Dose-dependent effects of gamma irradiation on growth and reproductive traits of strawberry

Abstract

Background

Radiosensitivity tests must be performed to determine the ideal doses before using gamma irradiation. This study investigated the effects of varying doses of gamma radiation (0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 Gy) on the growth and reproductive development of strawberry plants.

Results

Gamma irradiation exhibited a clear dose-dependent response in strawberry plants, with 30 Gy producing the most favorable responses for several vegetative and reproductive traits. At 30 Gy, plants showed the highest leaf area, flower number (16.66 flowers plant⁻¹), root length (20.66 cm), and leaf fresh and dry weights (2.69 and 0.83 g, respectively). In contrast, doses ≥ 60 Gy markedly reduced survival and most growth and reproductive parameters, with severe effects at 80–100 Gy. The estimated LD25, LD50, and LD75 values were 23.6, 51.7, and 79.8 Gy, respectively, providing a quantitative radiosensitivity profile for dose selection in subsequent gamma-induced mutation-breeding experiments.

Conclusions

These results demonstrate that the moderate gamma-ray dose (30 Gy) produced the most favorable growth, root development, and flowering responses in strawberry, indicating a possible hormetic effect. Doses above 50 Gy markedly reduced survival and growth, identifying them as potential candidate doses for subsequent mutation-breeding studies, pending confirmation of heritable genetic variation.

Introduction

Fruits are essential components of a balanced diet and offer numerous health benefits. With increased awareness of these advantages, more people are incorporating fruits and vegetables into their daily diets. According to the FAO and WHO, consuming a minimum of 400 g of fruits and vegetables per person per day is recommended for the prevention of chronic diseases and micronutrient deficiencies [1]. Strawberries, in particular, are rich in natural antioxidants, such as minerals, vitamin C, folate, and phenolic compounds, enhancing their nutritional value [2]. The popularity of strawberries among consumers worldwide is well established [3].

Creating new strawberry germplasm through various breeding methods is crucial to improve cultivars with high yield capacity, precocity, low percentage of second-class fruits, good shelf life, and exceptional organoleptic fruit quality (e.g., flavor, shape, firmness, color, etc.). To achieve these goals, numerous breeding programs have been established globally [4]. In addition to traditional breeding techniques, plant breeders have turned to cutting-edge methods like genetic engineering and mutation breeding to meet evolving challenges. While traditional breeding efforts have encountered genetic bottlenecks, mutation methods offer the potential to introduce desired traits that are either absent from nature or lost through evolution [5, 6].

Mutation breeding accelerates the emergence of desirable traits by inducing mutations with various tools instead of relying solely on natural mutations, which may take years to occur. Selecting the appropriate mutagen and developing methods to identify mutants are critical of mutation breeding [7]. Nuclear techniques play a crucial role in increasing the frequency and occurrence of useful mutations in plant mutation breeding. Mutation breeding has contributed to the development of over 3000 crop varieties with resistance to pests and other desirable agronomic traits across 50 countries worldwide [8, 9]. Physical mutagens, particularly gamma irradiation, have proven [8] effective in inducing beneficial traits in crop breeding. Gamma irradiation alters cellular composition, leading to artificial mutations that modify plant growth physiologically, biochemically, and agronomically. Consequently, gamma irradiation serves as a potent tool for inducing genetic changes and enhancing crops by generating beneficial mutants [10–12]. Gamma irradiation has been highly effective in inducing genetic variations in many fruit trees, including strawberries [13], guava [14], citrus [15], mango [16], grape [17], papaya [18], pear [19], and kiwifruit [20]. However, the effects of gamma rays on plant growth characteristics depend on various factors, including plant species, genus, growth stage, radiation source, dose level, and dose rate [21]. Identifying the optimal mutagen dose is crucial for successful mutation induction, as it maximizes mutation frequency while minimizing unintended damage. Gamma radiation, due to its ability to penetrate target tissues deeply with minimal damage, is considered the most effective electromagnetic radiation for crop improvement [22]. Although gamma-induced variation and radiosensitivity have been investigated in strawberry, available studies have largely focused on specific cultivars, propagation systems, or a limited set of response traits. The present study extends this knowledge by systematically evaluating a broad gamma-dose range (0–100 Gy) in Camarosa strawberry runners under controlled greenhouse conditions and by integrating vegetative, root, biomass, flowering, and fruit responses with multivariate analyses. This approach enables identification of dose-dependent response zones and distinguishes low-dose stimulatory responses from high-dose growth inhibition. Importantly, the study provides a cultivar and propagation-specific radiosensitivity baseline that can guide the selection of irradiation doses for subsequent mutation-breeding experiments. Rather than considering the dose producing maximum growth as a universal mutagenic optimum, the present work identifies biologically informative dose ranges that can be used to design subsequent mutant populations and selection strategies.

