGPr bag	85565	60803
Cold (5±3˚C)	Melkassa-2	PICS bag	91802	73387
Cold (5±3˚C)	Melkassa-4	PPW bag	86769	65299
Cold (5±3˚C)	Melkassa-4	SGPr bag	84335	58993
Cold (5±3˚C)	Melkassa-4	PICS bag	74896	43872
Cold (5±3˚C)	Melkassa-6Q	PPW bag	82205	58993
Cold (5±3˚C)	Melkassa-6Q	SGPr bag	83725	60803
Cold (5±3˚C)	Melkassa-6Q	PICS bag	90758	78886
Ambient	Melkassa-2	PPW bag	82481	56467
Ambient	Melkassa-2	SGPr bag	89285	73923
Ambient	Melkassa-2	PICS bag	75878	41403
Ambient	Melkassa-4	PPW bag	83115	61094
Ambient	Melkassa-4	SGPr bag	86188	62641
Ambient	Melkassa-4	PICS bag	90422	77720
Ambient	Melkassa-6Q	PPW bag	74076	43872
Ambient	Melkassa-6Q	SGPr bag	80995	56467
Ambient	Melkassa-6Q	PICS bag	77005	47041
HSD 5%			27.01*	18.26*
CV			0.01	0.01
Means			83855.28	60914.83
SD			5619.24	11748.21
SEM			1324.47	2769.08

Source/s: Own lab data (2021-2022).

Note. Means within a column followed by the same letter are not significantly different from each other at 5% probability level based on Tukey’s HSD test. PPW= Polypropylene Woven, SGPr= Super GrainPro, PICS= Purdue Improved Crop Storage, VGI= Vigor index, SD= Standard deviation, SEM= Standard error of mean.

Maize seed germination testing follows standard seed testing procedures used in International Seed Testing Association (ISTA) seed laboratories. Seed germination is a key factor in determining the quality of seed lots under laboratory conditions. The normal germination rate of maize seeds is 70% or higher, which allows seeds to be used for commercial purposes. However, this rate alone is not sufficient to estimate the performance of seeds in field conditions. Vigour indices are essential for estimating the field emergence of maize seed lots. Seed lots with higher values of vigour index-I, which combines standard germination with seedling dry weight, are likely to perform well in the field. The vigour index-I test is a simple and efficient way for seed producers and suppliers to estimate the quality of seed lots under both laboratory and field conditions. Consequently, regulatory bodies should add the vigour index-I test parameter when testing quality of various seed samples for quality assurance and certification systems, supporting reliable maize seeds establishment and productivity.

4. Discussion

The quality of open-pollinated maize seeds stored under cold and ambient environments within Polypropylene woven bags, Super GrainPro bags and Purdue Improved Crop Storage bags over a 24-month period. This research was prompted mainly by the annual rejection of large quantities of produced early generation seed (EGS) by the quality control authority, possibly due to either quality deterioration of measured seed falling below the set quality standards for EGS or techniques of analysis. The combined analysis focused on the specific timeframe to investigate and address the observed seed quality issues.

4.1. Determination of initial maize seed quality attributes

The initial quality assessment revealed that all maize varieties met national seed quality standards for physical purity and germination, though their moisture contents were slightly above the prescribed limit. The minimum percentages of physical purity of pure seeds, seed moisture contents and seed germination prescribed for open-pollinated maize certified four (C4) seed class by the national seed quality standard authority are 98, 13 and 80 respectively.³⁰ Thousand seed weight varied significantly among varieties, while germination remained consistently high across them. The dry weight of seedlings varied from 0.81 g to 0.998 g initially.

4.2. Determination of seed moisture content

The mean percentage of seed moisture contents of open-pollinated maize (OPM) seeds varied from 13.67 to 14%. This variation may be due to the genetic diversity of maize crop varieties, storage conditions, packaging materials, storage periods and other external environmental factors. This finding is similar to the previous finding that reported the moisture content of the harvested seed is influenced by the surrounding relative humidity and the temperature conditions, the two major factors that control the storage shelf life of the seed in processing and storage.³¹ Open-pollinated maize seeds’ moisture contents decreased relatively as the storage period increased for both cold and ambient storage conditions except for the Melkassa-6Q variety, which increased. This may be due to the protein dense character of the variety. According to a previous study, quality protein maize has undesirable characteristics that reduce yield compared to normal maize, low grain consistency, and a farinaceous endosperm that retains water.³² The moisture contents of seeds stored in a cold storage room decreased slightly more than seeds stored under ambient storage conditions, regarding of varieties and packaging materials, except for Melkassa-6Q variety, which increased (Figures 3(c) and 4(c)). This may be due to the hygroscopic nature and nutrient contents of the variety in addition to other factors. This finding is agreed with the study conducted previously that reported features of protein maize result in a soft, chalky endosperm that dried slowly making it prone to damage, a thick pericarp, more susceptibility to diseases and pests, higher storage losses, and also affects harvest ability.³³ Again other studies corroborated with this finding revealed that the increase in moisture content of the seed up to six months of storage period might be due to the hygroscopic nature of the seed and moisture exchange in a previous material during high RH season.²⁶

