Effect of gamma irradiation on growth parameters of mutated mandarin orange (Citrus Reticulata Blanco)

Introduction

The genus Citrus is one of the most economically important fruit crops in the world, widely cultivated for its nutritious juice, edible pulp, and commercially valuable by-products. It belongs to the sub-tribe Citrineae, sub-family Aurantioideae and family Rutaceae and comprises 162 species according to Tanaka's classification. Citrus crops are widely grown in tropical and subtropical regions of the world and occupy a prominent position in global fruit production. Citrus is cultivated in about 137 countries, and global citrus production reached 166.30 million tonnes during 2023. China, Brazil, and India are the leading citrus-producing countries, contributing 48.77, 19.73, and 14.76 million tonnes, respectively. Among citrus fruits, sweet orange accounts for the largest share of global production (45.95%), followed by mandarins, tangerines, and clementines (26.57%), lemons and limes (12.95%), pummelo and grapefruit (5.87%), and other citrus fruits (8.67%). (Kamatyanatt et al., 2021) [8] . India ranks as the third largest producer of citrus fruits globally, following China and Brazil. Other major citrus producing countries include Spain, United States, Israel, Morocco, South Africa, Japan, Turkey and Cuba. Among the various citrus fruits cultivated in India, mandarins lead in both area and production followed by sweet oranges and limes. In the 2023-24 season, mandarin cultivation covered approximately 4.74 lakh hectares and yielding around 60.75 lakh metric tonnes (Anonymous, 2024). The leading mandarin growing states in India are Maharashtra, Andhra Pradesh, Punjab, Karnataka, Orrisa, Bihar, Assam, Tamil Nadu and Gujarat. Maharashtra is one of the leading citrus producing states of India, where mandarin and sweet orange constitute a major share of the citrus area and production. The total production of mandarin in Maharashtra 1342.78 thousand MT from an area of 143.72 thousand hectares with a productivity of 9.34 MT ha - 1 (Anonymous, 2024). Within Maharashtra, the Vidarbha region, particularly the districts of Nagpur and Amravati forms the principal mandarin belt, where Nagpur mandarin is predominantly cultivated. Inducing mutations by gamma-rays has been effectively used in several species of citrus. Irradiation of budwood with gamma rays can produce higher frequencies of mutation, leading to the creation of new variants compared to the parent variety. Gamma irradiation based mutagenesis of budwood has been the most commonly used method by citrus breeders worldwide to obtain seedless clones from commercial seeded varieties of orange, mandarin, grapefruit and lemon. An alternative method to obtain seedless citrus fruit is through breeding of triploid trees. Physical mutagens induce gross lesions, such as chromosomal abbreviation or rearrangements. It is noteworthy that the frequency and types of mutations are direct results of the dosage and rate of exposure or administration of the mutagen rather than its type (Mba et al., 2012) [12] In India, mutagenesis studies have been taken up for acid lime, sweet orange and mandarins and the resulting plants are in the initial stages of valuation. Considering the commercial importance of Nagpur mandarin and the growing need for genetically improved planting material, the present investigation was undertaken to evaluate the effect of different doses of gamma irradiation on growth parameters of mutated Nagpur mandarin and Nagpur seedless under field conditions. The study aimed to study the effect of gamma rays on plant height, leaf length, leaf width, number of leaves and branching behaviour.

Materials and Methods

Experimental Site

The present investigation was conducted during the years 2022-23, 2023-24 and 2024-25 at Futala Farm, Horticulture Section, College of Agriculture, Nagpur, under Dr. Panjabrao Deshmukh Krishi Vidyapeeth (PDKV), Akola, Maharashtra, India. The experimental site is situated in the subtropical climatic region of central India and falls within the Vidarbha agro-climatic zone, which is characterized by hot summers, mild winters and monsoon-dominated rainfall patterns. The region experiences an average annual rainfall of approximately 1000-1200 mm, most of which is received during the southwest monsoon season. The soil of the experimental field was well-drained and suitable for citrus cultivation.