Materials and methods

Plant material

Commercially cultivated runners of strawberry cv. ‘Camarosa’ (Fragaria × ananassa Duch.) were used in this study. The plant material was obtained from a commercial greenhouse in Alborz Province, Iran, owned by co-author Masoud Shahmoradi. Permission for the collection and experimental use of the plant material was granted by the greenhouse owner. The identity of the plant material as cv. ‘Camarosa’ was based on the cultivar information associated with the commercially cultivated plants. No wild, endangered, or protected plant species were collected. Because the experimental material consisted exclusively of a commercially cultivated and well-established strawberry cultivar obtained from a commercial production system, no independent taxonomic identification or voucher specimen deposition was undertaken. Strawberry runners were sterilized by immersion in a 4000 ppm benomyl solution for 5 min before being wrapped in wet paper.

Gamma irradiation, and cultivation conditions

Eleven groups of runners were prepared. The first group served as the control, while the remaining samples were treated with gamma irradiation doses of 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 Gy at the Nuclear Science and Technology Research Institute in Karaj, Iran. The samples were irradiated using a Cobalt-60 gamma source with a total activity of approximately 290 Ci and a dose rate of approximately 0.049 Gy/s. For each treatment, a total of 60 runners were used, divided into three biological replicates (each consisting of 20 runners). The runners were arranged within the irradiation chamber according to the standard irradiation configuration of the facility, with samples positioned at central and peripheral locations relative to the radiation source to facilitate assessment of dose uniformity. The irradiation chamber was cylindrical, with an internal radius of 6.5 cm and a height of 23 cm. Strawberry runners and dosimeters were positioned within the chamber according to the standard irradiation configuration of the facility. Dosimetry was performed using Fricke dosimeters. Then dosimeters were distributed at representative central and peripheral positions within the irradiation chamber to assess the delivered absorbed dose and its spatial uniformity. The irradiation doses reported in this study correspond to the absorbed doses determined using the Fricke dosimetry system.

Both control and gamma-treated samples were planted in 10-liter plastic bags containing cocopeat and perlite (2:1). Light irrigation was immediately administered after planting, followed by subsequent irrigation based on the moisture levels. Individual plant growth occurred under controlled conditions with daytime temperatures maintained at 25 °C and nighttime temperatures at 15 °C. Relative humidity was maintained between 50% and 65%, with a photoperiod of 14 h of light and 10 h of darkness. Upon reaching the flowering stage in a controlled greenhouse with temperatures of 25 °C during the day and 15 °C at night, the strawberries were irrigated every 2 days and supplied twice a week with 0.5 L half-strength Hoagland’s solution for 16 weeks.

Estimation of lethal-dose thresholds

The dose mortality response of strawberry plants was analyzed using a linear regression. For each irradiation dose, mortality was calculated from the total number of irradiated plants across the three biological replicates. The cumulative proportion of mortality was modeled as a function of gamma-irradiation dose, and LD25, LD50, and LD75 values were estimated as the doses corresponding to 25%, 50%, and 75% predicted mortality, respectively. 95% confidence intervals were calculated for the estimated lethal doses.

Measurements of plant growth characteristics

Two months after planting, under optimal conditions, the plant height, leaf width, leaf length, fresh weight, and dry weight were measured. The leaf count per plant in each pot was determined, and the average leaf count was calculated. The total leaf area was assessed using ImageJ software and an automatic electronic leaf area meter (model LI 3000, U.S.A.). In addition, root morphometric traits, such as the number of roots, highest root, and root volume, were measured. The crown diameter of each plant under different treatments was recorded in centimeters using a meter scale, and the root number was counted. After separating the roots from the base of the runner, the fresh weight was assessed using a digital balance. Samples of shoots, leaves, and roots were dried in an oven for 72 h at 65 °C and then weighed using a Mettler Viper BC analytical scale to determine the dry weight of the shoot, root and shoot biomass. The root volume was calculated using a graduated cylinder. All dimensional measurements were recorded using the corresponding measuring instruments with a resolution of 0.01 cm or 0.1 mm, as appropriate, and mass measurements were recorded to the nearest 0.01 g. The same units and number of decimal places were used consistently in the Results, tables, and figures.

Measurements of fruit characteristics

The number of fruits per plant was determined by counting the fruits on each plant in every pot. Fruit length and diameter were assessed using a Digital Caliper (DC-515) in millimeters (mm), and the mature fruit weight was determined using a Mettler Viper BC analytical scale.

Statistical analysis

The experiment was conducted using a completely randomized design with three replicates. The statistical significance of the differences between mean values was determined using one-way analysis of variance (ANOVA), followed by Duncan’s multiple range test for mean separation. All statistical procedures were performed using SAS software (version 9.4; SAS Institute Inc., Cary, NC, USA). Significant differences were evaluated at a 1% level of significance.