4.3. Determination of thousand seeds weight

Highly significant interaction effects (P≤0.001) were perceived between ‘storage condition×seed packaging type×open-pollinated maize variety’ for the TSW after 12 months of storage. Low 1000-seed weights tend to result from poor grain fill and environmental conditions found in the field before harvest. The other factors for variation may be due to the genetic nature of varieties, seed packaging materials, storage conditions, seed age/storage longevity, and environmental dynamics. Among environmental factors temperature and relative humidity at which seeds stored are the major factors that affect maize seeds quality parameters, particularly 1000 seed weight. Maize crop varieties differ in seed size, number of seeds, and consequently, the amount of seed rates is also highly variable using 1000 seed weight. Seed producers can account for 1000-seed weight for seed size variations when calculating seeding rates, calibrating seed drills and estimating shattering and combine losses. Similar studies supported that the seed quality can be influenced by many different factors such as genetic features, nominal potential or sprouting potential, seed potential, humidity, storage quality, seed preservation, and seed healthy; but the most important ones are sprouting rates and seed potential.^34,35

4.4. Determination of germination percentage

The performance of stored seeds varied depending on the variety, moisture contents, packaging type, and storage condition within the storage periods. Notably, Melkassa-6Q stored in PICS bags under cold conditions achieved the highest germination rate (90.67%) after 24 months, surpassing seeds stored under ambient condition for the same storage periods. However, the differences were not statistically significant. Similarly, Melkassa-4 in PICS under cold storage exhibited superior germination (89.33%) compared to ambient storage (62.67%) after 24 months of storage period. Storing all OPM seeds in hermetic bags (PICS, SGPr) and non-hermetic bags (PPW) under cold conditions effectively preserved seed quality before falling below the minimum quality standard prescribed for certified four (C4). OPM seed class (80%) for 18 months, except M-4 stored in SGPr bag for 12 months and M6Q stored in PPW bag for less than 12 months. This finding is in agreement with the finding that stated the protective properties of packaging materials and genetic variation among maize varieties caused by the fluctuations in environmental factors.^36–38 This finding is corroborate with the finding that stated seeds stored in hermetic bags under ambient condition for 12 months with moisture content between 11% and 14% maintained higher germination rates compared to those stored in conventional containers.⁹

In the similar manner, study carried out on common bean seeds revealed that poor seed germination could result from poor preharvest seed management practices and post-harvest handling such as seed processings; particularly storage conditions.³⁹ This findings are in agreement with previous study that found hermetic bags kept significantly higher seed germination percentage with 94.2% at six 6 months of storage periods.⁴⁰ Proper packing materials and storage methods are essential for good seed storage stability. Generally, seed quality parameters decreased as storage period increase, irrespective of storage conditions, maize varieties, and packaging materials which were associated with the fluctuation of temperatures, seed moisture contents and seed aging. Sudy conducted previously reported that seed germination and seedling vigour declined significantly when seeds were stored at very high (95%) to high (75%) RH and 35 °C temperature while the electrical conductivity recorded a steep increase at these conditions implying their usefulness as indices for seed quality loss.⁴¹ A similarly, earlier study indicated that increasing the storage period after harvest until 9 months decreased significantly seed germination, seedling vigour, moisture content, oil%, and crude protein.⁴²

4.5. Determination of seedlings dry weight

The average seedlings dry weight varied from 0.79 g to 0.91 g between the initial and final storage duration. In agreement with the findings of the current work, the analyzed data on different genotypes of vegetable pea study revealed that seedling dry weight indicated a wide range of variability from 0.52 g to 0.94 g.⁴³ The population mean of pea seedlings dry weight was 0.73 g. After 24 month of storage duration, seedlings dry weight (g) of Melkassa-6Q and Melkassa-4 varieties (0.87g each) stored in PICS bags under cold and ambient store rooms respectively, showed a significant (P≤0.05) difference than other treatments (Table 5). Study conducted previously showed that the seedling vigour index and seedling dry weight was also more due to higher seedling length.⁴⁴ Seed lot having higher seedling dry weight considered to have higher vigour.⁴⁵ A study demonstrated that a wide range of variability in seedling dry weight of pea genotypes have also been varied from 0.42 g to 1.13 g.⁴⁶

4.6. Determination of seedlings vigour index I

The average seedling vigour index I of seeds stored in a cold storage room (63,982.11) showed a higher vigour index I than seeds stored at ambient storage conditions (57,847.56) after 24 months of storage, regardless of varieties and packaging types. Based on visual observation, storing seeds in hermetic bags in a cold room has a positive effect and may be useful for better seed storage, resulting in high-quality seeds with better performance under field conditions. Seed lots with higher seedling dry weight were considered to have a higher vigour.⁴⁵ A similar study reported by El-Sayed et al.⁴² indicated that increasing the storage period after harvest up to 9 months significantly decreased seed germination, seedling vigour, moisture content, oil percentage, and crude protein.