Plant material

Two mandarin varieties, namely Nagpur mandarin and Nagpur seedless (Citrus reticulata Blanco.) belonging to the family Rutaceae, were used as experimental material for the study. Healthy and uniform bud stick of both varieties were selected and utilized for mutation induction treatments. After gamma irradiation treatment, the bud sticks of Nagpur mandarin and Nagpur seedless were budded on rough lemon rootstock planted in polythene bags of size 8-12 inch. Once the budded plants attained sufficient growth (approximately 30 to 45 cm in height), they were hardened and subsequently transplanted to the open field to carry out systematic data recording on key morphological parameters, including plant height, leaf length, leaf width, number of leaves plant -1 and number of branches plant -1 .

Gamma irradiation treatment

The budstick of both mandarin genotypes were subjected to gamma irradiation using a Cobalt-60 (Co-60) gamma radiation source prior to planting. Five different doses of gamma rays, viz., 10, 20, 30, 40 and 50 Gy, were employed to induce mutagenic variability. Untreated cuttings of both genotypes served as controls. The experiment was laid out in a Randomized Block Design (RBD) comprising eleven treatments with three replications. All irradiated and control plants were planted under uniform field conditions and maintained using standard cultural practices recommended for mandarin cultivation.

Treatment details

Observations recorded

To evaluate the effect of gamma irradiation on vegetative growth behaviour, observations on plant height, leaf length, leaf width, number of leaves plant -1 and number of branches plant -1 were recorded periodically over the experimental duration.

Plant height was measured from the ground level to the apical growing point using a measuring scale and expressed in centimetres. Observations were recorded at 4 month intervals from 4 months after planting (MAP) up to 32 MAP.

Length of leaf was measured with measuring scale at an interval of 4 month after planting upto 32 month after planting. The length of leaf was measured from the base of the petiole to the tip of the leaf and was expressed in centimeter (cm).

Leaf width was measured at the center of leaf with measuring scale at an interval of 4 month after planting upto 32 month after planting. The width of the leaf was expressed in centimeter (cm)

Number of leaves plant -1

Average number of leaves per plant of bud grafts was recorded at an interval of 2 month after planting.

Number of branches plant -1

The number of branches plant -1 was recorded as cumulative counts of primary, secondary and tertiary branches. Primary branches were counted at 2 MAP, primary and secondary branches at 4 MAP and cumulative primary, secondary and tertiary branches at 6 MAP.

Statistical analysis

The experimental data generated during the course of investigation were subjected to statistical analysis using analysis of variance (ANOVA) appropriate for Randomized Block Design as described by Panse and Sukhatme (1985) [13] . The significance of treatment effects was using the F-test at 5 per cent probability level. Whenever treatment differences were found significant, the Critical Difference (CD) at 5% level of significance was calculated for comparison of treatment means. Standard Error of Mean [S.E.(m)±] values were also computed for all recorded observations. The observed responses were interpreted on the basis of dose-dependent effects of gamma irradiation on vegetative growth and branching behaviour of the mandarin genotypes under field conditions.

Result and discussion

Effect of gamma irradiation on growth parameters of mutated mandarin orange (citrus reticulata blanco.)

The effect of different doses of gamma irradiation on vegetative growth parameters of mutated Nagpur mandarin and Nagpur seedless was evaluated under field conditions over a period extending from 2 to 32 months after planting (MAP). The observations recorded on plant height, leaf length, leaf width, number of leaves plant -1 and number of branches plant -1 revealed significant variations among treatments at different growth stages, indicating a pronounced influence of gamma irradiation on vegetative development and canopy architecture of mandarin orange.

Effect of Gamma Irradiation on Plant Height

The data pertaining to plant height are presented in [15] in rough lemon, Kumar et al., (2023) [10] in Kinnow mandarin, Singh et al., (2018) [17] in Guava, Manjusha et al., (2024) [11] in Acid lime, Ghasemi-Soloklui et al., (2025) [6] in Fig, Srikanth et al., (2026) [18] in Litchi. Brar and Bal (2003) [4] in Guava, Kaur and Rattanpal (2008) in rough lemon, Sharafi et al., (2013) [16] in almond.