Results

Effect of gamma irradiation on plant survival and dose response relationship

Gamma irradiation progressively reduced the survival of strawberry plantlets as the irradiation dose increased (Table 1; Fig. 1). All plantlets survived at 0 and 10 Gy, indicating that low-dose irradiation did not adversely affect plant viability. However, survival declined to 80.0% at 20 Gy and further decreased to 63.3% at 30 Gy. A pronounced reduction was observed at 40 Gy, where survival reached 48.3%, corresponding to a reduction of more than 50% relative to the control. At higher irradiation levels, survival continued to decrease, reaching 41.7%, 36.7%, 38.3%, 26.7%, 16.7%, and 15.0% at 50, 60, 70, 80, 90, and 100 Gy, respectively (Table 1).

Table 1.

Effect of different gamma irradiation doses on the survival of strawberry plantlets. Data are presented as the mean of three biological replicates

Gamma dose (Gy)	Number of plantlets	Survival (%)	Survival over control (%)	Reduction over control (%)
0	60	100.00	100.00	–
10	60	100.00	100.00	0.00
20	60	80.00	80.00	20.00
30	60	63.33	63.33	36.67
40	60	48.33	48.33	51.67
50	60	41.67	41.67	58.33
60	60	36.67	36.67	63.33
70	60	38.33	38.33	61.67
80	60	26.67	26.67	73.33
90	60	16.67	16.67	83.33
100	60	15.00	15.00	85.00

Fig. 1.

Linear dose response regression illustrating the relationship between gamma irradiation dose and mortality percentage of strawberry plantlets. The fitted regression line was used to estimate the LD₂₅, LD₅₀, and LD₇₅ values

The reduction in survival was accompanied by a gradual increase in mortality with increasing gamma-ray dose. Linear dose-response analysis revealed a strong relationship between irradiation dose and mortality percentage, with a coefficient of determination (R² = 0.94), indicating that approximately 94% of the variation in mortality was explained by irradiation dose (Fig. 1). Based on the regression analysis, the estimated lethal doses (LD) causing 25%, 50%, and 75% mortality were approximately 23.6 Gy, 51.7 Gy, and 79.8 Gy, respectively. These findings indicate that irradiation doses above approximately 60 Gy substantially reduced plant survival, whereas doses below 30 Gy caused only limited mortality while maintaining a relatively high proportion of surviving plantlets.

Effect of gamma rays on leaf characteristics

Table 2 indicates that the 30 Gy gamma ray dose had the highest leaf number (8.7), which did not differ significantly with the 40 Gy treatment. The leaf area improved when the gamma radiation dose was raised to 30 Gy, after which it began to decline. The 30 Gy treatment produced the most leaf area (8118 mm²), whereas the 100 Gy treatment caused the least leaf area (4775.7 mm²) (Table 2). The highest leaf length (142.03 mm) was recorded in the treatment with 20 Gy of gamma radiation, whereas the maximum leaf width (101.58 mm) was measured in the treatment with 20 Gy of gamma radiation. Table 2 shows that leaves exposed to 30 Gy of gamma radiation had the highest fresh weight (2.69 g) and dry weight (0.83 g); in contrast, plants exposed to 100 Gy of gamma radiation had the lowest fresh and dry leaf weights.

Table 2.

Mean comparison table of the effect of different gamma ray treatments on strawberry leaf characteristics

Treatment	Leaf number	Leaf area (mm2)	Leaf width (mm)	Leaf length (mm)
Control	6.31 ± 0.47 cd	6963.30 ± 515.54 cd	90.01 ± 6.43d	128.38 ± 7.71c
10	6.63 ± 0.47c	7203.10 ± 607.97bc	92.43 ± 6.38c	135.98 ± 7.45b
20	7.65 ± 1.25bc	7564.72 ± 99.55b	101.58 ± 1.79a	142.03 ± 5.89a
30	8.77 ± 0.47a	8118.03 ± 448.83a	95.62 ± 9.12b	131.58 ± 5.38b
40	8.00 ± 0.82ab	7081.30 ± 1064.13c	92.95 ± 2.03c	133.10 ± 1.96b
50	6.09 ± 0.01d	6804.01 ± 1209.68 cd	93.24 ± 4.78bc	126.53 ± 21.08c
60	5.61 ± 0.47e	5963.30 ± 768.58d	86.12 ± 5.05e	120.77 ± 2.83 cd
70	5.35 ± 0.47ef	5447.31 ± 231.31e	85.71 ± 14.82e	117.30 ± 1.60d
80	5.04 ± 0.82f	5115.70 ± 475.88f	82.90 ± 4.39ef	115.66 ± 6.90d
90	5.00 ± 0.02f	4985.01 ± 264.76 fg	75.33 ± 5.81f	115.20 ± 10.38d
100	4.69 ± 0.47 h	4775.77 ± 477.69 g	71.73 ± 6.18 g	113.93 ± 2.42e

Values are presented as mean ± standard error (SE), n = 3. Different lowercase letters indicate significant differences among treatments according to Duncan’s multiple range test (P ≤ 0.01)

