Evaluation of Pollination Potential in ‘Jinfeng’ Kiwifruit Seedling Male Plants Based on Floral Traits and Pollen Viability

Abstract

This study systematically assessed floral phenotypic traits, pollen viability, and ultrastructure in 120 male progeny of Actinidia chinensis ‘Jinfeng’. We documented floral features, measured pollen viability using Alexander staining and germination tests, and analyzed pollen morphology through scanning electron microscopy. Correlation analyses examined relationships between pollen viability and floral or pollen morphological traits. Results showed uniform qualitative floral traits but significant variation in quantitative traits. Pollen viability ranged widely (0.3–100%, CV = 43.60%) with consistent outcomes across assessment methods. Pollen grains were mainly prolate to perprolate with three germination furrows, polar axis length (P) ranged from 25.34 to 34.62 μm, equatorial axis length (E) ranged from 11.72 to 16.17 μm, and colpus length ranged from 20.6 to 30.58 μm. Viability was not correlated with quantitative floral traits or anther color but was significantly positively correlated with the polar/equatorial diameter ratio (P/E ratio, r = 0.622), indicating higher viability in perprolate pollen (P/E > 2.0). This study highlights significant genetic diversity in ‘Jinfeng’ male progeny and establishes a relationship between pollen morphology and viability in kiwifruit, providing a theoretical and practical basis for male selection and a foundation for pollen morphology research.

1. Introduction

Kiwifruit (Actinidia spp.) is a globally valued functional fruit known for its distinctive flavor, nutritional benefits, and commercial significance [1]. As a dioecious plant, the pollen quality of male kiwifruit plants directly impacts fruit set rate, seed count, and fruit size [2]. Therefore, breeding high-quality male plants has become a primary goal in kiwifruit breeding. In this context, systematic studies on floral organ traits, pollen viability, and pollen morphology are essential for screening kiwifruit germplasm resources, selecting pollinizer trees, and advancing efficient breeding programs. This focus is reflected in recent global palynological research. For example, Bocianowski et al. employed association mapping in Rubus to identify genetic markers for pollen traits, offering a modern tool for selection [3]. Negi et al. used LM and SEM to delineate Lauraceae species based on pollen morphology, providing a taxonomic framework [4]. Finally, Nazish et al. linked pollen viability and morphology to environmental adaptability in halophytes, highlighting their role in stress resilience [5]. These studies collectively underscore the value of integrating diverse palynological approaches into crop breeding and systematics. Current research on kiwifruit pollen has predominantly focused on aspects such as pollen viability, analysis of floral trait heritability, and morphological observation of pollen grains; however, it has not yet achieved a comprehensive, integrated analysis [6,7,8].

Floral traits such as pedicel length, number of sepals, sepal color, corolla diameter, arrangement of the petal base, waviness of the petal margin, adaxial color near the petal base, primary and secondary colors on the inner petal surface, and anther color are essential indicators for assessing genetic variation in male germplasm resources. These floral characteristics have been extensively studied in examinations of genetic diversity across various plants, including wheat [9], pear [10], kiwifruit [7,8], and strawberry [11]. Artificial pollination is a key technique for hybrid breeding and boosting crop yields [12]. Since pollen viability directly impacts the success of artificial pollination, evaluating it is crucial for selecting superior male plants [13]. The Alexander staining method, commonly used to assess pollen viability, relies on differential cytoplasmic metabolic activity—viable pollen stains red, while non-viable pollen appears blue. This method is straightforward and cost-effective [14]. However, its accuracy can be influenced by factors such as reagent concentration, staining duration, and the physiological status of the pollen, with a particular risk of false positives in osmotically sensitive species [14]. Conversely, the in vitro pollen germination method directly gauges pollen germination potential and offers high accuracy. However, it is time-consuming and highly dependent on the composition of the culture medium, making it less suitable for high-throughput screening [15]. Additionally, due to differences in pollen wall structure and content among species or varieties, the culture medium often needs optimization when using the pollen germination assay to evaluate viability.