Effect of gamma radiation doses on leaf length of mandarin mutant.

The data regarding leaf length presented in [19] in grape, Rattanpal et al., (2019) [14] in Mandarin, Ghasemi-Soloklui et al., (2025) [6] in fig who noticed the significant reduction in leaf length after radiation as compared to the control.

Effect of gamma radiation doses on leaf width of mandarin mutant

The analysis of data on leaf width is presented in Table 3 [19] in grape, Rattanpal et al., (2019) [14] in Mandarin, Ghasemi-Soloklu et al., (2025) [6] in fig who reported that a gradual decrease in leaf width was observed with higher irradiation doses. [1] in banana and Jyoti et al., (2026) [7] in mandarin who reported that gamma irradiation had no significant impact on leaf number, however no clear mutation trend was observed in irradiated treatments. Among Nagpur mandarin mutants, at 2 months after planting, the maximum number of primary branches (6.17) was observed in NM + 40 Gy (T5) followed by NM + 30 GY (T4) (5.12) while the minimum number of primary branches was observed in NM (Control) (T1) (3.17). At 4 months after planting, maximum number of primary and secondary branches was observed in NM + 40 Gy (T5) (18.00) which was at par with NM + 30 Gy (T4) (17.20), while minimum number of primary, secondary branches was recorded by NM (control) (10.56). At 6 MAP, maximum number of primary, secondary and tertiary branches was observed in NM + 40 Gy (T5) (22.50) followed by NM + 30 Gy (21.03), while minimum number of primary, secondary and tertiary branches was recorded by NM (control) (16.79). Among Nagpur seedless mutants, at 2 months after planting, the maximum number of primary branches (6.33) was observed in NS + 40 Gy (T10) which was at par with NS +50 Gy (T11) (5.90), while the minimum number of primary branches was observed in NS (Control) (T6) (3.19). At 4 months after planting, maximum number of primary and secondary branches was observed in NS + 40 Gy (T10) (18.67) followed by NS + 30 Gy (T9) (17.17), while minimum number of primary and secondary branches was recorded by NS (control) (T6) (13.90). At 6 MAP, maximum number of primary, secondary and tertiary branches was observed in NS + 40 Gy (T10) (22.67) followed by NM + 30 Gy (T9) (21.07), while minimum number of primary, secondary and tertiary branches was recorded by NS (control) (18.73). Radiation treatments probably induced some changes at the gene level that ultimately reflected in substances that trigger biochemical processes controlling different aspects of growth. These substances, identified as auxins, gibberellins, ethylene and abscisic acid called phytohormones, initiates biochemical reactions and induce changes in chemical patterns that lead to various modifications and variations in plant characters, viz., height, branching and stem thickness, as mentioned in Saini and Gill (2009) [15] . These results are close findings with Brar and Bal (2003) [4] , Singh et al., (2018) [17] in guava, Saini and Gill (2009) [15] in rough lemon and Jyoti et al., (2026) [7] in mandarin who reported that number of branches per plant increased with increase in gamma irradiation doses.

Conclusion

The present investigation demonstrated that gamma irradiation significantly influenced the vegetative growth behaviour of Nagpur mandarin and Nagpur seedless in a dose-dependent manner under field conditions. Increasing doses of gamma rays progressively reduced plant height, leaf length, leaf width whereas branching behaviour increased up to moderate irradiation levels before declining at the highest dose. However, number of leaves showed in irregular trend. Gamma irradiation does not disrupt the fundamental rhythm of leaf initiation. Lower doses of 10 Gy and 20 Gy maintained vegetative growth comparatively close to untreated controls, indicating their biological suitability for mutation breeding programmes, while higher doses, particularly 40 Gy and 50 Gy, caused severe suppression of growth parameters. Overall, the findings indicate that gamma irradiation can serve as an effective tool for inducing useful morphological variability in citrus, and irradiation doses between 10 and 20 Gy may be considered optimal for generating agronomically viable mutant lines for future citrus improvement programmes.

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