Effect of gamma rays on root characteristics

The 30 Gy gamma treatment produced the longest roots (20.66 cm), whereas the 100 Gy gamma dose produced the shortest roots (11.63 cm) (Table 3). The greatest fresh weight of the roots was attained at 30 Gy (11.37 g); these values did not differ significantly from the 20 and 40 Gy gamma doses (Table 3). According to Table 3, the root dry weight was highest (2.98 g) at 20 Gy and lowest (2.17 g) at 100 Gy. Moreover, there was no significant difference in the root dry weight detected at 80 and 90-Gy gamma doses. The treatment with 40 Gy gamma had the maximum root volume (17.83 cm³), which did not differ significantly from the treatment performed with 30 Gy Gamma. The treatment with 100 Gy gamma (10.33 cm³) also had the lowest root volume, and there was no noticeable difference between it and the treatment with 90 Gy. A similar dose-dependent pattern was observed for root number. Root number increased at low doses, reaching 13.33 roots plant⁻¹ at 20 Gy compared with 11.00 roots plant⁻¹ in the control, and subsequently declined at higher doses, reaching 9.66 and 9.33 roots plant⁻¹ at 90 and 100 Gy, respectively (Table 3).

Table 3.

Mean comparison table of the effect of different gamma ray treatments on strawberry root characteristics

Treatment	Root length (cm)	Root fresh weight (g)	Root dry weight (g)	Root volume (cm3)	Root number (roots plant⁻¹)
Control	17.50 ± 0.86c	7.93 ± 0.54cde	2.69 ± 0.06b	15.00 ± 0.10d	11.00 ± 1.69c
10	17.83 ± 1.66bc	8.58 ± 0.73bcd	2.75 ± 0.16b	15.56 ± 0.47c	12.30 ± 0.47b
20	18.13 ± 1.07b	9.53 ± 1.10abc	2.98 ± 0.15a	16.33 ± 0.47b	13.33 ± 0.47a
30	20.66 ± 0.52a	11.37 ± 0.51a	2.74 ± 0.04b	17.00 ± 0.82ab	12.00 ± 1.88b
40	17.96 ± 0.34bc	10.66 ± 0.32ab	2.74 ± 0.17b	17.83 ± 0.23a	11.40 ± 0.81c
50	15.50 ± 1.28d	8.03 ± 1.32cde	2.71 ± 0.01b	14.66 ± 0.47d	11.20 ± 0.94 cd
60	14.53 ± 1.40e	7.57 ± 1.06cde	2.58 ± 0.05bc	13.17 ± 0.62de	10.65 ± 0.81d
70	13.76 ± 0.96f	7.01 ± 1.07ed	2.45 ± 0.09c	13.01 ± 0.81de	10.30 ± 0.94d
80	13.03 ± 0.41f	6.55 ± 1.68ed	2.31 ± 0.09 cd	12.00 ± 0.81e	10.30 ± 0.47d
90	12.46 ± 0.38 g	9.29 ± 0.11ed	2.19 ± 0.06d	11.00 ± 0.81ef	9.66 ± 0.47f
100	11.63 ± 0.84 h	6.00 ± 0.62e	2.17 ± 0.10d	10.33 ± 0.47f	9.33 ± 0.23f

Values are presented as mean ± standard error (SE), n = 3. Different lowercase letters indicate significant differences among treatments according to Duncan’s multiple range test (P ≤ 0.01)

Effect of gamma rays on fruit characteristics

Figure 2 shows that at 90 Gy and above, the Camarosa cultivar failed to produce fruit. Additionally, the results indicate that the fruit number decreases gradually as the gamma irradiation doses increase, with the exception of low doses of 10 (3.6), 20 (4), and 30 (4.3) Gy (Fig. 2). According to the findings of this investigation, the maximum fruit weights (9.14 and 9.19 g) were recorded in the 20 and 30-Gy gamma radiation. In other words, after being exposed to gamma radiation for 30 Gy, the fruit’s weight grew and subsequently declined. Although the fruit diameter reached its maximum in the 10 Gy gamma radiation (21.83 mm), there was no statistically significant difference between the 20 and 10 Gy. Additionally, fruit length decreased above 40 Gy, with the maximum length recorded following 20 Gy gamma radiation treatment (25.45 mm).

Fig. 2.

Impact of various gamma irradiation doses on the fruit traits of strawberry plants. The panels represent: (a) fruit weight, (b) fruit diameter, (c) fruit number, and (d) fruit length. Data are expressed as means ± SE (n = 3). Different lowercase letters indicate significant differences among treatments according to Duncan’s multiple range test at P ≤ 0.01

Effect of gamma radiation on plant biomass

The results of this research showed that a similar trend was observed with the fresh and dry weight of leaves for the aerial parts (Fig. 3). The highest fresh weight (68.7 g) and dry weight (35.59 g) of the aerial part were observed in the treatment with 30-Gy gamma radiation. In the investigations, it was found that the biomass fresh weight (80.83 g) reached its highest value in the treatment of 20 Gy of gamma radiation, whereas the treatment of 30 Gy of gamma radiation had the highest biomass dry weight (45.17 g).

Fig. 3.