Pollen morphology, a crucial tool in the taxonomic study of angiosperms, has been extensively utilized in research across various plant groups, including cherry [15], spinach [16], chrysanthemum [17], pear [18], and kiwifruit [19,20]. In pollen ultrastructure, the key metrics for assessing pollen morphology include exine ornamentation, polar axis length, equatorial axis length, germinal furrow characteristics, and the shape and size of grains. Correlation analysis of pollen viability and morphological traits in cherry showed that the in vitro pollen germination rate was positively related to the pollen length-to-width ratio (L/W, r = 0.640) and furrow width (r = 0.588) [15], indicating that ultrastructural features may impact pollen viability.

The ‘Jinfeng’ kiwifruit is a new, high-quality, late-ripening variety of Actinidia chinensis with yellow flesh. It is notable for its combination of strong adaptability, high stress resistance, high productivity, and excellent fruit quality [21]. In previous work, we developed an open-pollinated seedling progeny population of ‘Jinfeng’, most of which have reached the flowering stage. Field observations conducted over three consecutive years have demonstrated that this population of male seedlings exhibits high genetic diversity, characterized by traits such as a prolonged flowering period and abundant pollen production. It is therefore considered ideal breeding material for selecting superior male germplasm and developing complementary pollinizers for the ‘Jinfeng’ kiwifruit. In this study, we systematically examined and measured the floral traits and pollen viability of 120 ‘Jinfeng’ male seedlings. Additionally, scanning electron microscopy (SEM) was used to observe the pollen morphology of 40 selected individuals from this group. The aim was to clarify the genetic variation in floral traits, pollen viability, and pollen morphology, and to explore the mechanisms influencing the relationship between floral traits and pollen ultrastructure on pollen viability. The results will provide vital resources for the innovation of kiwifruit male germplasm and breeding strategies.

2. Materials and Methods

2.1. Plant Materials

The plant materials used in this study were selected from a progeny population of open-pollinated male plants of A. chinensis ‘Jinfeng’. This population was developed from fully ripe ‘Jinfeng’ fruits collected by our research team. After seed extraction, cleaning, sowing, and seedling cultivation, the plants were transplanted in February 2020 into the kiwifruit germplasm repository located in Fengxin County, Jiangxi Province, with a planting spacing of 0.5 m × 4 m. Conventional field management practices were applied throughout the cultivation period. A total of 120 vigorous, disease-free individuals were chosen as experimental materials (Orchard of Fengxin County Agriculture and Rural Affairs Bureau of Jiangxi Province, Yichun, China).

2.2. Sample Collection

During the full-bloom stage, a total of 30 fully opened flowers and 30 large-bud-stage flowers were collected each day between 9:00 and 11:00 AM. Randomly collect fully open flowers and buds from healthy branches on the upper part of the plant that are exposed to sunlight. The collected samples were immediately placed in zip-lock bags, transferred to ice-cooled containers, and quickly transported to the lab for further processing.

2.3. Floral Trait Recording and Measurement

For the 30 fully opened flowers collected, the following phenotypic traits were measured and recorded in accordance with the Guidelines for the Conduct of Tests for Distinctness, Uniformity, and Stability—Actinidia (Actinidia L.) (GB/T 19557.11-2022 [22]): pedicel length, number of sepals, sepal color, corolla diameter, arrangement of petal bases, degree of waviness at petal apices, adaxial color near the base of the inner petals, dominant color of the inner petals, secondary color of the inner petals, and anther color. Additionally, ten flowers at the large-bud stage were randomly selected to determine the number of anthers (n = 10). For each bud, the petals were removed, and all anthers were carefully dissected with forceps onto an A4 sheet for counting and recording. Pollen quantity was measured according to the method described by Shen et al. [23]. Briefly, 50 anthers were randomly placed in a 2 mL centrifuge tube (with three replicates per sample) and incubated at 28 °C for 24 h to allow full pollen release. Subsequently, 2 mL of a 200 g/L sodium hexametaphosphate solution was added, and the mixture was vortexed to form a homogeneous pollen suspension. A 400 μL aliquot of this suspension was transferred to a new 2 mL centrifuge tube, mixed with 1600 μL of the sodium hexametaphosphate solution, and the pollen grains were counted under a microscope (Nikon Corporation, Tokyo, Japan) using a hemocytometer (n = 10) (Shanghai Qiujing Experimental Instrument Co., Ltd., Shanghai, China).

