Evaluation of Nutritional and Popping Quality of Popcorn Genotypes Under Rainfed Conditions ^†

Abstract

Popcorn (Zea mays everta) is a special type of flint maize that boasts several unique popping characteristics highly valued worldwide. Water-limiting conditions strongly influence the major popcorn quality attributes: expansion volume, popability, and nutritional composition. The objectives of this study were to identify rainfed popcorn genotypes with superior popping quality, nutritional quality, and agronomic performance. Seven diverse popcorn genotypes, including a check cultivar, were evaluated for two consecutive years (2023–2024) using a randomized complete block design with three replications at the university research farm, PMAS-AAUR. Significant genetic variations were observed across all morphological, physiological, and quality-related traits. Among the evaluated materials, Pop-2 consistently exhibited outstanding performance in key agronomic and physiological attributes as well as in popping quality, while Pop-5 and Pop-3 also showed promising potential. Overall, Pop-2, Pop-5, and Pop-3 were identified as the most suitable genotypes for cultivation and are recommended as candidates for future breeding programs targeting improved popcorn performance under rainfed conditions.

1. Introduction

Maize (Zea mays L.) is a major cereal of global importance and belongs to the family Poaceae, possessing 20 chromosomes, a 2.3 gigabase genome, and approximately 32,000 genes [1]. With a yearly yield of 1.2 billion tons from 197 million hectares, it is the most important cereal crop in the world. The majority of the 8.24 million tons of maize produced on 1.44 million hectares of land in Pakistan are used as food, seed, wet milling, and chicken feed [2].

A unique kind of flint maize, popcorn (Zea mays everta) is consumed as a healthy snack and has substantial commercial value all over the world [3,4]. Its small, firm kernels that are enhanced with thick starch are responsible for its special bursting power [5]. Protein and oil content are important factors that determine nutritional quality [6], while expansion volume (EV) and popability are the main indications of popping performance [7,8]. The main objectives of breeding and production for popcorn growers are the increase in EV, popability, and a decrease in unpopped kernels [9]. Due to its complex nutritional profile, comprising essential proteins, lipids, carbs, minerals, and vitamins [10], recognized as a healthy whole-grain snack food [11].

Popcorn also contributes to food security in underdeveloped countries [12]. In spite of the importance, popcorn production in areas under rainfed conditions is unstable yet [13]. Drought stress drastically alters the biochemical composition of kernels, in particular, protein and oil content, which results in decreases in expansion volume and popping % [14,15]. In turn, moisture deficiency negatively affects kernel hardness and moisture dynamics, both important for good popping [16]. Thus, for sustaining good popping quality under drought conditions, it is necessary to ensure appropriate moisture in the soil during grain filling [17].

In light of these difficulties, the current study, “Evaluation of Nutritional and Popping Quality of Popcorn Genotypes under Rainfed Conditions,” was carried out to evaluate how well various popcorn genotypes performed in terms of popping characteristics, nutritional qualities, and agronomic suitability under rainfed conditions. In order to increase popcorn quality in water-limited regions, the results are intended to identify viable genotypes for cultivation and future breeding initiatives.

2. Materials and Methods

The field experiment was conducted at the University Research Farm, Chakwal Road, Rawalpindi (33.1167° N, 73.0147° E) and associated laboratory analyses were performed at the Department of Plant Breeding and Genetics, PMAS-AAUR. The study was carried out during the 2023 and 2024 popcorn growing seasons. Meteorological data for the two cropping seasons (April–August, 2023–2024) were obtained from the Agromet Section of the University Research Farm (33.078° N, 72.833° E); monthly mean maximum and minimum temperatures (°C), total monthly rainfall (mm), and average relative humidity (%) were recorded for the crop period (Figure 1).

Figure 1. Meteorological data for crop growing seasons (April–August, 2023–2024) University Research Farm Chakwal Road, Rawalpindi.

Seven diverse popcorn genotypes were evaluated: Pop-1, Pop-2, Pop-3, Pop-4, Pop-5, Pop-6 and the check cultivar Pirsabak. These materials were obtained from Cereal Crops Research Institute (CCRI) Pirsabak-Nowshera, Agricultural Research Institute (ARI) Swat-Mingora and Agricultural Research Station (ARS) Sarai Naurang (Table 1).

Table 1. List of popcorn genotypes.

S. No.	Code	Source
1	Pop-1	ARI Swat-Mingora
2	Pop-2	CCRI, Pirsabak-Nowshera
3	Pop-3	CCRI, Pirsabak-Nowshera
4	Pop-4	ARS, Sarai-Naurang
5	Pop-5	ARI, Swat-Mingora
6	Pop-6	ARS, Sarai-Naurang
7	Pirsabak (Check)	CCRI, Pirsabak-Nowshera

The experiment was laid out in a randomized complete block design (RCBD) with three replications. Each genotype was sown in two rows of 3.0 m length. Inter-row spacing was 75 cm and intra-row spacing was 25 cm. Standard agronomic practices were followed uniformly for all replications from sowing to harvest.