Impact of various gamma irradiation doses on the growth parameters of strawberry plants. The panels represent: (a) aerial fresh weight, (b) aerial dry weight, (c) total biomass fresh weight, and (d) total biomass dry weight. Data are expressed as means ± standard error (n = 3). Different lowercase letters indicate significant differences among treatments according to Duncan’s multiple range test at P ≤ 0.01

Effect of gamma radiation on reproductive characteristics

The maximum crown diameter was observed at 10 Gy (3.30 cm), which did not differ significantly from the 20 Gy (3.29 cm) and 30 Gy (3.23 cm) treatments. The lowest crown diameter was recorded at 100 Gy (1.20 cm) (Fig. 4). The height of the plant decreased gradually from the treatment of 30 Gy gamma rays to the treatment of 100 Gy, with the treatment of 100 Gy producing the shortest height of the plants (9.86 cm). The treatment with 30 Gy (16.66) gamma radiation produced the highest number of flowers per plant, while the high dose of gamma radiation significantly reduced the number of flowers in the strawberry plant (Fig. 4).

Fig. 4.

Impact of various gamma irradiation doses on the growth and reproductive parameters of strawberry plants. The panels represent: (a) crown diameter; (b) plant height; and (c) flower number of strawberry. The means with the same letters in each column are not statistically significant (P ≤ 0.01). Data are expressed as means ± SE (n = 3). Different lowercase letters indicate significant differences among treatments according to Duncan’s multiple range test at P ≤ 0.01

Multivariate analyses

Cluster analysis

The main objective of the cluster analysis was to offer a thorough depiction of the morphophysiological traits that result from plants exposed to different levels of gamma radiation. The cluster analysis approach revealed three distinct groupings (Fig. 5). The first group comprised the control (untreated plants) and gamma irradiation at 20, 30, and 40 Gy. Application of 30 Gy was the most effective for increasing the growth and productivity of the tested subjects since it provided the maximum value for growth morpho physiological traits and fruit yield. This result is in agreement with previous studies that reported that low to moderate doses of gamma radiation stimulate growth due to favorable genetic changes or hormesis, a phenomenon wherein a sub lethal dose of a particular stressor increases, altogether, the growth and adaptational capability of a plant.

Fig. 5.

Cluster analysis of the studied traits in different gamma treatments. Abbreviations: Fruit number = Fn; Fruit weight = FW; Fruit length = FL; Fruit diameter = Fdia; Root number = root nu; leaf length = L lenghth; Aerial dry weight = ae dw; Leaf fresh weight = leaf fw; Leaf area = LA; Root dry weight = root dw; Fresh weight biomass = fw bio; Aerial fresh weight = aerial fw; Root length=root L; Dry weight biomass = dw bio; Plant height = height; Root volume = root volume; Flower number = flower n; Collar diameter = collar diameter; Leaf number = leaf n; Root fresh weight = root fw; leaf width = leaf width and leaf dry weight = leaf dw

The second group exhibited a more complex structure, with the two subgroups indicating varied responses to gamma irradiation at 10 and 50 Gy (Fig. 5). Individuals in the third group received high doses of gamma radiation, including 60, 70, 80, 90, and 100 Gy. Significant morphological and physiological damage was observed in this group, especially at higher doses (80, 90, and 100 Gy), when the negative effects of radiation were most noticeable. Due to the significant cellular and genetic damage that inhibits normal development processes, these plants clustered together, reflecting the severe stress and possible mortality imposed by such high doses. This result emphasizes the need for dose optimization in gamma irradiation research, as very high doses might have unfavorable effects that surpass any possible advantages of induced mutagenesis.

PCA

Combining PCA and cluster analysis enables a comprehensive understanding of the plant response spectrum to various gamma ray doses. As illustrated in Fig. 6, the two main components (PC1 and PC2) accounted for 88.72% of the total variance. A clear differentiation between high and low gamma radiation rates was observed in the variables related to PC1. Three distinct groups emerged from the cluster analysis (Fig. 6), corroborated by the PCA results. The first group comprised 20, 30, and 40 Gy gamma treatments. The second group was associated with doses ranging from 0 (control), 10, and 50 Gy. Conversely, the high-dose radiation treatment clustered into two separate groups: the first group included 60, 70, and 80 Gy, while the other group comprised 90 and 100 Gy, exhibiting the most significant adverse impacts on the morphophysiological state of strawberry plants.

Fig. 6.