2.4. Pollen Viability Measurement

Pollen viability was evaluated using Alexander’s staining method [24] and the in vitro germination method [25]. The process for Alexander’s staining involved placing a small amount of pollen on a glass slide, mixing it with two drops of staining solution, and incubating at a steady temperature of 35 °C for 15 min. After staining, the pollen was examined under a microscope. Viable pollen appeared purplish-red, while non-viable pollen did not stain. For each sample, six random fields of view were observed, with at least 200 grains counted in total. Pollen viability was calculated as (number of viable pollen grains/total pollen grains) × 100%. The procedure was repeated three times to ensure reliability and accuracy (n = 6).

A full factorial design was used for the in vitro pollen germination assay. Solid culture media with all combinations of sucrose concentrations (5%, 10%, 15%, 20%) and boric acid levels (0.1%, 0.15%, 0.2%) were prepared to find the optimal composition and assess any potential interaction between the factors. Sample 5-327, which contained abundant pollen and exhibited high viability as indicated by staining, was selected as the test material. An appropriate amount of pollen was evenly spread on the surface of the medium and incubated in darkness at 25 °C and 90% relative humidity for four hours. Germination was observed under a microscope, with a pollen tube length at least equal to the pollen diameter considered the indicator of successful germination. The same counting method used for the staining process was applied.

To further verify the consistency between the two methods, 20 extreme samples (high viability group ≥ 90%, low viability group ≤ 10%) were selected for comparative analysis.

2.5. Scanning Electron Microscopy (SEM) Observation and Morphological Analysis of Pollen

Pollen samples were carefully transferred onto conductive adhesive using lint-free paper, sputter-coated with gold for one minute using an ion sputter coater (Shanghai Vakia Coating Technology Co., Ltd., Shanghai, China), and subsequently observed with a Hitachi S-4800 (Hitachi Ltd., Japan, Tokyo) scanning electron microscope (SEM) operating at an acceleration voltage of 10.0 kV under high vacuum. Representative fields of view were selected to capture images at magnifications of 500×, 5000×, and 20,000×, respectively, to display pollen distribution, observe equatorial and polar views, and examine surface ornamentation details. From the 5000× images, six pollen grains were randomly chosen to measure five morphological traits: polar axis length (P), equatorial axis length (E), colpus length, colpus width, and the P/E ratio (n = 6). Pollen morphological characteristics were identified referencing the corresponding taxonomic keys [26,27,28,29].

2.6. Data Analysis

Data analysis was conducted using Microsoft Excel 2016. Correlation analysis was performed with SPSS 21.0 software, and graphs were generated with Origin 2024.

3. Results

3.1. Analysis of Floral Traits in ‘Jinfeng’ Seedling Male Plants

In accordance with the Guidelines for the Conduct of Tests for Distinctness, Uniformity, and Stability—Actinidia (Actinidia L.), a systematic characterization of floral organ traits was performed on 120 male progeny seedlings of ‘Jinfeng’. The results showed that pedicel length ranged from 1.87 to 6.18 cm, with a coefficient of variation (CV) of 24.36%, while corolla length varied from 2.85 to 5.11 cm, with a CV of 13.57%. Inflorescence architecture consisted of both dichasial and polychasial cymes, occurring at an approximate ratio of 1:1.1. All accessions had green sepals, typically numbering 5 to 7. The petal basal arrangement was mainly imbricate, with only one accession displaying a valvate arrangement and two accessions showing a contorted arrangement. The degree of undulation at the petal apex was generally minimal. The adaxial surface of petals consistently showed bicoloration, characterized by white as the primary color and green as the secondary hue. Pollen colors included orange-yellow and yellow, with an approximate ratio of 1:1.2. The number of anthers per flower ranged from 55 to 178 (CV = 28.92%), and pollen grain count per anther ranged from 3398 to 25,117 (CV = 45.38%) (Table S1 and

Table 1. Data for quantitative indices of floral traits and pollen viability.