Five plants were selected at random for each genotype in each replication for detailed plant level measurements. Data were collected on morphological, physiological, popping quality and nutritional parameters.

Morphological characteristics such as days to 50% tasseling, days to 50% silking, plant height, kernels per row, kernel rows per ear and grain yield per plant were recorded following standard guidelines. Measurements were made on the five randomly selected plants for each genotype in each replication [18].

Physiological characters, like Chlorophyll content was measured as SPAD units using a portable chlorophyll meter following standard practice [13]. Leaf area index (LAI) was estimated by dividing leaf area (m²) by the ground area (m²), and cell membrane thermostability was measured as per the established standard procedures [11]. Expansion volume was calculated by dividing the difference in the volume of the kernels before and after the popping process by the original weight of the sample [2]. All popped volumes were measured immediately after popping to avoid volume loss.

The protein content was calculated by the Kjeldahl method and expressed on a dry weight basis. According to [19], the crude oil content was determined by Soxhlet extraction using petroleum ether. Laboratory analyses for each replication sample were carried out in triplicate, and mean values were given.

Statistical Analysis

The recorded data were subjected to the analysis of variance using statistical software (statistics 8.1) to find out whether there was any significant difference between the genotypes of popcorn. Using the least significant differences test at a probability level of 5% (0.05), mean differences between popcorn genotypes for various nutritional and popping quality parameters were ascertained.

3. Results

Various morphological, physiological, popping quality, and nutritional parameters were evaluated in seven genotypes of popcorn, all of which showed a great genetic variation (Table 2, Table 3, Table 4 and Table 5). This diversity indicates strong potential for improvement and selection. Mean values and ranges for studied traits of various popcorn genotypes, along with best performing genotypes against each trait were presented in (Figure 2), while (Figure 3) showed heatmap of agronomic and quality traits of various studied popcorn genotypes.

Table 2. Mean square values for morphological traits of various studied popcorn genotypes.

	Source of Variations with Degree of Freedom
Traits	Replication (2)	Genotypes (6)	Error (12)	CV (%)
Days to 50% germination	1	5.63 *	0.4	7.91
Days to 50% tasseling	4.9	19.43 **	2.24	2.60
Days to 50% silking	2.3	35.54 *	0.44	1.07
Plant height (cm)	94.9	193.89 **	55.96	4.49
No. of kernel rows ear−1	0.01	4.60 **	1.27	7.21
No. of kernels row−1	2.3	14.32 **	1.72	4.08
Grain yield plant−1 (g)	142.1	1527.10 **	356.9	12.28

* Significant, ** Highly Significant.

Table 3. Mean square values for physiological, popping and nutritional quality traits of various studied popcorn genotypes.

	Source of Variations with Degree of Freedom
Traits	Replication (2)	Genotypes (6)	Error (12)	CV (%)
Chlorophyll content (%)	2.8	67.7 **	3.2	4.62
Leaf area index (LAI)	0.02	0.57 **	0.03	5.8
Cell membrane thermostability	44.3	180.97 **	3.4	2.36
Kernel size	0.01	0.04 *	0.001	6.39
Popability (%)	1.2	190.28 *	2.20	1.75
Expansion volume (cm3 g−1)	6	41.54 **	1.52	7.94
Protein content (%)	3.75	58.84 **	3.75	20.9
Kernel oil content (%)	0.3	3.96 **	0.04	4.17

* Significant, ** Highly Significant.

Table 4. Mean and ranges of morphological, physiological, popping and nutritional quality traits of various studied popcorn genotypes.

Traits	Range	Mean	Best Genotypes
Days to 50% germination	7–11	8.43	Pop-5, Pop-6
Days to 50% tasseling	53–60.54	57.52	Pop-5, Pop-2
Days to 50% silking	56.34–67.66	62.19	Pop-2, Pop-7
Plant height (cm)	153–176.3	166.67	Pop-1, Pop-7
No. of kernel rows ear−1	14–18	15.61	Pop-2, Pop-3
No. of kernels row−1	29.66–36	32.19	Pop-2, Pop-1
Grain yield plant−1 (g)	18.67–189	153.81	Pop-2, Pop-7
Chlorophyll content (%)	30.24–45.70	38.85	Pop-2, Pop-1
Leaf area index (LAI)	2.64–3.87	3.10	Pop-2, Pop-4
Cell membrane thermostability	63.67–89.33	78.76	Pop-2, Pop-5
Kernel size	0.23–0.62	0.41	Pop-2, Pop-1
Popability (%)	74.36–95.57	84.71	Pop-3, Pop-2
Expansion volume (cm3 g−1)	10.63–22.03	15.56	Pop-2, Pop-3
Protein content (%)	7.26–11.72	9.26	Pop-3, Pop-7
Kernel oil content (%)	4.50–7.80	5.24	Pop-6, Pop-3

Table 5. Heritability and variance components of various popcorn genotypes.