Biplot of Principal Component Analysis (PCA) showing the associations between studied traits in response to gamma irradiation treatments. GD = gamma dose; LN = leaf number; FN = fruit number; He = plant height; CD = collar diameter; LA = leaf area; LW = leaf width; LL = leaf length; RL = root length; RFW = root fresh weight; RDW = root dry weight; RV = root volume; RN = root number; FWB = fresh weight biomass; DWB = dry weight biomass; AFW = aerial fresh weight; ADW = aerial dry weight; LFW = leaf fresh weight; LDW = leaf dry weight; FrN = flower number; FrL = fruit length; FrD = fruit diameter; and FrW = fruit weight

Correlation analysis

Correlation analysis revealed strong negative associations between gamma dose and several morphological, biomass, root, and fruit traits (Fig. 7). The strongest negative correlations were observed for root dry weight (r = -0.91), aerial dry weight (r = -0.89), leaf area (r = -0.88), aerial fresh weight (r = -0.88), fruit number (r = -0.88), leaf length (r = -0.87), and leaf width (r = -0.83). Gamma dose was also negatively correlated with biomass fresh weight (r = -0.82), fruit diameter (r = -0.80), and fruit weight (r = -0.80). Moderate negative correlations were observed for crown diameter, root fresh weight, leaf dry weight, leaf number, flower number, and fruit length (r = –0.67 to –0.79).

Fig. 7.

Pearson’s correlation matrix showing the relationships among morphological, biomass, root, leaf, flower, and fruit-related traits of plants subjected to different gamma irradiation doses. Correlation coefficients are represented by colored circles, where circle size and color intensity are proportional to the strength of the correlation. Blue and red colors indicate positive and negative correlations, respectively. Asterisks denote significant correlations (*P < 0.05, P < 0.01). Abbreviations: GD = gamma dose; LN = leaf number; FN = fruit number; He = plant height; CD = collar diameter; LA = leaf area; LW = leaf width; LL = leaf length; RL = root length; RFW = root fresh weight; RDW = root dry weight; RV = root volume; RN = root number; FWB = fresh weight biomass; DWB = dry weight biomass; AFW = aerial fresh weight; ADW = aerial dry weight; LFW = leaf fresh weight; LDW = leaf dry weight; FrN = flower number; FrL = fruit length; FrD = fruit diameter; and FrW = fruit weight

Discussion

Gamma irradiation is well known to enhance the growth characteristics of numerous economically significant plants, especially at lower doses [23]. Gamma irradiation reduced the survival of strawberry plantlets in a dose-dependent manner, with a marked decline observed at doses of 40 Gy and above. In contrast, complete survival at 10 Gy indicates that this dose remained below the radiosensitivity threshold of the cultivar and did not cause irreversible damage. The survival response observed in the present study was broadly comparable to previous reports in strawberry, although the estimated lethal threshold differed among cultivars and experimental systems. In the present study, LD50 was estimated at 51.7 Gy, whereas Rodge et al. [24] reported an LD50 of approximately 40 Gy for strawberry cv. Winter Dawn. This difference may reflect cultivar-specific radiosensitivity as well as differences in propagule type, irradiation conditions, and experimental design. The relatively higher LD50 observed for Camarosa suggests greater tolerance to gamma irradiation under the conditions used in the present study.

The estimated lethal doses obtained in this study provide a useful reference for future mutation breeding of strawberry. In mutation breeding programs, irradiation doses close to the LD₅₀ are generally considered suitable because they provide an appropriate balance between mutation induction and plant survival [25]. Therefore, the survival response observed in the present study provides a biological basis for interpreting the effects of low-dose gamma irradiation on subsequent growth and flowering characteristics.

The response of strawberry plants to gamma irradiation observed in the present study is broadly consistent with previous reports. R Gupta, P Bakshi and RA Shah [26] found that low gamma-ray doses of 10 and 30 Gy maintained or enhanced vegetative performance of strawberry axillary buds, particularly leaf number and petiole length, whereas higher doses of 50 and 60 Gy resulted in reduced growth, smaller leaf area and fruit size, and abnormal fruit development. Similarly, Rodge et al. [24] reported dose-dependent responses in strawberry cv. ‘Winter Dawn’, with 20–30 Gy producing favorable growth and flowering responses, while higher doses progressively reduced plant performance. These findings are consistent with the present results and support the occurrence of a dose-dependent response in strawberry, in which relatively low irradiation doses can be tolerated or may stimulate selected developmental traits, whereas increasing doses increasingly impose detrimental effects. In addition, recent work on strawberry callus cultures showed that low-dose gamma irradiation (15–40 Gy) did not significantly reduce biomass accumulation, although dose-dependent responses were observed for biochemical characteristics [27]. Thus, the responses observed in the present study are in agreement with previous strawberry studies and further demonstrate that the biological effects of gamma irradiation depend strongly on irradiation dose and the biological material exposed.

Increased growth, as indicated by Capsicum annuum L. shoot length, diameter, and leaf area, was observed at radiation doses of 24 Gy compared with the control group [28]. IM Farid, A El-Nabarawy, MH Abbas, A Morsy, M Afifi, H Abbas and M Hekal [29] recorded significantly improved growth performance of Vicia faba at doses ≤ 100 Gy; however, higher doses had negative effects on the plant. SG Wi, BY Chung, J-S Kim, J-H Kim, M-H Baek, J-W Lee and YS Kim [30] found that giving a pumpkin plant a high dose of gamma radiation (1 kGy) can disrupt the balance of plant growth regulators, leading to curled and yellowed leaves. Vanhoudt et al. [31] demonstrated that different doses of gamma rays caused changes in root and leaf weight, but growth was not inhibited. These changes were attributed to biological factors rather than radiation-induced effects.