Index	Pedicel Length/cm	Corolla Diameter/cm	Stamen Number	Pollen Quantity	Pollen Viability/%
Average	3.73	3.83	96.03	9654.48	72.78
SD	0.91	0.52	27.77	4381.56	31.60
Median	3.58	3.78	90.00	8273.50	90.09
Mode	2.89	3.07	79.00	6906.00	97.06
Min.	1.87	2.85	55.00	3398.00	0.33
Max.	6.18	5.11	178.00	25,117.00	100.00
CV/%	24.36	13.57	28.92	45.38	43.41
Range	4.31	2.26	123.00	21,719.00	99.67

Note: SD: Standard Deviation; CV: Coefficient of Variation.

). According to the range analysis, the maximum values of the five male flower traits were several times greater than their minimum values. The germination rate showed the most significant difference, being 303.03 times greater, followed by pollen quantity at 7.39 times, and the least significant difference was observed in corolla diameter at 1.79 times (Table 1). In summary, all five male flower traits of the Jinfeng kiwifruit male plants exhibited extensive variation, with pollen germination rate showing the most tremendous variability.

3.2. Pollen Viability Evaluation of ‘Jinfeng’ Seedling Male Plants

Alexander staining revealed that the pollen viability of ‘Jinfeng’ seedling-derived male plants ranged from 0.3% to 100%, with a coefficient of variation of 43.60%. Among these, 50% of the male plants exhibited pollen viability exceeding 90% (Table 1, Figure 1A,C). For the in vitro pollen germination assay, various combinations of sucrose and boric acid concentrations were initially tested to optimize the solid medium formulation. The results showed that the highest pollen germination rate was achieved with 0.15% boric acid and 10% sucrose (Figure 2). Therefore, the final medium composition was determined as 10% sucrose, 0.15% boric acid, and 0.8% agar. Using this optimized medium, an in vitro pollen germination test was conducted on 20 samples with significantly different viability levels, as assessed by the staining method (Table 1 and

Table 2. Pollen viability of 20 male plants from ‘Jinfeng’ kiwifruit seedlings.

Number	Staining Method	Pollen Germination Method	Number	Staining Method	Pollen Germination Method
7-601-4	1.000 ± 0.000	0.759 ± 0.049	1-54	0.155 ± 0.043	0.000 ± 0.000
5-327	1.000 ± 0.000	0.841 ± 0.062	2-96	0.131 ± 0.039	0.007 ± 0.012
7-601	0.997 ± 0.004	0.774 ± 0.102	5-321	0.116 ± 0.028	0.000 ± 0.000
3-156	0.995 ± 0.007	0.720 ± 0.116	7-600-1	0.105 ± 0.103	0.000 ± 0.000
11-510	0.994 ± 0.006	0.678 ± 0.060	1-51	0.068 ± 0.019	0.000 ± 0.000
4-290-1	0.993 ± 0.003	0.716 ± 0.079	11-512	0.050 ± 0.030	0.000 ± 0.000
5-311	0.992 ± 0.008	0.610 ± 0.096	1-81	0.037 ± 0.038	0.000 ± 0.000
2-132-1	0.992 ± 0.006	0.744 ± 0.103	1-8	0.009 ± 0.001	0.000 ± 0.000
1-56	0.991 ± 0.008	0.529 ± 0.130	1-74	0.005 ± 0.004	0.000 ± 0.000
2-136	0.991 ± 0.016	0.614 ± 0.029	2-120	0.003 ± 0.006	0.000 ± 0.000

). The viability values from the germination assay were consistently lower than those from the staining process, and pollen with low viability failed to germinate (Figure 1B,D). A strong positive correlation was observed between the results of the two methods (r = 0.982, p < 0.01), confirming the reliability and consistency of the findings.