In summary, seeds stored in a cold storage room showed better results in terms of seed germination percentage, slight fluctuations in moisture content, and 1000-seed weight with no occurrences of insect populations or seed damage throughout the storage periods. Maize seeds stored at ambient conditions in a warehouse were used for early generation seeds (EGS) stored up to distribution for planting. The occurrence of insect pests was not a problem during the study, as the warehouse was fumigated every 10 to 15 days to control pests. Frequent application of phosphotoxine is important because the high temperature and relative humidity of the area accelerate the reproduction of insect pests. This is how maize early generation seeds are preserved and delivered to various stakeholders who use EGS for further multiplication, research activities, seed maintenance, emergencies, and to reduce seed shortages when needed. Furthermore, under the same storage conditions and over the same storage periods, the intensity of seed quality decline differs between maize crop varieties and packaging materials due to genetic diversity and the composition of packaging materials.

The moisture content of three popular maize varieties stored in three packaging materials (Polypropylene woven bags, SuperGrainPro bags, and PICS bags) under cold and ambient storage conditions (SC) for twenty-four months was summarized as discussed above. The moisture content of seeds stored under ambient storage conditions showed a gradual decline, except for the Melkassa-6Q variety stored in SuperGrainPro bags, which showed a slight increase. Similarly, the moisture content of seeds stored under cold storage conditions showed a gradual decline, except for the Melkassa-6Q variety stored in PPW, SGPr, and PICS bags, which increased from the initial to the end of the storage periods. Generally, seeds stored in PICS bags placed in a cold store showed significant superiority for most of the tested quality parameters over seeds stored in other packaging materials under ambient storage conditions, regardless of maize crop varieties. Future studies should focus on quantifying insect pests and diseases under various packaging and storage conditions to improve long-term storage recommendations. Additionally, research on different geographical locations and hybrid maize varieties is needed for seed producers. The moisture content for open-pollinated quality protein maize (QPM) and hybrid maize seed varieties should be evaluated under field and laboratory conditions.

4.7. Limitations of the study

The experiment included only three open-pollinated maize varieties and three types of packaging materials under specific cold and ambient storage conditions, which may limit the generalization of the findings to other open-pollinated maize genotypes, seed packaging materials, and environmental conditions. Since the study focused exclusively on open-pollinated maize seeds; further research is needed to evaluate hybrid and parental lines of maize genotypes or seeds under similar storage conditions and packaging materials for both short- and long-term storage. Under ambient storage conditions, insect infestation was controlled through frequent fumigation, which may not reflect typical farmer practices in seed storage management. The study also focused mainly on selected seed quality parameters and did not assess fungal contamination or seed health aspects. Moreover, the storage period was limited to 24 months and it did not assess the economic feasibility of different packaging materials and storage systems, which may influence their wider adoption.

5. Conclusion and recommendations

The quality of open-pollinated maize seeds is significantly affected by storage conditions, packaging materials, and storage durations. Hermetic packaging combined with cold storage conditions preserved seed quality best, maintaining higher germination, viability and vigour over 24 months compared to ambient storage. Despite some decline in quality over time, PICS bags are more effective in maintaining seed quality likely due to the double, and single polyethylene layers of the bags. Adopting hermetic storage systems is essential for prolonging seed shelf life and ensuring seed security in semi-arid regions. Cold storage is recommended in seed enterprises and cooperative unions to reduce quality loss, while hermetic storage in ambient conditions is effective when cold facilities are limited. PPW bags can be used as short-term alternatives but should not be used for long-term storage. Seed certification bodies should use vigour index I as a reliable measure to improve seed quality intended for planting.

Footnotes

Acknowledgements

The authors acknowledge the support of staff members of Sources Technology Multiplication and Seed Research Department and Melkassa Agricultural Research Center (MARC) administration for their contributions from proposal approval to trial management practices. Also all the reference materials used in this paper are duly acknowledged.

ORCID iD

Kedir Oshone Hussen

Ethical considerations

This research did not involve human participants, animals, or data derived from social media platform and copy of research done by scholars. I need to confirm that no scientific data has been generated or modified using AI.

Author contributions

Kedir Oshone Hussen: Conceptualization; Methodology; Data curative; Formal analysis; Investigation; Writing-original draft; Writing-review and editing; Validation; Software; and visualization. Karta Kaske Kalsa: Conceptualization; Methodology; Resource allocation; Data curative; Writing-review and editing; Supervision, and project administration.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research work was financially supported by Ethiopian Institute of Agricultural Research (EIAR).

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data Availability Statement

Dataset of research work on ‘Effects of seed Packaging, Storage Conditions, and Durations on Seed Quality of Open-Pollinated Maize (Zea mays L.) Varieties’ in Ethiopia (Original data) was attached with this revised manuscript.*

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