Fresh weight and dry weight in plant are related to physiologically parameters. Fresh weight reflects both biomass accumulation and tissue water content, whereas dry weight represents the actual amount of organic matter produced through photosynthesis process and assimilate partitioning. Consequently, treatments that affect water retention and dry matter accumulation differently may result in distinct responses of fresh and dry biomass. Although biomass fresh weight was slightly higher at 20 Gy than at 30 Gy, biomass dry weight in strawberry reached its maximum at 30 Gy. This indicates that plants exposed to 30 Gy accumulated a greater proportion of structural and metabolic dry matter relative to tissue water content. Fresh weight is strongly influenced by plant water status, whereas dry weight of plant reflects the actual accumulation of biomass. Therefore, the higher dry weight in strawberry observed at 30 Gy suggests improved assimilate accumulation and biomass production efficiency rather than merely increased water retention. Vanhoudt et al. [31] reported that low doses of gamma radiation improved photosynthetic performance by increasing PSII efficiency and maximal electron transport rate in Arabidopsis thaliana, suggesting stimulation of carbon assimilation processes.

Gamma radiation affects roots differently depending on the dose rate and duration of exposure; longer exposure results in more severe development suppression than shorter exposure [32]. According to previous studies, gamma irradiation can affect the length, diameter, size, and weight of roots [33]. Furthermore, high dose of gamma irradiation can decrease the fresh and dry weight, as well as the length, of the roots and stems [34]. Gamma radiation also causes chromosomal aberrations in the root cells, which impact cell proliferation and division [35]. According to M Melki and A Marouani [36] findings, wheat roots developed more readily at low doses of gamma irradiation than at higher doses, which inhibited root development. Bajaj et al. [37], gamma irradiation disrupts the synthesis of proteins and RNA, which in turn prevents plants from growing in vitro. Furthermore, AA Ghasemi-Soloklui, M Kordrostami and R Karimi [38] found that increasing the gamma dose had a negative effect on vine root growth, as evidenced by a decrease in root number, root volume, and root biomass of the ‘Yaghouti’ grape. In general, exposure to gamma rays changes the characteristics of roots, and the use of a gamma low dose can improve root plant development.

In another study, strawberry fruit length decreased at higher gamma radiation doses. Conversely, elongating strawberry fruit in low doses of gamma has also been documented [39, 40]. Plants receiving higher doses of gamma radiation exhibit smaller fruit and dwarfism because of decreased leaf area, an increase in gamma radiation dose, and a decrease in total photosynthesis. S Velu, L Mullainathan, D Arulbalachandran, D Dhanavel and R Poongkuzhali [41] reported that with the increase in gamma radiation intensity, the number of small fruits increases, and the malformation of plants also increases with the increase in radiation intensity. Moreover, plants with short phenotypes are the result of a mutation that affects the gibberellic acid (GA) signaling pathway or its biosynthesis [42].

According to the study findings, strawberry plants exposed to low doses of gamma radiation could have better growth characteristics. This may be due to the regulatory effects of low-dose gamma irradiation on genes involved in these traits and the enhanced activity of hormones and enzymes essential to growth pathways. Moreover, a low dose of gamma could accelerate the increase in cell division in meristematic tissues, which might improve plant development, according to research by Dhakshanamoorthy et al. [43]. In addition, low doses of gamma irradiation may improve the growth hormone interactions and raise the antioxidant potentials in the radiated cells, potentially leading to improved growth [30]. H-I Choi, SM Han, YD Jo, MJ Hong, SH Kim and J-B Kim [44] observed that growth anomalies in plants exposed to higher doses of gamma irradiation are commonly linked to the ionization of cell water and the consequent generation of reactive oxygen species and free radicals. Thus, these molecules can interact with other cellular molecules, potentially imposing negative structural and functional changes in them [45]. These findings are consistent with previous studies in other species, excessive doses of gamma rays were shown in this study to have an adverse impact on plant growth [41, 46]. An increase in radiation exposure because of DNA mutations that disrupt plant buds and stop cell differentiation by synthesizing DNA during the interphase. An increase in gamma radiation damages plant cells and eventually prevents plants from growing [47].

The stimulatory effect at 30 Gy is likely associated with a hormetic response to low-dose gamma irradiation. At this dose, irradiation may induce a moderate rise in ROS levels, which function as secondary messengers in stress signaling pathways and trigger the activation of antioxidant defense systems. This activation can enhance ROS scavenging capacity and protect cellular components from oxidative damage. Moreover, low-dose irradiation may influence phytohormonal homeostasis, including auxins, gibberellins, and abscisic acid, leading to improved growth regulation and stress adaptation. Therefore, the enhanced growth observed at 30 Gy may reflect a balance between stress signaling and defense activation that promotes physiological performance in strawberry plants [48]. On the other hand, cell cycle arrest at the Gap 2/Mitosis (G2/M) phase during somatic cell division and/or different damages throughout the entire genome have been linked to high-dose irradiation that caused growth inhibition.