3.3. Scanning Electron Microscopy of Pollen from ‘Jinfeng’ Seedling Male Plants

Based on the pollen viability assessment results, 40 pollen samples were randomly chosen in proportion to different viability levels for SEM observation. The findings showed that pollen from ‘Jinfeng’ seedling-derived male plants was mostly prolate or nearly perprolate, with a tri-lobed circular polar view. All pollen grains had three germination furrows, evenly spaced along the polar axis (Figure 3). The pollen grains were generally small, with the following measurements: polar axis length (P) ranged from 25.34 to 34.62 μm, with a CV of 7.54%; equatorial axis length (E) ranged from 11.72 to 16.17 μm, with a CV of 8.58%; colpus length ranged from 20.6 to 30.58 μm, accounting for 80–90% of the polar axis length (only one sample showed 77%), CV = 9.35%; colpus width ranged from 6.56 to 9.76 μm, CV = 9.28%; and P/E ratio ranged from 1.93 to 2.28, CV = 4.85% (Table S2 and

Table 3. Data for quantitative indices of Pollen morphological indicators.

Index	Polar Axis Length/μm	Equatorial Axis Length/μm	Colpus Length/μm	Colpus Width/μm	P/E	Floral Vitality/%
Average	28.45	13.51	24.34	7.94	2.11	71.45
SD	2.12	1.14	2.25	0.73	0.10	33.60
Median	27.64	13.29	23.74	7.89	2.11	90.63
Mode	28.14	12.34	22.75	7.48	2.14	100.00
Min.	25.34	11.72	20.86	6.56	1.71	3.72
Max.	34.62	16.17	30.58	9.76	2.29	100.00
CV/%	0.07	0.08	0.09	0.09	0.05	0.47
Range	9.28	4.45	9.72	3.20	0.58	96.28

Note: SD: Standard Deviation; CV: Coefficient of Variation.

). Most male plant pollen grains were nearly perprolate (P/E > 2.0), with only three samples (1-8, 1-81, 6-355) classified as perprolate. The pollen exine ornamentation was primarily regulated, with a relatively smooth surface composed of irregular, band-like ridges, resulting in a finely undulating outline (Figure 3E,F). All germination furrows extended along the polar axis toward both poles but did not fuse at the tips to form a syncolpus, maintaining equal spacing throughout. In the equatorial view, one or two spindle-shaped germination furrows were visible, while three sunken germination furrows could be seen in the polar view (Figure 3D).

3.4. Correlation Analysis

We analyzed the relationship between pollen viability and floral traits based on an average of 120 individuals and found significant negative associations with several floral traits. Specifically, pollen viability showed a significant negative correlation with stamen number (r = −0.418, p < 0.01) (Figure 4A). A moderately significant negative correlation was noted between pollen viability and corolla diameter (r = −0.307, p < 0.01), while a weaker but still significant negative correlation was observed with pedicel length (r = −0.232, p < 0.05). Additionally, pollen viability showed a very weak and non-significant positive correlation with pollen quantity (r = 0.109) (Figure 4A).

To investigate the relationship between pollen vitality and morphology, a correlation analysis was performed using the average of 120 individual pollen grains. It indicated a strong, significant positive correlation between pollen viability and the polar/equatorial diameter ratio (P/E) (r = 0.622, p < 0.01). This suggests that pollen viability increases as the pollen shape becomes more perprolate. Conversely, no significant relationships were found between pollen viability and other morphological indicators, such as polar axis length, equatorial axis length, colpus length, and colpus ridge width (Figure 4B), indicating that pollen viability is independent of these specific morphological traits.

3.5. Principal Component Analysis of All Male Floral Traits

To explore the main contributing components of the male flower traits in 120 Jinfeng kiwifruit seedling offspring, a principal component analysis (PCA) was conducted. Since pollen quantity showed no significant correlation with other indicators in the PCA, it was excluded from the factor analysis to achieve a cumulative contribution rate of over 80%, meeting the desired standard. The eigenvector values, eigenvalues, contribution rates, and cumulative contribution rates for the three principal components are shown in

Table 4. Principal component analysis.