Traits	Vg	Ve	Vp	h2
Days to 50% germination	1.73	0.44	2.17	79.725
Days to 50% tasseling	5.73	2.2381	7.97	71.912
Days to 50% silking	11.70	0.4444	12.14	96.340
Plant height (cm)	45.98	55.96	101.94	45.103
No. of kernel rows ear−1	1.11	1.26984	2.38	46.667
No. of kernels row−1	4.20	1.7222	5.92	70.912
Grain yield plant−1 (g)	390.07	356.88	746.95	52.222
Chlorophyll content (%)	21.51	3.2284	24.74	86.949
Leaf area index (LAI)	0.18	0.03278	0.21	84.600
Cell membrane thermostability	59.18	3.444	62.62	94.500
Kernel size	0.02	0.0007	0.02	95.702
Popability (%)	62.69	2.201	64.89	96.608
Expansion volume (cm3 g−1)	13.34	1.5252	14.87	89.741
Protein content (%)	18.36	3.76	22.12	83
Kernel oil content (%)	1.30	0.04798	1.35	96.453

Figure 2. Graph representing mean values and ranges for studied traits of various popcorn genotypes, along with best performing genotypes against each trait.

Figure 3. Heatmap of agronomic and quality traits of various studied popcorn genotypes.

3.1. Morphological Traits

Days to 50% germination, tasseling, silking, plant height, kernel rows per ear, kernels per row, and grain production per plant showed significant variations. Pop-2 consistently performed better over Pop-5 and Pop-6 for yield attributes like kernel rows, kernels per row, and grain production per plant, whereas the latter two predominantly exhibited early phenology. This trend indicates that Pop-2 combines the advantage of higher yield potential with early flowering—an important attribute under rainfed conditions. These traits are reliable for selection due to their moderate to high estimates of heritability (Table 5), which indicate that the variation observed was predominantly genetic.

3.2. Physiological Traits

There were also significant differences among the genotypes for cell membrane thermostability, LAI, and chlorophyll content. Among them, Pop-2 performed best regarding all three physiological traits. Strong physiological expression of Pop-2 indicates increased membrane stability and photosynthetic efficiency in this population, which is associated with tolerance in water-limited environments. The possibility of improving such characteristics through breeding is further supported by high heritability values.

3.3. Popping Quality Traits

Pop-ability, expansion volume, and kernel size showed variation with high significance. Most importantly, Pop-2 and Pop-3 gave better popping performance, particularly for expansion volume—a key quality trait in popcorn. Because popping characteristics are highly heritable and linked closely to kernel structure, consistent performance by these genotypes suggests genetic control rather than environmental effect.

3.4. Nutritional Traits

In a similar way, great variability was found among genotypes in protein and oil contents. While Pop-3 presented the highest protein content, Pop-6 furnished the highest oil content. Such differences reinforce the possibility of identifying genotypes that would combine high popping performance with nutritional improvements.

4. Discussion

From the significant variability recorded in all the parameters studied, it is obvious that the studied popcorn germplasm possesses substantial genetic diversity that would be conducive to effective selection in breeding programs. The heritability estimates for most of the variables, especially those related to phenology, popping quality, and stress physiology, were relatively high, indicating that these qualities are largely controlled by genetic influences rather than environmental changes. In fact, [16,17,20] reported similar results on phenological and yield attributes in maize and popcorn germplasms.

Early maturity of Pop-5 and Pop-6 may be attributed to the fact that they have spent more effective growth cycles in rainfed environments, which corroborates research [17] that early emergence and reproductive timing improve adaptation under moisture stress. Pop-2 always outperformed other genotypes regarding yield-related and physiological variables owing to higher photosynthetic activity and structural characteristics such as more kernel rows and a higher LAI. Previous studies [9,11] have also pointed out that genotypes with higher membrane stability and chlorophyll content tend to function better under environmental stress.

The superb popping characteristics of Pop-2 and Pop-3, particularly for expansion volume, underpin kernel structure and moisture dynamics as critical factors for popping quality. The studies [21,22,23] also reported that the genotypes with big, uniformly shaped kernels and uniform moisture imbibition have great expansion volumes. Improvement in the quality of popcorns could be achieved without proximate composition penalty, since Pop-3 and Pop-6 showed nutritional advantages.

Overall, the results presented highlight the fact that Pop-2, Pop-3, and Pop-5 possess better trait combinations suitable for rainfed popcorn production. Their performance based on agronomic, physiological, and quality parameters showed that they hold great potential for use as parents in breeding programs with the aim of improving popping quality, stress tolerance, and grain yield.

5. Conclusions

This study reports that there was significant genetic variation among the seven popcorn genotypes evaluated under rainfed conditions. Pop-2, Pop-5, and Pop-3 consistently performed well in most of the major agronomic, physiological, nutritional, and popping-quality traits. These could be used for production in rainfed conditions because of their excellent expansion volume, high pop ability, and stability under limited water conditions. Furthermore, these genotypes are recommended as ideal parent material for future breeding efforts in further improving the quality and drought tolerance of popcorn.