A decrease in meristematic cell mitotic activity, auxin biosynthesis, changes in ascorbic acid levels, and disruptions in physiological and biochemical features appear to be among the causes of stem diameter reduction [49]. Low-dose gamma irradiation could have triggered the upregulation of these genes or other signaling pathways involved in flower development [50]. There are two possible explanations for this: first, during the early stages of flower development, mutations may have led to cell misplacement; second, meristems may follow the central organs during flower development [51]. This is because radiation breaks DNA in plant cells, which further damages plant growth, cell division, and development processes [8, 52].

Overall, the cluster analysis results demonstrate that strawberry plants may be effectively grouped based on their responses to different gamma radiation doses, providing valuable insights into dosage-dependent impacts. The findings demonstrate how important it is to optimize gamma radiation doses to obtain the desired agronomic characteristics without jeopardizing plant life. The cluster analysis method can also be used in breeding programs to select radiation-responsive plants [53, 54]. In this study, however, the method’s application can be used to determine the most effective ways to improve the growth and reproductive properties of strawberries at different gamma doses.

In general, the combination of cluster analysis with PCA allows deep insight into the dose-dependent effects of gamma radiation on strawberry plants. A number of response groups were observed, which again underlines the importance of optimizing the gamma radiation doses to achieve the necessary results in mutagenesis and plant development experiments [38]. This approach will provide insight into not only the basic processes underlying the radiation-induced changes but also information that may be useful for increasing crop productivity by controlled exposure to gamma radiation [55, 56].

The high negative correlation between gamma dose and root dry weight indicates a considerable reduction in the biomass of the root with increased intensity of radiation, which could adversely affect plant water and nutrient uptake and have cascading effects on overall plant growth and biomass yield [57, 58]. Moreover, decreased leaf length, leaf width, and fruit diameter fit the hypothesis that a higher dose of gamma radiation could influence vegetative and reproductive growth by the possible induction of cellular damage and interference with growth-regulating pathways [59, 60].

Strong negative correlations with aerial biomass, leaf surface area, and fruit number also suggested that higher levels of gamma radiation disrupted photosynthetic efficiency and reproductive functionality, resulting in reduced plant vigor and productivity. The observed shortening of the length and width of the leaves and fruits also supported the contention that higher doses of gamma radiation negatively impact vegetative and reproductive growth, presumably due to the direct damage to cellular structures involved in growth and development, along with interference with the mechanism controlling growth [61–63]. Even the positive associations among different morpho-physiological traits, for instance, leaf, root, and fruit, suggest that these are interdependent; in other words, good conditions given to one part of the plant have positive effects on the others.

Overall, these findings highlight the importance of carefully selecting appropriate levels of gamma radiation for programs related to plant mutation breeding or for investigating the hormesis effect, which confers optimum growth and reproductive responses in plants. Moreover, low doses of radiation can be used to achieve beneficial effects and enhance certain attributes, whereas high doses of gamma radiation can be extremely detrimental, causing a reduction in the general plant efficacy and productivity. This study reinforces the need for a balanced approach when using gamma radiation to modify plant genetic traits, particularly for optimizing crop improvement strategies.

Conclusion

Gamma irradiation induced a clear dose-dependent response in strawberry, with low-to-moderate doses improving several vegetative, biomass, root, and reproductive traits, while higher doses progressively reduced plant survival and performance. The LD25, LD50, and LD75 were estimated at 23.6, 51.7, and 79.8 Gy, respectively. Among the tested treatments, 30 Gy produced the most favorable overall response, particularly for leaf development, root growth, biomass accumulation, flower production, and fruit traits. In contrast, doses ≥ 60 Gy markedly reduced survival and most growth and reproductive parameters, with severe effects at 80–100 Gy. PCA and cluster analyses further distinguished the stimulatory low-to-moderate dose range from the detrimental high-dose treatments. Therefore, a moderate gamma-ray dose (30 Gy) produced the most favorable growth, root development, and flowering responses in strawberry, suggesting a hormetic effect. In contrast, doses above 50 Gy caused greater growth inhibition and survival reduction and may therefore be considered candidate doses for subsequent mutation-breeding studies, pending confirmation of heritable genetic variation.

Authors’ contributions

Ali Akbar Ghasemi-Soloklui: Conceptualization, Methodology, Funding acquisition, Investigation, Project administration, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing. Mojtaba Kordrostami: Data curation, Formal analysis, Investigation, Methodology, Software, Supervision, Validation, Writing – review & editing. Saeed Moori: Conceptualization, Investigation, Methodology, Validation, Writing – review & editing. Masoud Shahmoradi: Data curation, Methodology, Investigation, Validation, Writing – review & editing. All authors read and approved the final manuscript.

Funding

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Data availability

The data used to support the findings of this study are included within the article.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.