Item	Principal Component
	PC1	PC2	PC3
Pedicel length	−0.06	0.48	0.17
Corolla diameter	0.04	0.40	0.07
Stamen number	−0.04	0.27	−0.10
Polar axis length	0.28	0.06	0.14
Equatorial axis length	0.25	−0.04	−0.20
Colpus length	0.27	0.05	0.20
Colpus width	0.27	−0.15	−0.15
P/E	−0.02	0.15	0.53
Pollen vitality	0.07	−0.12	0.35
Eigenvalues	3.69	2.49	1.39
Contribution rates/%	38.39	24.12	21.79
Cumulative contribution rates/%	38.39	62.50	84.29

. The eigenvalue of the first principal component is 3.69, with a contribution rate of 38.39%. The eigenvector values for polar axis length, colpus length, and colpus width are relatively high, at 0.28, 0.27, and 0.27, respectively. This indicates that pollen grain size dimensions predominantly determine the male floral traits of kiwifruit. The formulas for the principal component factor scores and the comprehensive evaluation score are as follows:

F₁ = −0.06X₁ + 0.04X₂ − 0.04X₃ + 0.28X₄ + 0.25X₅ + 0.27X₆ + 0.27X₇ − 0.02X₈ + 0.07X₉

F₂ = 0.48X₁ + 0.40X₂ + 0.27X₃ + 0.06X₄ − 0.04X₅ + 0.05X₆ − 0.15X₇ + 0.15X₈ − 0.12X₉

F₃ = 0.17X₁ + 0.07X₂ − 0.10X₃ + 0.14X₄ − 0.20X₅ + 0.20X₆ − 0.15X₇ + 0.53X₈ + 0.35X₉

F = 0.46F₁ + 0.29F₂ + 0.26F₃

The top four samples with the highest comprehensive evaluation scores were 5-327, 1-13, 5-322, and 5-163-1 (

Table 5. Comprehensive evaluation score of excellent male plant lines of Jinfeng seedlings.

Number	Comprehensive Evaluation Score	Pollen Vitality/%
5-327	1.20	100
1-13	1.19	78.62
5-322	1.18	27.4
5-163-1	1.05	34.4

). These results indicate that samples 5-327, 1-13, 5-322, and 5-163-1 exhibited the best overall performance in terms of flower traits. When combined with pollen viability indicators, 5-327 and 1-13 were identified as high-quality germplasms suitable for breeding.

4. Discussion

This study systematically examined the floral morphological traits, pollen viability, and pollen microstructure of the male offspring of Actinidia chinensis ‘Jinfeng’. The findings highlight key reproductive biological features of this population and provide valuable insights for conserving genetic diversity and utilizing kiwifruit germplasm in breeding. Observations of 120 male offspring of ‘Jinfeng’ revealed consistent traits, including inflorescence structure, petal number, sepal color and number, petal color, and anther color. In contrast, quantitative traits such as pedicel length, corolla diameter, the number of anthers per flower, and pollen quantity per anther exhibited wide variation, consistent with previous reports by Liang et al. [7] and Zhong et al. [8].

The pollen viability of 120 male progeny of ‘Jinfeng’ was evaluated, showing considerable variation among individuals, with values ranging from 0.3% to 100% and a CV as high as 43.60%. The population included both high-viability accessions (e.g., 5-327, 7-601-4) and low-viability accessions (e.g., 1-74, 2-120) (Table 3). This high variability in pollen viability, along with the notable variation in quantitative floral traits such as pollen quantity per anther (CV = 45.57%), indicates significant genetic diversity within this population. For assessment methods, both the in vitro pollen germination assay and Alexander staining were used. The staining method produced slightly higher viability values compared to the germination assay. Nonetheless, a highly significant positive correlation was observed between the two methods, consistent with the findings of Sharma et al. [30].

SEM observation of 40 male accessions revealed the following pollen morphological features: polar axis length ranging from 25.34 to 34.62 μm, equatorial axis length from 11.72 to 16.17 μm, colpus length from 20.86 to 30.58 μm, colpus width from 6.56 to 9.76 μm, and P/E ratio from 1.93 to 2.28. All these traits showed relatively low coefficients of variation. Most pollen grains were perprolate (P/E > 2.0), with only three accessions being prolate. The pollen exine ornamentation was mainly undulate and relatively smooth, and all grains had three equally spaced germination furrows. These morphological features align with reports by He et al. [19], Qi et al. [20], and Zhong et al. [31]. Qi et al. [20] proposed that pollen morphology and size tend to be relatively conserved within the same species and under similar environmental conditions, a view supported by this study.

As reported by Habibi et al. [32] and Hebda and Chinnappa [33], germination furrow length shows a strong positive correlation with polar axis length, with the furrow length accounting for approximately 80–90% of the polar distance—a finding confirmed by this study. In this research, pollen viability was significantly positively linked to the P/E ratio (r = 0.622), indicating that pollen grains with a more prolate shape (P/E > 2.0) generally have higher viability. Similarly, Rakonjac et al. [15] also observed a positive correlation between pollen viability and the P/E ratio in different cherry cultivars (r = 0.640), supporting the conclusion here and suggesting a possible common morpho-functional relationship across plant species. The mechanism behind this may relate to the geometric advantages of the prolate shape. From a hydration kinetics perspective, prolate pollen grains exhibit optimized surface-area-to-volume ratios that accelerate water uptake during critical rehydration phases. The elongated morphology also provides structural advantages for exposing the intine and allocating nutrients along the polar axis, contributing to more efficient pollen tube growth. These results suggest that in breeding or cultivation, pollen morphology, especially the P/E ratio, could serve as a quick and simple morphological marker for assessing pollen viability. Notably, there was no significant correlation between germination furrow ridge width and pollen viability in this study, contrasting with previous findings in cherry [15]. First, species-specific genetic regulation may lead to differential expression of germination furrow ridge width across plant taxa. Association mapping in Rubus has demonstrated that pollen morphological traits are governed by specific genetic markers [3]. At the same time, the high consistency of exine ornamentation observed in kiwifruit seedling male progeny suggests stricter genetic constraints on germination furrow development, resulting in low individual variation and consequently weakening its correlation with viability. Furthermore, larger pollen grains in cherry (48.6–54.5 μm) likely rely more heavily on the mechanical support function provided by germination furrow ridges, whereas kiwifruit prioritizes optimization of overall hydration efficiency. These findings underscore the importance of prioritizing core geometric traits, such as the P/E ratio, while concurrently accounting for species-specific genetic backgrounds and evolutionary adaptation strategies.

Multiple studies have demonstrated that environmental factors directly influence pollen viability by regulating physiological processes during pollen development. Research on halophytes revealed a positive correlation between exine thickening (e.g., an exine thickness of 2.95 μm in Vachellia nilotica) and high pollen viability (68.85–90.16%) [5]. This structural characteristic helps reduce water loss and maintain osmotic balance. In this study, the significant correlation between the P/E ratio and viability (r = 0.622) may similarly reflect the optimization of hydration efficiency through pollen geometric morphology. This trait is particularly critical under environmental stress conditions.

Principal component analysis in this study revealed that the first component exhibits the highest eigenvector value for polar axis length, with a contribution rate of 38.39%, indicating that polar axis length carries significant weight in evaluating male plants. This finding aligns with Nazish’s principal component analysis results on pollen morphological traits in halophytes [5]. Consequently, the top five superior lines based on comprehensive evaluation scores were selected: 5-327, 1-13, 5-322, and 5-163-1. Among these, lines 5-327 and 1-13 exhibit pollen viability exceeding 70%.

5. Conclusions

In summary, this study systematically examined the genetic diversity and conservation of floral phenotypic traits, pollen viability, and pollen micromorphology in male progeny of ‘Jinfeng’. To our knowledge, this is the first report of a significant correlation between the P/E ratio—a key pollen morphological index—and pollen viability in the genus Actinidia, thereby providing a theoretical foundation and a practical measure for the efficient selection of superior pollinizers. Additionally, 60 accessions with high pollen viability were identified, offering valuable breeding materials and theoretical support for future kiwifruit breeding efforts. Subsequent research will focus on their pollen compatibility, fruit set rate following pollination, fruit quality, and yield characteristics, ultimately aiming to select male cultivars with superior traits suitable for production.